Checkout OptionalBool

pmd-core/src/main/java/net/sourceforge/pmd/util/OptionalBool.java

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+/*
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+
+package net.sourceforge.pmd.util;
+
+/** Represents a boolean that may not be present. Use as a non-null type. */
+public enum OptionalBool {
+    YES, NO, UNKNOWN;
+
+    public OptionalBool complement() {
+        switch (this) {
+        case YES: return NO;
+        case NO: return YES;
+        default: return this;
+        }
+    }
+
+    public boolean isKnown() {
+        return this != UNKNOWN;
+    }
+
+    public boolean isTrue() {
+        return this == YES;
+    }
+
+    public static OptionalBool definitely(boolean a) {
+        return a ? YES : NO;
+    }
+}

pmd-core/src/test/java/net/sourceforge/pmd/util/OptionalBoolTest.java

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+/*
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+
+package net.sourceforge.pmd.util;
+
+import static net.sourceforge.pmd.util.OptionalBool.NO;
+import static net.sourceforge.pmd.util.OptionalBool.UNKNOWN;
+import static net.sourceforge.pmd.util.OptionalBool.YES;
+import static net.sourceforge.pmd.util.OptionalBool.definitely;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class OptionalBoolTest {
+
+    @Test
+    public void testDefinitely() {
+        assertEquals(YES, definitely(true));
+        assertEquals(NO, definitely(false));
+    }
+
+    @Test
+    public void testIsKnown() {
+        assertTrue(YES.isKnown());
+        assertTrue(NO.isKnown());
+        assertFalse(UNKNOWN.isKnown());
+    }
+
+    @Test
+    public void testIsTrue() {
+        assertTrue(YES.isTrue());
+        assertFalse(NO.isTrue());
+        assertFalse(UNKNOWN.isTrue());
+    }
+
+    @Test
+    public void testComplement() {
+        assertEquals(YES, NO.complement());
+        assertEquals(NO, YES.complement());
+        assertEquals(UNKNOWN, UNKNOWN.complement());
+    }
+}