diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/OverrideResolutionPass.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/OverrideResolutionPass.java
index 80a9563d9f..f2f7dcc4aa 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/OverrideResolutionPass.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/ast/OverrideResolutionPass.java
@@ -23,7 +23,7 @@ import net.sourceforge.pmd.lang.java.types.TypeOps;
  * @author Clément Fournier
  * @since 7.0.0
  */
-class OverrideResolutionPass {
+final class OverrideResolutionPass {
 
     private OverrideResolutionPass() {
 
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/codestyle/UnnecessaryImportRule.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/codestyle/UnnecessaryImportRule.java
index 79cf14ca2d..c34697dc07 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/codestyle/UnnecessaryImportRule.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/codestyle/UnnecessaryImportRule.java
@@ -315,12 +315,8 @@ public class UnnecessaryImportRule extends AbstractJavaRule {
                             // maybe we're importing a subclass of the container.
                             TypeSystem ts = symbolOwner.getTypeSystem();
                             JClassSymbol importedContainer = ts.getClassSymbol(it.node.getImportedName());
-                            if (importedContainer != null) {
-                                return TypeTestUtil.isA(ts.rawType(symbolOwner), ts.rawType(importedContainer));
-                            } else {
-                                // insufficient classpath, err towards FNs
-                                return true;
-                            }
+                            return importedContainer == null // insufficient classpath, err towards FNs
+                                    || TypeTestUtil.isA(ts.rawType(symbolOwner), ts.rawType(importedContainer));
                         }
                     });
                 }
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/CouplingBetweenObjectsRule.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/CouplingBetweenObjectsRule.java
index dfea612724..3ce63e495c 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/CouplingBetweenObjectsRule.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/CouplingBetweenObjectsRule.java
@@ -132,7 +132,7 @@ public class CouplingBetweenObjectsRule extends AbstractJavaRule {
         }
         JTypeDeclSymbol symbol = t.getSymbol();
         return symbol == null
-            || symbol.getPackageName().equals(JAccessibleElementSymbol.PRIMITIVE_PACKAGE)
+            || JAccessibleElementSymbol.PRIMITIVE_PACKAGE.equals(symbol.getPackageName())
             || t.isPrimitive()
             || t.isBoxedPrimitive();
     }
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/LawOfDemeterRule.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/LawOfDemeterRule.java
index 574c9c7967..fb9c6777bf 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/LawOfDemeterRule.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/LawOfDemeterRule.java
@@ -90,7 +90,7 @@ public class LawOfDemeterRule extends AbstractJavaRule {
      * Collects the information of one identified method call. The method call
      * might be a violation of the Law of Demeter or not.
      */
-    private static class MethodCall {
+    private static final class MethodCall {
         private static final String METHOD_CALL_CHAIN = "result from previous method call";
         private static final String SIMPLE_ASSIGNMENT_OPERATOR = "=";
         private static final String SCOPE_METHOD_CHAINING = "method-chaining";
@@ -193,10 +193,8 @@ public class LawOfDemeterRule extends AbstractJavaRule {
 
         private static boolean isNotLiteral(ASTPrimaryExpression expression) {
             ASTPrimaryPrefix prefix = expression.getFirstDescendantOfType(ASTPrimaryPrefix.class);
-            if (prefix != null) {
-                return !prefix.hasDescendantOfType(ASTLiteral.class);
-            }
-            return true;
+            return prefix == null
+                    || !prefix.hasDescendantOfType(ASTLiteral.class);
         }
 
         private boolean isNotBuilder() {
@@ -275,7 +273,7 @@ public class LawOfDemeterRule extends AbstractJavaRule {
             violationReason = null;
 
             if (baseNameInWhitelist) {
-                return;
+                violation = false;
             } else if (SCOPE_LOCAL.equals(baseScope)) {
                 Assignment lastAssignment = determineLastAssignment();
                 if (lastAssignment != null && !lastAssignment.allocation && !lastAssignment.iterator
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/documentation/CommentSizeRule.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/documentation/CommentSizeRule.java
index 8c708b017c..6edff2a963 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/documentation/CommentSizeRule.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/documentation/CommentSizeRule.java
@@ -48,12 +48,7 @@ public class CommentSizeRule extends AbstractJavaRulechainRule {
     }
 
     private static boolean hasRealText(String line) {
-
-        if (StringUtils.isBlank(line)) {
-            return false;
-        }
-
-        return !IGNORED_LINES.contains(line.trim());
+        return !StringUtils.isBlank(line) && !IGNORED_LINES.contains(line.trim());
     }
 
     private boolean hasTooManyLines(Comment comment) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/errorprone/CloneMethodMustImplementCloneableRule.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/errorprone/CloneMethodMustImplementCloneableRule.java
index 8f9328669a..e58eea9a7e 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/errorprone/CloneMethodMustImplementCloneableRule.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/errorprone/CloneMethodMustImplementCloneableRule.java
@@ -47,10 +47,8 @@ public class CloneMethodMustImplementCloneableRule extends AbstractJavaRulechain
     }
 
     private static boolean justThrowsCloneNotSupported(ASTBlock body) {
-        if (body.size() != 1) {
-            return false;
-        }
-        return body.getChild(0)
+        return body.size() == 1
+                && body.getChild(0)
                    .asStream()
                    .filterIs(ASTThrowStatement.class)
                    .map(ASTThrowStatement::getExpr)
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/AnnotationSuppressionUtil.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/AnnotationSuppressionUtil.java
index 87955a509d..1396be92b9 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/AnnotationSuppressionUtil.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/AnnotationSuppressionUtil.java
@@ -81,11 +81,7 @@ final class AnnotationSuppressionUtil {
      */
     private static boolean suppresses(final Node node, Rule rule) {
         Annotatable suppressor = getSuppressor(node);
-        if (suppressor == null) {
-            return false;
-        }
-
-        return hasSuppressWarningsAnnotationFor(suppressor, rule);
+        return suppressor != null && hasSuppressWarningsAnnotationFor(suppressor, rule);
     }
 
     @Nullable
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/DataflowPass.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/DataflowPass.java
index 4bb5c89f50..0321bf67f5 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/DataflowPass.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/DataflowPass.java
@@ -296,7 +296,7 @@ public final class DataflowPass {
         }
     }
 
