The hashCode() method now generates a magic prime instead of 0 for the hash of null values; this reduces collisions.

doc/changelog.markdown

@@ -4,6 +4,7 @@ Lombok Changelog
 ### v1.16.5 "Edgy Guinea Pig"
 * BUGFIX: Parameterized static methods with `@Builder` would produce compiler errors in javac. [Issue #793](https://code.google.com/p/projectlombok/issues/detail?id=793).
 * PERFORMANCE: the config system caused significant slowdowns in eclipse if the filesystem is very slow (network file system) or has a slow authentication system.
+* FEATURE: the `hashCode()` method generated by lombok via `@EqualsAndHashCode`, `@Data`, and `@Value` is now smarter about nulls; they are treated as if they hash to a magic prime instead of 0, which reduces hash collisions.
 
 ### v1.16.4 (April 14th, 2015)
 * BUGFIX: Lombok now works with Eclipse Mars.

src/core/lombok/core/handlers/HandlerUtil.java

@@ -68,6 +68,10 @@ public class HandlerUtil {
 		return 97;
 	}
 	
+	public static int primeForNull() {
+		return 43;
+	}
+	
 	/** Checks if the given name is a valid identifier.
 	 * 
 	 * If it is, this returns {@code true} and does nothing else.

src/core/lombok/eclipse/handlers/HandleEqualsAndHashCode.java

@@ -358,7 +358,7 @@ public class HandleEqualsAndHashCode extends EclipseAnnotationHandler<EqualsAndH
 					statements.add(createResultCalculation(source, fieldAccessor));
 				} else /* objects */ {
 					/* final java.lang.Object $fieldName = this.fieldName; */
-					/* $fieldName == null ? 0 : $fieldName.hashCode() */
+					/* $fieldName == null ? NULL_PRIME : $fieldName.hashCode() */
 					statements.add(createLocalDeclaration(source, dollarFieldName, generateQualifiedTypeRef(source, TypeConstants.JAVA_LANG_OBJECT), fieldAccessor));
 					
 					SingleNameReference copy1 = new SingleNameReference(dollarFieldName, p);
@@ -375,8 +375,8 @@ public class HandleEqualsAndHashCode extends EclipseAnnotationHandler<EqualsAndH
 					setGeneratedBy(nullLiteral, source);
 					EqualExpression objIsNull = new EqualExpression(copy2, nullLiteral, OperatorIds.EQUAL_EQUAL);
 					setGeneratedBy(objIsNull, source);
-					IntLiteral int0 = makeIntLiteral("0".toCharArray(), source);
-					ConditionalExpression nullOrHashCode = new ConditionalExpression(objIsNull, int0, hashCodeCall);
+					IntLiteral intMagic = makeIntLiteral(String.valueOf(HandlerUtil.primeForNull()).toCharArray(), source);
+					ConditionalExpression nullOrHashCode = new ConditionalExpression(objIsNull, intMagic, hashCodeCall);
 					nullOrHashCode.sourceStart = pS; nullOrHashCode.sourceEnd = pE;
 					setGeneratedBy(nullOrHashCode, source);
 					statements.add(createResultCalculation(source, nullOrHashCode));

src/core/lombok/javac/handlers/HandleEqualsAndHashCode.java

@@ -307,7 +307,7 @@ public class HandleEqualsAndHashCode extends JavacAnnotationHandler<EqualsAndHas
 				statements.append(createResultCalculation(typeNode, maker.Apply(List.<JCExpression>nil(), hcMethod, List.of(fieldAccessor))));
 			} else /* objects */ {
 				/* final java.lang.Object $fieldName = this.fieldName; */
-				/* $fieldName == null ? 0 : $fieldName.hashCode() */
+				/* $fieldName == null ? NULL_PRIME : $fieldName.hashCode() */
 				
 				Name dollarFieldName = dollar.append(((JCVariableDecl)fieldNode.get()).name);
 				statements.append(maker.VarDef(maker.Modifiers(finalFlag), dollarFieldName, genJavaLangTypeRef(typeNode, "Object"), fieldAccessor));
@@ -315,7 +315,7 @@ public class HandleEqualsAndHashCode extends JavacAnnotationHandler<EqualsAndHas
 				JCExpression hcCall = maker.Apply(List.<JCExpression>nil(), maker.Select(maker.Ident(dollarFieldName), typeNode.toName("hashCode")),
 						List.<JCExpression>nil());
 				JCExpression thisEqualsNull = maker.Binary(CTC_EQUAL, maker.Ident(dollarFieldName), maker.Literal(CTC_BOT, null));
-				statements.append(createResultCalculation(typeNode, maker.Conditional(thisEqualsNull, maker.Literal(0), hcCall)));
+				statements.append(createResultCalculation(typeNode, maker.Conditional(thisEqualsNull, maker.Literal(HandlerUtil.primeForNull()), hcCall)));
 			}
 		}
 		

