### Eclipse Workspace Patch 1.0
#P org.eclipse.jdt.core
Index: compiler/org/eclipse/jdt/internal/compiler/ast/CompoundAssignment.java
===================================================================
RCS file: /cvsroot/eclipse/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/CompoundAssignment.java,v
retrieving revision 1.60
diff -u -r1.60 CompoundAssignment.java
--- compiler/org/eclipse/jdt/internal/compiler/ast/CompoundAssignment.java	22 Jul 2009 17:08:54 -0000	1.60
+++ compiler/org/eclipse/jdt/internal/compiler/ast/CompoundAssignment.java	9 Mar 2011 09:41:15 -0000
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2009 IBM Corporation and others.
+ * Copyright (c) 2000, 2011 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -42,7 +42,18 @@
 	if (this.resolvedType.id != T_JavaLangString) {
 		this.lhs.checkNPE(currentScope, flowContext, flowInfo);
 	}
-	return  ((Reference) this.lhs).analyseAssignment(currentScope, flowContext, flowInfo, this, true).unconditionalInits();
+	flowInfo = ((Reference) this.lhs).analyseAssignment(currentScope, flowContext, flowInfo, this, true).unconditionalInits();
+	if (this.resolvedType.id == T_JavaLangString) {
+		// https://bugs.eclipse.org/bugs/show_bug.cgi?id=339250
+		LocalVariableBinding local = this.lhs.localVariableBinding();
+		if (local != null && this.resolvedType.id == T_JavaLangString) {
+			// compound assignment results in a definitely non null value for String
+			flowInfo.markAsDefinitelyNonNull(local);
+			if (flowContext.initsOnFinally != null)
+				flowContext.initsOnFinally.markAsDefinitelyNonNull(local);
+		}
+	}
+	return flowInfo;
 }
 
 	public boolean checkCastCompatibility() {
#P org.eclipse.jdt.core.tests.compiler
Index: src/org/eclipse/jdt/core/tests/compiler/regression/NullReferenceTest.java
===================================================================
RCS file: /cvsroot/eclipse/org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/NullReferenceTest.java,v
retrieving revision 1.117
diff -u -r1.117 NullReferenceTest.java
--- src/org/eclipse/jdt/core/tests/compiler/regression/NullReferenceTest.java	5 Mar 2011 17:18:31 -0000	1.117
+++ src/org/eclipse/jdt/core/tests/compiler/regression/NullReferenceTest.java	9 Mar 2011 09:41:18 -0000
@@ -44,7 +44,7 @@
 // Only the highest compliance level is run; add the VM argument
 // -Dcompliance=1.4 (for example) to lower it if needed
 static {
-//		TESTS_NAMES = new String[] { "testBug336428e" };
+//		TESTS_NAMES = new String[] { "testBug339250" };
 //		TESTS_NUMBERS = new int[] { 561 };
 //		TESTS_RANGE = new int[] { 1, 2049 };
 }
@@ -14441,4 +14441,93 @@
 		"    17  return\n";
 	checkDisassembledClassFile(OUTPUT_DIR + File.separator + "X.class", "X", expectedOutput);
 }
+// https://bugs.eclipse.org/bugs/show_bug.cgi?id=339250
+// Check code gen
+public void testBug339250() throws Exception {
+	Map options = getCompilerOptions();
+	options.put(CompilerOptions.OPTION_ReportRedundantNullCheck, CompilerOptions.WARNING);
+	this.runConformTest(
+		new String[] {
+			"X.java",
+			"public class X {\n" + 
+			"	public static void main(String[] args) {\n" + 
+			"		String s = null;\n" +
+			"		s += \"correctly\";\n" +
+			"		if (s != null) {\n" + 	// s cannot be null
+			"			System.out.println(\"It works \" + s);\n" + 
+			"		}\n" +
+			"	}\n" + 
+			"}",
+		},
+		"It works nullcorrectly",
+		null,
+		true,
+		null,
+		options,
+		null);
+}
+// https://bugs.eclipse.org/bugs/show_bug.cgi?id=339250
+// Check that the redundant null check warning is correctly produced
+public void testBug339250a() throws Exception {
+	this.runNegativeTest(
+		new String[] {
+			"X.java",
+			"public class X {\n" + 
+			"	public static void main(String[] args) {\n" + 
+			"		String s = null;\n" +
+			"		s += \"correctly\";\n" +
+			"		if (s != null) {\n" + 	// s cannot be null
+			"			System.out.println(\"It works \" + s);\n" + 
+			"		}\n" +
+			"	}\n" + 
+			"}",
+		},
+		"----------\n" + 
+		"1. ERROR in X.java (at line 5)\n" + 
+		"	if (s != null) {\n" + 
+		"	    ^\n" + 
+		"Redundant null check: The variable s cannot be null at this location\n" + 
+		"----------\n");
+}
+// https://bugs.eclipse.org/bugs/show_bug.cgi?id=339250
+// Check that the redundant null check warning is correctly produced
+public void testBug339250b() throws Exception {
+	this.runNegativeTest(
+		new String[] {
+			"X.java",
+			"public class X {\n" + 
+			"	public static void main(String[] args) {\n" + 
+			"		String s = null;\n" +
+			"		s += null;\n" +
+			"		if (s != null) {\n" + 	// s is definitely not null
+			"			System.out.println(\"It works \" + s);\n" + 
+			"	    }\n" + 
+			"		s = null;\n" +
+			"		if (s != null) {\n" + 	// s is definitely null
+			"			System.out.println(\"Fails \" + s);\n" + 
+			"	    } else {\n" + 
+			"			System.out.println(\"Works second time too \" + s);\n" +
+			"       }\n" + 
+			"	}\n" + 
+			"}",
+		},
+		"----------\n" + 
+		"1. ERROR in X.java (at line 5)\n" + 
+		"	if (s != null) {\n" + 
+		"	    ^\n" + 
+		"Redundant null check: The variable s cannot be null at this location\n" + 
+		"----------\n" + 
+		"2. ERROR in X.java (at line 9)\n" + 
+		"	if (s != null) {\n" + 
+		"	    ^\n" + 
+		"Null comparison always yields false: The variable s can only be null at this location\n" + 
+		"----------\n" + 
+		"3. WARNING in X.java (at line 9)\n" + 
+		"	if (s != null) {\n" + 
+		"			System.out.println(\"Fails \" + s);\n" + 
+		"	    } else {\n" + 
+		"	               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n" + 
+		"Dead code\n" + 
+		"----------\n");
+}
 }
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