string comparison: evaluate based on equals comparison (IDEA-160823)

java/java-psi-impl/src/com/intellij/psi/impl/ConstantExpressionVisitor.java

@@ -247,7 +247,7 @@ class ConstantExpressionVisitor extends JavaElementVisitor implements PsiConstan
         value = Boolean.valueOf(((Number)lOperandValue).doubleValue() == ((Number)rOperandValue).doubleValue());
       }
       else if (lOperandValue instanceof String && rOperandValue instanceof String) {
-        value = Boolean.valueOf(lOperandValue == rOperandValue);
+        value = Boolean.valueOf(lOperandValue.equals(rOperandValue));
       }
       else if (lOperandValue instanceof Boolean && rOperandValue instanceof Boolean) {
         value = Boolean.valueOf(((Boolean)lOperandValue).booleanValue() == ((Boolean)rOperandValue).booleanValue());
@@ -260,7 +260,7 @@ class ConstantExpressionVisitor extends JavaElementVisitor implements PsiConstan
         value = Boolean.valueOf(((Number)lOperandValue).doubleValue() != ((Number)rOperandValue).doubleValue());
       }
       else if (lOperandValue instanceof String && rOperandValue instanceof String) {
-        value = Boolean.valueOf(lOperandValue != rOperandValue);
+        value = Boolean.valueOf(!lOperandValue.equals(rOperandValue));
       }
       else if (lOperandValue instanceof Boolean && rOperandValue instanceof Boolean) {
         value = Boolean.valueOf(((Boolean)lOperandValue).booleanValue() != ((Boolean)rOperandValue).booleanValue());

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advHighlighting6/ReachableWhileBodyDueToConstantStringComparison.java

@@ -0,0 +1,43 @@
+
+class Bar {
+  public static final String T = "";
+
+  void m0() {
+    while (T == "") {
+      f();
+    }
+    <error descr="Unreachable statement">f();</error>
+  }
+
+  void m() {
+    while (T == "a") {
+      <error descr="Unreachable statement">f();</error>
+    }
+  }
+
+  void m01() {
+    while (T != "") {
+      <error descr="Unreachable statement">f();</error>
+    }
+  }
+
+  void m1() {
+    while (T != "a") {
+      f();
+    }
+    <error descr="Unreachable statement">f();</error>
+  }
+
+  void m2() {
+    while (T != T) {
+      <error descr="Unreachable statement">f();</error>
+    }
+  }
+
+  void m3() {
+    while (T == T) {}
+    <error descr="Unreachable statement">f();</error>
+  }
+
+  private void f() {}
+}

java/java-tests/testSrc/com/intellij/codeInsight/daemon/LightAdvHighlightingJdk6Test.java

@@ -94,4 +94,8 @@ public class LightAdvHighlightingJdk6Test extends LightDaemonAnalyzerTestCase {
   public void testStaticOnDemandImportResolvesToClass() throws Exception {
     doTest(false, false);
   }
+
+  public void testReachableWhileBodyDueToConstantStringComparison() throws Exception {
+    doTest(false, false);
+  }
 }