-    private static class ReachingDefsVisitor extends JavaVisitorBase<SpanInfo, SpanInfo> {
+    private static final class ReachingDefsVisitor extends JavaVisitorBase<SpanInfo, SpanInfo> {
 
 
         static final ReachingDefsVisitor ONLY_LOCALS = new ReachingDefsVisitor(null, false);
@@ -862,11 +862,9 @@ public final class DataflowPass {
         }
 
         private boolean isRelevantField(ASTExpression lhs) {
-            if (!(lhs instanceof ASTNamedReferenceExpr)) {
-                return false;
-            }
-            return trackThisInstance() && JavaRuleUtil.isThisFieldAccess(lhs)
-                || trackStaticFields() && isStaticFieldOfThisClass(((ASTNamedReferenceExpr) lhs).getReferencedSym());
+            return (lhs instanceof ASTNamedReferenceExpr)
+                && (trackThisInstance() && JavaRuleUtil.isThisFieldAccess(lhs)
+                        || trackStaticFields() && isStaticFieldOfThisClass(((ASTNamedReferenceExpr) lhs).getReferencedSym()));
         }
 
         private boolean isStaticFieldOfThisClass(JVariableSymbol var) {
@@ -1022,7 +1020,7 @@ public final class DataflowPass {
      * The shared state for all {@link SpanInfo} instances in the same
      * toplevel class.
      */
-    private static class GlobalAlgoState {
+    private static final class GlobalAlgoState {
 
         final Set<AssignmentEntry> allAssignments;
         final Set<AssignmentEntry> usedAssignments;
@@ -1082,7 +1080,7 @@ public final class DataflowPass {
     /**
      * Information about a span of code.
      */
-    private static class SpanInfo {
+    private static final class SpanInfo {
 
         // spans are arranged in a tree, to look for enclosing finallies
         // when abrupt completion occurs. Blocks that have non-local
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/JavaRuleUtil.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/JavaRuleUtil.java
index 1c48bea09a..05c5d1de77 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/JavaRuleUtil.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/JavaRuleUtil.java
@@ -174,10 +174,9 @@ public final class JavaRuleUtil {
      * This also considers long literals.
      */
     public static boolean isLiteralInt(JavaNode e, int value) {
-        if (e instanceof ASTNumericLiteral) {
-            return ((ASTNumericLiteral) e).isIntegral() && ((ASTNumericLiteral) e).getValueAsInt() == value;
-        }
-        return false;
+        return e instanceof ASTNumericLiteral
+                && ((ASTNumericLiteral) e).isIntegral()
+                && ((ASTNumericLiteral) e).getValueAsInt() == value;
     }
 
     /** This is type-aware, so will not pick up on numeric addition. */
@@ -237,10 +236,8 @@ public final class JavaRuleUtil {
      * is a main method.
      */
     public static boolean isMainMethod(JavaNode node) {
-        if (node instanceof ASTMethodDeclaration) {
-            return ((ASTMethodDeclaration) node).isMainMethod();
-        }
-        return false;
+        return node instanceof ASTMethodDeclaration
+                && ((ASTMethodDeclaration) node).isMainMethod();
     }
 
     /**
@@ -508,10 +505,8 @@ public final class JavaRuleUtil {
     }
 
     public static boolean isAnonymousClassCreation(@Nullable ASTExpression expression) {
-        if (expression instanceof ASTConstructorCall) {
-            return ((ASTConstructorCall) expression).isAnonymousClass();
-        }
-        return false;
+        return expression instanceof ASTConstructorCall
+                && ((ASTConstructorCall) expression).isAnonymousClass();
     }
 
     /**
@@ -689,14 +684,12 @@ public final class JavaRuleUtil {
             return false;
         }
         JVariableSymbol sym = ((ASTNamedReferenceExpr) e).getReferencedSym();
-        if (sym instanceof JFieldSymbol) {
-            return !((JFieldSymbol) sym).isStatic()
+        return sym instanceof JFieldSymbol
+                && !((JFieldSymbol) sym).isStatic()
                 // not inherited
                 && ((JFieldSymbol) sym).getEnclosingClass().equals(e.getEnclosingType().getSymbol())
                 // correct syntactic form
                 && (e instanceof ASTVariableAccess || isSyntacticThisFieldAccess(e));
-        }
-        return false;
     }
 
     /**
@@ -744,10 +737,8 @@ public final class JavaRuleUtil {
      * that references the symbol.
      */
     public static boolean isReferenceToVar(@Nullable ASTExpression expression, @NonNull JVariableSymbol symbol) {
-        if (expression instanceof ASTNamedReferenceExpr) {
-            return symbol.equals(((ASTNamedReferenceExpr) expression).getReferencedSym());
-        }
-        return false;
+        return expression instanceof ASTNamedReferenceExpr
+                && symbol.equals(((ASTNamedReferenceExpr) expression).getReferencedSym());
     }
 
     public static boolean isUnqualifiedThis(ASTExpression e) {
@@ -763,10 +754,8 @@ public final class JavaRuleUtil {
      * that references any of the symbol in the set.
      */
     public static boolean isReferenceToVar(@Nullable ASTExpression expression, @NonNull Set<? extends JVariableSymbol> symbols) {
-        if (expression instanceof ASTNamedReferenceExpr) {
-            return symbols.contains(((ASTNamedReferenceExpr) expression).getReferencedSym());
-        }
-        return false;
+        return expression instanceof ASTNamedReferenceExpr
+                && symbols.contains(((ASTNamedReferenceExpr) expression).getReferencedSym());
     }
 
     /**
@@ -817,10 +806,8 @@ public final class JavaRuleUtil {
      * Returns true if the expression is a reference to a local variable.
      */
     public static boolean isReferenceToLocal(ASTExpression expr) {
-        if (expr instanceof ASTVariableAccess) {
-            return ((ASTVariableAccess) expr).getReferencedSym() instanceof AstLocalVarSym;
-        }
-        return false;
+        return expr instanceof ASTVariableAccess
+                && ((ASTVariableAccess) expr).getReferencedSym() instanceof AstLocalVarSym;
     }
 
