[java] InsufficientStringBufferDeclaration: Fix CCE for Character

Fixes #5314

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/performance/InsufficientStringBufferDeclarationRule.java

@@ -240,6 +240,12 @@ public class InsufficientStringBufferDeclarationRule extends AbstractJavaRulecha
 
     private int calculateExpression(ASTExpression expression) {
         Object value = expression.getConstValue();
-        return value == null ? State.UNKNOWN_CAPACITY : (Integer) value;
+        if (value == null) {
+            return State.UNKNOWN_CAPACITY;
+        }
+        if (value instanceof Character) {
+            return (Character) value;
+        }
+        return (Integer) value;
     }
 }

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/performance/xml/InsufficientStringBufferDeclaration.xml

@@ -1419,4 +1419,23 @@ public class LiteralExpression {
 }
         ]]></code>
     </test-code>
+
+    <test-code>
+        <description>#5314 [java] InsufficientStringBufferDeclarationRule: Lack of handling for char type parameters</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+public class StringBufferInstantiationWithCharTest {
+    public void example01() {
+        // misleading instantiation, these buffers
+        // are actually sized to 99 characters long
+        StringBuffer  sb1 = new StringBuffer('c');
+        StringBuilder sb2 = new StringBuilder('c');
+
+        // in these forms, just single characters are allocated
+        StringBuffer  sb3 = new StringBuffer("c");
+        StringBuilder sb4 = new StringBuilder("c");
+    }
+}
+]]></code>
+    </test-code>
 </test-data>