### Eclipse Workspace Patch 1.0
#P org.eclipse.jdt.core
Index: compiler/org/eclipse/jdt/internal/compiler/ast/InstanceOfExpression.java
===================================================================
RCS file: /cvsroot/eclipse/org.eclipse.jdt.core/compiler/org/eclipse/jdt/internal/compiler/ast/InstanceOfExpression.java,v
retrieving revision 1.59
diff -u -r1.59 InstanceOfExpression.java
--- compiler/org/eclipse/jdt/internal/compiler/ast/InstanceOfExpression.java	7 Mar 2009 01:08:07 -0000	1.59
+++ compiler/org/eclipse/jdt/internal/compiler/ast/InstanceOfExpression.java	12 Mar 2010 10:33:31 -0000
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2009 IBM Corporation and others.
+ * Copyright (c) 2000, 2010 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
@@ -32,12 +32,12 @@
 public FlowInfo analyseCode(BlockScope currentScope, FlowContext flowContext, FlowInfo flowInfo) {
 	LocalVariableBinding local = this.expression.localVariableBinding();
 	if (local != null && (local.type.tagBits & TagBits.IsBaseType) == 0) {
-		flowContext.recordUsingNullReference(currentScope, local,
-			this.expression, FlowContext.CAN_ONLY_NULL | FlowContext.IN_INSTANCEOF, flowInfo);
 		flowInfo = this.expression.analyseCode(currentScope, flowContext, flowInfo).
 			unconditionalInits();
 		FlowInfo initsWhenTrue = flowInfo.copy();
 		initsWhenTrue.markAsComparedEqualToNonNull(local);
+		flowContext.recordUsingNullReference(currentScope, local,
+				this.expression, FlowContext.CAN_ONLY_NULL | FlowContext.IN_INSTANCEOF, flowInfo);
 		// no impact upon enclosing try context
 		return FlowInfo.conditional(initsWhenTrue, flowInfo.copy());
 	}
#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 1.94
diff -u -r1.94 NullReferenceTest.java
--- src/org/eclipse/jdt/core/tests/compiler/regression/NullReferenceTest.java	3 Mar 2010 18:37:13 -0000	1.94
+++ src/org/eclipse/jdt/core/tests/compiler/regression/NullReferenceTest.java	12 Mar 2010 10:34:53 -0000
@@ -11636,4 +11636,30 @@
 		"    12  return\n";
 	checkDisassembledClassFile(OUTPUT_DIR + File.separator + "X.class", "X", expectedOutput);
 }
+
+// https://bugs.eclipse.org/bugs/show_bug.cgi?id=305590
+// To verify that a "instanceof always yields false" warning is not elicited in the
+// case when the expression has been assigned a non null value in the instanceof check.
+public void testBug305590() {
+	runNegativeTest(
+		new String[] {
+			"X.java",
+			"public class X {\n" +
+			"  public void foo() {\n" +
+			"	 Object str = null;\n" +
+			"	 if ((str = \"str\") instanceof String) {}\n" + // shouldn't warn
+			"	 str = null;\n" +
+			"	 if ((str = \"str\") instanceof Number) {}\n" + // shouldn't warn
+			"	 str = null;\n" +
+			"	 if (str instanceof String) {}\n" + // should warn
+			"  }\n" +
+			"}"},
+		"----------\n" +
+		"1. ERROR in X.java (at line 8)\n" + 
+		"	if (str instanceof String) {}\n" + 
+		"	    ^^^\n" + 
+		"instanceof always yields false: The variable str can only be null at this location\n" + 
+		"----------\n",
+	    JavacTestOptions.Excuse.EclipseWarningConfiguredAsError);
+}
 }
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