     /**
@@ -920,14 +907,12 @@ public final class JavaRuleUtil {
                 && (isNonLocalLhs(lhs) || isReferenceToVar(lhs, localVarsToTrack));
         }
 
-        if (e.ancestors(ASTThrowStatement.class).nonEmpty()) {
-            // then this side effect can never be observed in containing code,
-            // because control flow jumps out of the method
-            return false;
-        }
-
-        return e instanceof ASTMethodCall && !isPure((ASTMethodCall) e)
-            || e instanceof ASTConstructorCall;
+        // when there are throw statements,
+        // then this side effect can never be observed in containing code,
+        // because control flow jumps out of the method
+        return e.ancestors(ASTThrowStatement.class).isEmpty()
+                && (e instanceof ASTMethodCall && !isPure((ASTMethodCall) e)
+                        || e instanceof ASTConstructorCall);
     }
 
     private static boolean isNonLocalLhs(ASTExpression lhs) {
@@ -996,10 +981,7 @@ public final class JavaRuleUtil {
     }
 
     public static boolean isArrayInitializer(ASTExpression expr) {
-        if (expr instanceof ASTArrayAllocation) {
-            return ((ASTArrayAllocation) expr).getArrayInitializer() != null;
-        }
-        return false;
+        return expr instanceof ASTArrayAllocation && ((ASTArrayAllocation) expr).getArrayInitializer() != null;
     }
 
     public static boolean isCloneMethod(ASTMethodDeclaration node) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/StablePathMatcher.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/StablePathMatcher.java
index c6df092758..65977f2dba 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/StablePathMatcher.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/StablePathMatcher.java
@@ -77,10 +77,8 @@ public final class StablePathMatcher {
             return Objects.equals(((ASTVariableAccess) e).getReferencedSym(), owner);
         } else if (e instanceof ASTFieldAccess) {
             ASTFieldAccess fieldAccess = (ASTFieldAccess) e;
-            if (!JavaRuleUtil.isUnqualifiedThis(fieldAccess.getQualifier())) {
-                return false;
-            }
-            return Objects.equals(fieldAccess.getReferencedSym(), owner);
+            return JavaRuleUtil.isUnqualifiedThis(fieldAccess.getQualifier())
+                    && Objects.equals(fieldAccess.getReferencedSym(), owner);
         }
         return false;
     }
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/TestFrameworksUtil.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/TestFrameworksUtil.java
index f6c9da0eb1..91470fef89 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/TestFrameworksUtil.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/internal/TestFrameworksUtil.java
@@ -136,11 +136,9 @@ public final class TestFrameworksUtil {
     public static boolean isCallOnAssertionContainer(ASTMethodCall call) {
         JTypeMirror declaring = call.getMethodType().getDeclaringType();
         JTypeDeclSymbol sym = declaring.getSymbol();
-        if (sym instanceof JClassSymbol) {
-            return ASSERT_CONTAINERS.contains(((JClassSymbol) sym).getBinaryName())
-                || TypeTestUtil.isA("junit.framework.Assert", declaring);
-        }
-        return false;
+        return sym instanceof JClassSymbol
+                && (ASSERT_CONTAINERS.contains(((JClassSymbol) sym).getBinaryName())
+                        || TypeTestUtil.isA("junit.framework.Assert", declaring));
     }
 
     public static boolean isProbableAssertCall(ASTMethodCall call) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/ConsecutiveLiteralAppendsRule.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/ConsecutiveLiteralAppendsRule.java
index 1238a746d1..948cae7590 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/ConsecutiveLiteralAppendsRule.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/ConsecutiveLiteralAppendsRule.java
@@ -276,7 +276,7 @@ public class ConsecutiveLiteralAppendsRule extends AbstractJavaRulechainRule {
             || TypeTestUtil.isA(StringBuilder.class, node);
     }
 
-    private static class ConsecutiveCounter {
+    private static final class ConsecutiveCounter {
         private int threshold;
         private int counter;
         private Node reportNode;
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/FlexibleUnresolvedClassImpl.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/FlexibleUnresolvedClassImpl.java
index 33c4933582..f3914b9723 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/FlexibleUnresolvedClassImpl.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/FlexibleUnresolvedClassImpl.java
@@ -49,7 +49,7 @@ final class FlexibleUnresolvedClassImpl extends UnresolvedClassImpl {
     void setTypeParameterCount(int newArity) {
         if (arity == UNKNOWN_ARITY) {
             this.arity = newArity;
-            ArrayList<JTypeVar> newParams = new ArrayList<>(newArity);
+            List<JTypeVar> newParams = new ArrayList<>(newArity);
             for (int i = 0; i < newArity; i++) {
                 newParams.add(new FakeTypeParam("T" + i, getTypeSystem(), this).getTypeMirror());
             }
@@ -83,7 +83,7 @@ final class FlexibleUnresolvedClassImpl extends UnresolvedClassImpl {
         return tparams;
     }
 
-    private static class FakeTypeParam implements JTypeParameterSymbol {
+    private static final class FakeTypeParam implements JTypeParameterSymbol {
 
         private final String name;
         private final JTypeParameterOwnerSymbol owner;
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/SymbolToStrings.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/SymbolToStrings.java
index 169a6e4e71..8e24d277fe 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/SymbolToStrings.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/SymbolToStrings.java
@@ -32,7 +32,7 @@ public class SymbolToStrings {
         return symbol.acceptVisitor(visitor, new StringBuilder()).toString();
     }
 
-    private static class ToStringVisitor implements SymbolVisitor<StringBuilder, StringBuilder> {
+    private static final class ToStringVisitor implements SymbolVisitor<StringBuilder, StringBuilder> {
 
         private final String impl;
 
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/asm/AsmSymbolResolver.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/asm/AsmSymbolResolver.java
index 81d537a020..a0b5d4d72e 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/asm/AsmSymbolResolver.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/asm/AsmSymbolResolver.java
@@ -7,6 +7,7 @@ package net.sourceforge.pmd.lang.java.symbols.internal.asm;
 
 import java.net.URL;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -30,7 +31,7 @@ public class AsmSymbolResolver implements SymbolResolver {
     private final Classpath classLoader;
     private final SignatureParser typeLoader;
 
-    private final ConcurrentHashMap<String, SoftClassReference> knownStubs = new ConcurrentHashMap<>();
+    private final ConcurrentMap<String, SoftClassReference> knownStubs = new ConcurrentHashMap<>();
 
     /**
      * Sentinel for when we fail finding a URL. This allows using a single map,
@@ -124,6 +125,7 @@ public class AsmSymbolResolver implements SymbolResolver {
         knownStubs.put(internalName, softRef);
     }
 
+    @SuppressWarnings("PMD.CompareObjectsWithEquals") // SoftClassReference
     @NonNull JClassSymbol resolveFromInternalNameCannotFail(@NonNull String internalName, int observedArity) {
         return knownStubs.compute(internalName, (iname, prev) -> {
             if (prev != failed && prev != null) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/asm/TypeSigParser.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/asm/TypeSigParser.java
index 91f400ac4b..d19a977b11 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/asm/TypeSigParser.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/internal/asm/TypeSigParser.java
@@ -8,6 +8,7 @@ import static java.util.Collections.emptyList;
 
 import java.util.ArrayDeque;
 import java.util.ArrayList;
+import java.util.Deque;
 import java.util.List;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
@@ -276,8 +277,8 @@ final class TypeSigParser {
     abstract static class TypeScanner extends SignatureScanner {
 
         // those stacks usually are 0..1
-        private final ArrayDeque<JTypeMirror> typeStack = new ArrayDeque<>(0);
-        private final ArrayDeque<List<JTypeMirror>> listStack = new ArrayDeque<>(0);
+        private final Deque<JTypeMirror> typeStack = new ArrayDeque<>(0);
+        private final Deque<List<JTypeMirror>> listStack = new ArrayDeque<>(0);
 
         private final TypeSystem ts;
         private final LexicalScope lexicalScope;
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/coreimpl/CoreResolvers.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/coreimpl/CoreResolvers.java
index 52fc80d219..8a3deb6478 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/coreimpl/CoreResolvers.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/coreimpl/CoreResolvers.java
@@ -55,7 +55,7 @@ public final class CoreResolvers {
         return new SingularMapResolver<>(singular);
     }
 
-    private static class SingularMapResolver<S> implements SingleNameResolver<S> {
+    private static final class SingularMapResolver<S> implements SingleNameResolver<S> {
 
         private final Map<String, S> map;
 
@@ -127,7 +127,7 @@ public final class CoreResolvers {
         return EmptyResolver.INSTANCE;
     }
 
-    private static class EmptyResolver<S> implements SingleNameResolver<S> {
+    private static final class EmptyResolver<S> implements SingleNameResolver<S> {
 
         private static final EmptyResolver INSTANCE = new EmptyResolver<>();
 
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/coreimpl/MostlySingularMultimap.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/coreimpl/MostlySingularMultimap.java
index d347e0f841..8d7f0aa582 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/coreimpl/MostlySingularMultimap.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/coreimpl/MostlySingularMultimap.java
@@ -23,7 +23,7 @@ import net.sourceforge.pmd.internal.util.AssertionUtil;
  * An unmodifiable multimap type, efficient if the single-value case is the
  * most common.
  */
-class MostlySingularMultimap<K, V> {
+final class MostlySingularMultimap<K, V> {
 
     @SuppressWarnings("rawtypes")
     private static final MostlySingularMultimap EMPTY = new MostlySingularMultimap<>(Collections.emptyMap());
@@ -111,7 +111,7 @@ class MostlySingularMultimap<K, V> {
     /**
      * Builder for a multimap. Can only be used once.
      */
-    public static class Builder<K, V> {
+    public static final class Builder<K, V> {
 
         private final MapMaker<K> mapMaker;
         private @Nullable Map<K, Object> map;
@@ -225,7 +225,7 @@ class MostlySingularMultimap<K, V> {
                 if (noDuplicate && vs.equals(v)) {
                     return vs;
                 }
-                VList<V> vs2 = new VList<>(2);
+                List<V> vs2 = new VList<>(2);
                 isSingular = false;
                 vs2.add((V) vs);
                 vs2.add(v);
@@ -241,7 +241,7 @@ class MostlySingularMultimap<K, V> {
         public @Nullable Map<K, V> buildAsSingular() {
             consume();
             if (!isSingular) {
-                return null;
+                return Collections.emptyMap();
             }
             return (Map<K, V>) map;
         }
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/ReferenceCtx.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/ReferenceCtx.java
index 71fad661d2..063f1613c8 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/ReferenceCtx.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/ReferenceCtx.java
@@ -6,10 +6,10 @@ package net.sourceforge.pmd.lang.java.symbols.table.internal;
 
 import static net.sourceforge.pmd.lang.java.symbols.table.internal.JavaSemanticErrors.AMBIGUOUS_NAME_REFERENCE;
 import static net.sourceforge.pmd.lang.java.symbols.table.internal.JavaSemanticErrors.CANNOT_RESOLVE_MEMBER;
-import static net.sourceforge.pmd.lang.java.types.JVariableSig.FieldSig;
 
 import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -25,6 +25,7 @@ import net.sourceforge.pmd.lang.java.symbols.JTypeParameterSymbol;
 import net.sourceforge.pmd.lang.java.symbols.table.JSymbolTable;
 import net.sourceforge.pmd.lang.java.types.JClassType;
 import net.sourceforge.pmd.lang.java.types.JTypeMirror;
+import net.sourceforge.pmd.lang.java.types.JVariableSig.FieldSig;
 
 /**
  * Context of a usage reference ("in which class does the name occur?"),
@@ -81,7 +82,7 @@ public final class ReferenceCtx {
             return null;
         } else if (found.size() > 1) {
             // FIXME when type is reachable through several paths, there may be duplicates!
-            HashSet<? extends T> distinct = new HashSet<>(found);
+            Set<? extends T> distinct = new HashSet<>(found);
             if (distinct.size() == 1) {
                 return distinct.iterator().next();
             }
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/SuperTypesEnumerator.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/SuperTypesEnumerator.java
index b60fb4650d..3890162836 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/SuperTypesEnumerator.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/SuperTypesEnumerator.java
@@ -59,6 +59,7 @@ public enum SuperTypesEnumerator {
             @Nullable JClassType sup = t.getSuperClass();
             List<JClassType> superItfs = t.getSuperInterfaces();
 
+            @SuppressWarnings("PMD.LooseCoupling") // the set should keep insertion order
             LinkedHashSet<JClassType> set;
             if (sup != null) {
                 set = new LinkedHashSet<>(superItfs.size() + 1);
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/SymbolTableResolver.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/SymbolTableResolver.java
index 51a62119f2..ffada9506f 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/SymbolTableResolver.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symbols/table/internal/SymbolTableResolver.java
@@ -84,7 +84,7 @@ public final class SymbolTableResolver {
         } while (!todo.isEmpty());
     }
 
-    private static class DeferredNode {
+    private static final class DeferredNode {
 
         final JavaNode node;
         // this is data used to resume the traversal
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/DeclarationFinderFunction.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/DeclarationFinderFunction.java
index 9dd5336959..7239c5b450 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/DeclarationFinderFunction.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/DeclarationFinderFunction.java
@@ -37,11 +37,8 @@ public class DeclarationFinderFunction implements Predicate<NameDeclaration> {
     }
 
     private boolean isDeclaredBefore(NameDeclaration nameDeclaration) {
-        if (nameDeclaration.getNode() != null && occurrence.getLocation() != null) {
-            return nameDeclaration.getNode().getBeginLine() <= occurrence.getLocation().getBeginLine();
-        }
-
-        return true;
+        return nameDeclaration.getNode() == null || occurrence.getLocation() == null
+                || nameDeclaration.getNode().getBeginLine() <= occurrence.getLocation().getBeginLine();
     }
 
     private boolean isSameName(NameDeclaration nameDeclaration) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/JavaNameOccurrence.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/JavaNameOccurrence.java
index 168da97e0c..e4688e7748 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/JavaNameOccurrence.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/JavaNameOccurrence.java
@@ -96,23 +96,11 @@ public class JavaNameOccurrence implements NameOccurrence {
                             + " (location line " + location.getBeginLine() + " col " + location.getBeginColumn() + ")");
         }
 
-        if (isStandAlonePostfix(primaryExpression)) {
-            return true;
-        }
-
-        if (primaryExpression.getNumChildren() <= 1) {
-            return false;
-        }
-
-        if (!(primaryExpression.getChild(1) instanceof ASTAssignmentOperator)) {
-            return false;
-        }
-
-        if (isPartOfQualifiedName() /* or is an array type */) {
-            return false;
-        }
-
-        return !isCompoundAssignment(primaryExpression);
+        return isStandAlonePostfix(primaryExpression)
+                || primaryExpression.getNumChildren() > 1
+                    && primaryExpression.getChild(1) instanceof ASTAssignmentOperator
+                    && !isPartOfQualifiedName() /* and is not an array type */
+                    && !isCompoundAssignment(primaryExpression);
     }
 
     private boolean isCompoundAssignment(Node primaryExpression) {
@@ -134,11 +122,8 @@ public class JavaNameOccurrence implements NameOccurrence {
 
         ASTPrimaryPrefix pf = (ASTPrimaryPrefix) ((ASTPrimaryExpression) primaryExpression.getChild(0))
             .getChild(0);
-        if (pf.usesThisModifier()) {
-            return true;
-        }
 
-        return thirdChildHasDottedName(primaryExpression);
+        return pf.usesThisModifier() || thirdChildHasDottedName(primaryExpression);
     }
 
     private boolean thirdChildHasDottedName(Node primaryExpression) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/TypeSet.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/TypeSet.java
index 20ae57d9c5..f128299a41 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/TypeSet.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/TypeSet.java
@@ -12,6 +12,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 import net.sourceforge.pmd.annotation.InternalApi;
 import net.sourceforge.pmd.lang.java.typeresolution.PMDASMClassLoader;
@@ -291,7 +292,7 @@ public class TypeSet {
          * cache to have ~90% hit ratio unless abusing star imports (import on
          * demand)
          */
-        private static final ConcurrentHashMap<String, Class<?>> CLASS_CACHE = new ConcurrentHashMap<>();
+        private static final ConcurrentMap<String, Class<?>> CLASS_CACHE = new ConcurrentHashMap<>();
 
         /**
          * Creates a {@link ImplicitImportResolver}
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/typeresolution/internal/NullableClassLoader.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/typeresolution/internal/NullableClassLoader.java
index b7ba7d8b89..51a28bfd3f 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/typeresolution/internal/NullableClassLoader.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/typeresolution/internal/NullableClassLoader.java
@@ -21,7 +21,7 @@ public interface NullableClassLoader {
     Class<?> loadClassOrNull(String binaryName);
 
 
-    class ClassLoaderWrapper implements NullableClassLoader {
+    final class ClassLoaderWrapper implements NullableClassLoader {
 
         private final ClassLoader classLoader;
 
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/InvocationMatcher.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/InvocationMatcher.java
index 0c52fe4b15..09224b77d1 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/InvocationMatcher.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/InvocationMatcher.java
@@ -80,10 +80,7 @@ public final class InvocationMatcher {
      * See {@link #matchesCall(InvocationNode)}.
      */
     public boolean matchesCall(@Nullable JavaNode node) {
-        if (node instanceof InvocationNode) {
-            return matchesCall((InvocationNode) node);
-        }
-        return false;
+        return node instanceof InvocationNode && matchesCall((InvocationNode) node);
     }
 
     /**
@@ -101,10 +98,8 @@ public final class InvocationMatcher {
             return false;
         }
         OverloadSelectionResult info = node.getOverloadSelectionInfo();
-        if (info.isFailed() || !matchQualifier(node)) {
-            return false;
-        }
-        return argsMatchOverload(info.getMethodType());
+        return !info.isFailed() && matchQualifier(node)
+                && argsMatchOverload(info.getMethodType());
     }
 
     private boolean matchQualifier(InvocationNode node) {
@@ -289,11 +284,9 @@ public final class InvocationMatcher {
         }
 
         boolean matches(JTypeMirror type, boolean exact) {
-            if (name == null) {
-                return true;
-            }
-            return exact ? TypeTestUtil.isExactlyAOrAnon(name, type) == OptionalBool.YES
-                         : TypeTestUtil.isA(name, type);
+            return name == null
+                   || (exact ? TypeTestUtil.isExactlyAOrAnon(name, type) == OptionalBool.YES
+                         : TypeTestUtil.isA(name, type));
         }
     }
 
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/JPrimitiveType.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/JPrimitiveType.java
index dcd2eaa06f..3b8eaf35e9 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/JPrimitiveType.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/JPrimitiveType.java
@@ -137,7 +137,7 @@ public final class JPrimitiveType implements JTypeMirror {
         FLOAT(float.class),
         DOUBLE(double.class);
 
-        static final EnumSet<PrimitiveTypeKind> FLOATING_POINT_TYPES = EnumSet.of(FLOAT, DOUBLE);
+        static final Set<PrimitiveTypeKind> FLOATING_POINT_TYPES = EnumSet.of(FLOAT, DOUBLE);
 
         final String name = name().toLowerCase(Locale.ROOT);
         private final Class<?> jvm;
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/JTypeMirror.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/JTypeMirror.java
index 5c1a67c6b0..551a170bd8 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/JTypeMirror.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/JTypeMirror.java
@@ -216,11 +216,9 @@ public interface JTypeMirror extends JTypeVisitable {
             return true;
         } else if (this instanceof JArrayType) {
             return ((JArrayType) this).getElementType().isReifiable();
-        } else if (this instanceof JClassType) {
-            return TypeOps.allArgsAreUnboundedWildcards(((JClassType) this).getTypeArgs());
-        } else {
-            return false;
         }
+
+        return this instanceof JClassType && TypeOps.allArgsAreUnboundedWildcards(((JClassType) this).getTypeArgs());
     }
 
 
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/Lub.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/Lub.java
index 154db01020..64c4e3918a 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/Lub.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/Lub.java
@@ -69,6 +69,7 @@ final class Lub {
      *
      * @return null if G is not a generic type, otherwise Relevant(G)
      */
+    @SuppressWarnings("PMD.ReturnEmptyCollectionRatherThanNull") // null is explicit mentioned as a possible return value
     static @Nullable List<JClassType> relevant(JClassType g, Set<JTypeMirror> stunion) {
         if (!g.isRaw()) {
             return null;
@@ -87,7 +88,7 @@ final class Lub {
     }
 
     private static Set<JTypeMirror> erasedSuperTypes(Set<JTypeMirror> stui) {
-        LinkedHashSet<JTypeMirror> erased = new LinkedHashSet<>();
+        Set<JTypeMirror> erased = new LinkedHashSet<>();
         for (JTypeMirror it : stui) {
             JTypeMirror t = it instanceof JTypeVar ? it : it.getErasure();
             erased.add(t);
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeConversion.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeConversion.java
index 5987a02d87..ed12290517 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeConversion.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeConversion.java
@@ -236,10 +236,8 @@ public final class TypeConversion {
      * wildcards as type arguments. Capture variables don't count.
      */
     public static boolean isWilcardParameterized(JTypeMirror t) {
-        if (!(t instanceof JClassType)) {
-            return false;
-        }
-        return CollectionUtil.any(((JClassType) t).getTypeArgs(), it -> it instanceof JWildcardType);
+        return t instanceof JClassType
+                && CollectionUtil.any(((JClassType) t).getTypeArgs(), it -> it instanceof JWildcardType);
     }
 
 
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeOps.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeOps.java
index bfe65d8abf..f95dd23617 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeOps.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeOps.java
@@ -117,7 +117,7 @@ public final class TypeOps {
         return true;
     }
 
-    private static class SameTypeVisitor implements JTypeVisitor<Boolean, JTypeMirror> {
+    private static final class SameTypeVisitor implements JTypeVisitor<Boolean, JTypeMirror> {
 
         static final SameTypeVisitor INFERENCE = new SameTypeVisitor(true);
         static final SameTypeVisitor PURE = new SameTypeVisitor(false);
@@ -222,10 +222,8 @@ public final class TypeOps {
 
         @Override
         public Boolean visitArray(JArrayType t, JTypeMirror s) {
-            if (s instanceof JArrayType) {
-                return isSameType(t.getComponentType(), ((JArrayType) s).getComponentType(), inInference);
-            }
-            return false;
+            return s instanceof JArrayType
+                    && isSameType(t.getComponentType(), ((JArrayType) s).getComponentType(), inInference);
         }
     }
 
@@ -1168,15 +1166,8 @@ public final class TypeOps {
         }
 
         JMethodSig m1Prime = adaptForTypeParameters(m1, m2);
-        if (m1Prime != null && isConvertible(m1Prime.getReturnType(), r2) != Convertibility.NEVER) {
-            return true;
-        }
-
-        if (!haveSameSignature(m1, m2)) {
-            return isSameType(r1, r2.getErasure());
-        }
-
-        return false;
+        return m1Prime != null && isConvertible(m1Prime.getReturnType(), r2) != Convertibility.NEVER
+                || !haveSameSignature(m1, m2) && isSameType(r1, r2.getErasure());
     }
 
     /**
@@ -1291,15 +1282,10 @@ public final class TypeOps {
      * Thrown exceptions are not part of the signature of a method.
      */
     private static boolean haveSameSignature(JMethodSig m1, JMethodSig m2) {
-        if (!m1.getName().equals(m2.getName()) || m1.getArity() != m2.getArity()) {
-            return false;
-        }
-
-        if (!haveSameTypeParams(m1, m2)) {
-            return false;
-        }
-
-        return areSameTypes(m1.getFormalParameters(),
+        return m1.getName().equals(m2.getName())
+                && m1.getArity() == m2.getArity()
+                && haveSameTypeParams(m1, m2)
+                && areSameTypes(m1.getFormalParameters(),
                             m2.getFormalParameters(),
                             Substitution.mapping(m2.getTypeParameters(), m1.getTypeParameters()));
     }
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypePrettyPrint.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypePrettyPrint.java
index e3bdbd9358..93bbe497fc 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypePrettyPrint.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypePrettyPrint.java
@@ -119,7 +119,7 @@ public final class TypePrettyPrint {
         }
     }
 
-    private static class PrettyPrintVisitor implements JTypeVisitor<Void, TypePrettyPrinter> {
+    private static final class PrettyPrintVisitor implements JTypeVisitor<Void, TypePrettyPrinter> {
 
         static final PrettyPrintVisitor INSTANCE = new PrettyPrintVisitor();
 
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeSystem.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeSystem.java
index 51a8a1f7ad..800b378730 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeSystem.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeSystem.java
@@ -102,7 +102,7 @@ public final class TypeSystem {
      * The set of all primitive types. See {@link #getPrimitive(PrimitiveTypeKind)}.
      */
     public final Set<JPrimitiveType> allPrimitives;
-    private final EnumMap<PrimitiveTypeKind, JPrimitiveType> primitivesByKind;
+    private final Map<PrimitiveTypeKind, JPrimitiveType> primitivesByKind;
 
     /**
      * A constant to represent the normal absence of a type. The
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeTestUtil.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeTestUtil.java
index f3c81422cb..d7547c4353 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeTestUtil.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/TypeTestUtil.java
@@ -60,12 +60,8 @@ public final class TypeTestUtil {
      */
     public static boolean isA(final @NonNull Class<?> clazz, final @Nullable TypeNode node) {
         AssertionUtil.requireParamNotNull("class", clazz);
-        if (node == null) {
-            return false;
-        }
-
-        return hasNoSubtypes(clazz) ? isExactlyA(clazz, node)
-                                    : isA(clazz, node.getTypeMirror());
+        return node != null && (hasNoSubtypes(clazz) ? isExactlyA(clazz, node)
+                                    : isA(clazz, node.getTypeMirror()));
     }
 
     /**
@@ -127,11 +123,7 @@ public final class TypeTestUtil {
 
     public static boolean isA(@NonNull String canonicalName, @Nullable JTypeMirror thisType) {
         AssertionUtil.requireParamNotNull("canonicalName", (Object) canonicalName);
-        if (thisType == null) {
-            return false;
-        }
-
-        return isA(canonicalName, thisType, null);
+        return thisType != null && isA(canonicalName, thisType, null);
     }
 
     public static boolean isA(@NonNull JTypeMirror t1, @Nullable TypeNode t2) {
@@ -208,19 +200,12 @@ public final class TypeTestUtil {
      */
     public static boolean isExactlyA(final @NonNull Class<?> clazz, final @Nullable TypeNode node) {
         AssertionUtil.requireParamNotNull("class", clazz);
-        if (node == null) {
-            return false;
-        }
-
-        return isExactlyA(clazz, node.getTypeMirror().getSymbol());
+        return node != null && isExactlyA(clazz, node.getTypeMirror().getSymbol());
     }
 
     public static boolean isExactlyA(@NonNull Class<?> klass, @Nullable JTypeMirror type) {
         AssertionUtil.requireParamNotNull("class", klass);
-        if (type == null) {
-            return false;
-        }
-        return isExactlyA(klass, type.getSymbol());
+        return type != null && isExactlyA(klass, type.getSymbol());
     }
 
     public static boolean isExactlyA(@NonNull Class<?> klass, @Nullable JTypeDeclSymbol type) {
@@ -272,10 +257,7 @@ public final class TypeTestUtil {
      */
     public static boolean isExactlyA(@NonNull String canonicalName, final @Nullable TypeNode node) {
         AssertionUtil.assertValidJavaBinaryName(canonicalName);
-        if (node == null) {
-            return false;
-        }
-        return isExactlyAOrAnon(canonicalName, node.getTypeMirror()) == OptionalBool.YES;
+        return node != null && isExactlyAOrAnon(canonicalName, node.getTypeMirror()) == OptionalBool.YES;
     }
 
     static OptionalBool isExactlyAOrAnon(@NonNull String canonicalName, final @NonNull JTypeMirror node) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/ast/ExprContext.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/ast/ExprContext.java
index 4cd08c218b..8f59b577cd 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/ast/ExprContext.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/ast/ExprContext.java
@@ -58,14 +58,12 @@ public abstract class ExprContext {
         AssertionUtil.requireParamNotNull("type", type);
 
         JTypeMirror targetType = getTargetType();
-        if (targetType == null) {
-            return true;
-        }
 
-        // todo there's a gritty detail about compound assignment operators
-        //  with a primitive LHS, see https://github.com/pmd/pmd/issues/2023
-        return kind == CAST ? TypeConversion.isConvertibleInCastContext(type, targetType)
-                            : TypeConversion.isConvertibleUsingBoxing(type, targetType);
+        return targetType == null
+                // todo there's a gritty detail about compound assignment operators
+                //  with a primitive LHS, see https://github.com/pmd/pmd/issues/2023
+                || (kind == CAST ? TypeConversion.isConvertibleInCastContext(type, targetType)
+                            : TypeConversion.isConvertibleUsingBoxing(type, targetType));
     }
 
     /**
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/ExprOps.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/ExprOps.java
index f6f0b64d7b..4847007b1c 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/ExprOps.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/ExprOps.java
@@ -143,26 +143,21 @@ final class ExprOps {
             //  not provide explicit type arguments, an explicitly typed
             //  lambda expression for which the corresponding target type
             //  (as derived from the signature of m) is a type parameter of m.
-            if (m.isGeneric() && invoc.getExplicitTypeArguments().isEmpty()) {
-                return !formalType.isTypeVariable();
-            }
-
-            return true;
+            return !m.isGeneric()
+                    || !invoc.getExplicitTypeArguments().isEmpty()
+                    || !formalType.isTypeVariable();
         }
 
         if (arg instanceof MethodRefMirror) {
             // An inexact method reference expression(§ 15.13 .1).
-            if (getExactMethod((MethodRefMirror) arg) == null) {
-                return false;
-            }
-            //  If m is a generic method and the method invocation does
-            //  not provide explicit type arguments, an exact method
-            //  reference expression for which the corresponding target type
-            //  (as derived from the signature of m) is a type parameter of m.
-            if (m.isGeneric() && invoc.getExplicitTypeArguments().isEmpty()) {
-                return !formalType.isTypeVariable();
-            }
-            return true;
+            return getExactMethod((MethodRefMirror) arg) != null
+                    //  If m is a generic method and the method invocation does
+                    //  not provide explicit type arguments, an exact method
+                    //  reference expression for which the corresponding target type
+                    //  (as derived from the signature of m) is a type parameter of m.
+                    && (!m.isGeneric()
+                        || !invoc.getExplicitTypeArguments().isEmpty()
+                        || !formalType.isTypeVariable());
         }
 
         if (arg instanceof BranchingMirror) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Graph.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Graph.java
index a4ef6e223a..ceddc46062 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Graph.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Graph.java
@@ -7,15 +7,16 @@ package net.sourceforge.pmd.lang.java.types.internal.infer;
 import static java.lang.Math.min;
 import static net.sourceforge.pmd.util.CollectionUtil.union;
 
+import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Deque;
 import java.util.HashMap;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import java.util.Stack;
 
 import net.sourceforge.pmd.internal.GraphUtils;
 import net.sourceforge.pmd.internal.GraphUtils.DotColor;
@@ -164,14 +165,14 @@ class Graph<T> {
         );
     }
 
-    private static class TarjanState<T> {
+    private static final class TarjanState<T> {
 
         int index;
-        Stack<Vertex<T>> stack = new Stack<>();
+        Deque<Vertex<T>> stack = new ArrayDeque<>();
 
     }
 
-    static class Vertex<T> {
+    static final class Vertex<T> {
 
         private final Graph<T> owner;
         private final Set<T> data;
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Infer.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Infer.java
index fdf63b9049..d819709b3a 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Infer.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/Infer.java
@@ -333,7 +333,7 @@ public final class Infer {
         subst(t.getReturnType(), var -> {
             assert !(var instanceof InferenceVar)
                 : "Expected a ground type " + t;
-            assert !(var instanceof JTypeVar) || !(t.getTypeParameters().contains(var))
+            assert !(var instanceof JTypeVar) || !t.getTypeParameters().contains(var)
                 : "Some type parameters have not been instantiated";
             return var;
         });
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceContext.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceContext.java
index aa805cacad..4cb1890ab8 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceContext.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceContext.java
@@ -80,6 +80,7 @@ final class InferenceContext {
      *                            into ivars
      * @param logger              Logger for events related to ivar bounds
      */
+    @SuppressWarnings("PMD.AssignmentToNonFinalStatic") // ctxId
     InferenceContext(TypeSystem ts, SupertypeCheckCache supertypeCheckCache, List<JTypeVar> tvars, TypeInferenceLogger logger) {
         this.ts = ts;
         this.supertypeCheckCache = supertypeCheckCache;
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceVar.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceVar.java
index 3c0bd5bfb3..be1aeab7a6 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceVar.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/InferenceVar.java
@@ -9,6 +9,7 @@ import java.util.Collections;
 import java.util.EnumMap;
 import java.util.EnumSet;
 import java.util.LinkedHashSet;
+import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
 import java.util.function.Function;
@@ -149,7 +150,7 @@ public final class InferenceVar implements JTypeMirror, SubstVar {
 
 
             // put the new bounds before updating
-            LinkedHashSet<JTypeMirror> newBounds = new LinkedHashSet<>();
+            Set<JTypeMirror> newBounds = new LinkedHashSet<>();
             boundSet.bounds.put(kind, newBounds);
 
             for (JTypeMirror prev : prevBounds) {
@@ -335,7 +336,7 @@ public final class InferenceVar implements JTypeMirror, SubstVar {
     private static final class BoundSet {
 
         JTypeMirror inst;
-        EnumMap<BoundKind, Set<JTypeMirror>> bounds = new EnumMap<>(BoundKind.class);
+        Map<BoundKind, Set<JTypeMirror>> bounds = new EnumMap<>(BoundKind.class);
 
     }
 }
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/PhaseOverloadSet.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/PhaseOverloadSet.java
index f57e57e563..d8876cbbb9 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/PhaseOverloadSet.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/PhaseOverloadSet.java
@@ -243,11 +243,8 @@ final class PhaseOverloadSet extends OverloadSet<MethodCtDecl> {
 
         JTypeMirror rs = sfun.getReturnType();
         JTypeMirror rt = tfun.getReturnType();
-        if (TypeOps.mentionsAny(rs, sparams) && !ctx.isGround(rt)) {
-            return false;
-        }
-
-        return addGenericExprConstraintsRecursive(ctx, ei, rs, rt, tToS, site);
+        return (!TypeOps.mentionsAny(rs, sparams) || ctx.isGround(rt))
+            && addGenericExprConstraintsRecursive(ctx, ei, rs, rt, tToS, site);
     }
 
     private boolean addGenericExprConstraintsRecursive(InferenceContext ctx, ExprMirror ei, JTypeMirror rs, JTypeMirror rt, Substitution tToS, MethodCallSite site) {
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/TypeInferenceLogger.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/TypeInferenceLogger.java
index aef5b99fa3..a21945cb0b 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/TypeInferenceLogger.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/TypeInferenceLogger.java
@@ -6,9 +6,10 @@
 package net.sourceforge.pmd.lang.java.types.internal.infer;
 
 import java.io.PrintStream;
+import java.util.ArrayDeque;
+import java.util.Deque;
 import java.util.Iterator;
 import java.util.List;
-import java.util.Stack;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -317,7 +318,7 @@ public interface TypeInferenceLogger {
     class VerboseLogger extends SimpleLogger {
 
 
-        private final Stack<Integer> marks = new Stack<>();
+        private final Deque<Integer> marks = new ArrayDeque<>();
 
         public VerboseLogger(PrintStream out) {
             super(out);
diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/ast/LambdaMirrorImpl.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/ast/LambdaMirrorImpl.java
index ddf7e61f2b..51a4663079 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/ast/LambdaMirrorImpl.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/types/internal/infer/ast/LambdaMirrorImpl.java
@@ -112,11 +112,7 @@ class LambdaMirrorImpl extends BaseFunctionalMirror<ASTLambdaExpression> impleme
     @Override
     public boolean isValueCompatible() {
         ASTBlock block = myNode.getBlock();
-        if (block == null) {
-            return true;
-        } else {
-            return isLambdaBodyCompatible(block, false);
-        }
+        return block == null || isLambdaBodyCompatible(block, false);
     }
 
     @Override