test/transform/resource/after-delombok/Accessors.java

@@ -100,7 +100,7 @@ class AccessorsPrefix3 {
 		final int PRIME = 59;
 		int result = 1;
 		final java.lang.Object $fName = this.getName();
-		result = result * PRIME + ($fName == null ? 0 : $fName.hashCode());
+		result = result * PRIME + ($fName == null ? 43 : $fName.hashCode());
 		return result;
 	}
 }

test/transform/resource/after-delombok/DataOnLocalClass.java

@@ -50,7 +50,7 @@ class DataOnLocalClass1 {
 				int result = 1;
 				result = result * PRIME + this.getX();
 				final java.lang.Object $name = this.getName();
-				result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+				result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 				return result;
 			}
 			@java.lang.Override
@@ -116,7 +116,7 @@ class DataOnLocalClass2 {
 					final int PRIME = 59;
 					int result = 1;
 					final java.lang.Object $name = this.getName();
-					result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+					result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 					return result;
 				}
 				@java.lang.Override

test/transform/resource/after-delombok/DataPlain.java

@@ -49,7 +49,7 @@ class Data1 {
 		int result = 1;
 		result = result * PRIME + this.getX();
 		final java.lang.Object $name = this.getName();
-		result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+		result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 		return result;
 	}
 	@java.lang.Override
@@ -110,7 +110,7 @@ class Data2 {
 		int result = 1;
 		result = result * PRIME + this.getX();
 		final java.lang.Object $name = this.getName();
-		result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+		result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 		return result;
 	}
 	@java.lang.Override
@@ -165,7 +165,7 @@ final class Data3 {
 		int result = 1;
 		result = result * PRIME + this.getX();
 		final java.lang.Object $name = this.getName();
-		result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+		result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 		return result;
 	}
 	@java.lang.Override

test/transform/resource/after-delombok/DataWithGetter.java

@@ -47,7 +47,7 @@ class DataWithGetter {
 		result = result * PRIME + this.getX();
 		result = result * PRIME + this.getY();
 		final java.lang.Object $z = this.getZ();
-		result = result * PRIME + ($z == null ? 0 : $z.hashCode());
+		result = result * PRIME + ($z == null ? 43 : $z.hashCode());
 		return result;
 	}
 	@java.lang.Override

test/transform/resource/after-delombok/DataWithGetterNone.java

@@ -47,7 +47,7 @@ class DataWithGetterNone {
 		result = result * PRIME + this.x;
 		result = result * PRIME + this.y;
 		final java.lang.Object $z = this.z;
-		result = result * PRIME + ($z == null ? 0 : $z.hashCode());
+		result = result * PRIME + ($z == null ? 43 : $z.hashCode());
 		return result;
 	}
 	@java.lang.Override

test/transform/resource/after-delombok/EqualsAndHashCode.java

@@ -38,9 +38,9 @@ class EqualsAndHashCode {
 		result = result * PRIME + java.util.Arrays.hashCode(this.y);
 		result = result * PRIME + java.util.Arrays.deepHashCode(this.z);
 		final java.lang.Object $a = this.a;
-		result = result * PRIME + ($a == null ? 0 : $a.hashCode());
+		result = result * PRIME + ($a == null ? 43 : $a.hashCode());
 		final java.lang.Object $b = this.b;
-		result = result * PRIME + ($b == null ? 0 : $b.hashCode());
+		result = result * PRIME + ($b == null ? 43 : $b.hashCode());
 		return result;
 	}
 }

test/transform/resource/after-delombok/EqualsAndHashCodeWithOnParam.java

@@ -41,9 +41,9 @@ class EqualsAndHashCodeWithOnParam {
 		result = result * PRIME + java.util.Arrays.hashCode(this.y);
 		result = result * PRIME + java.util.Arrays.deepHashCode(this.z);
 		final java.lang.Object $a = this.a;
-		result = result * PRIME + ($a == null ? 0 : $a.hashCode());
+		result = result * PRIME + ($a == null ? 43 : $a.hashCode());
 		final java.lang.Object $b = this.b;
-		result = result * PRIME + ($b == null ? 0 : $b.hashCode());
+		result = result * PRIME + ($b == null ? 43 : $b.hashCode());
 		return result;
 	}
 }

test/transform/resource/after-delombok/GetterLazyEahcToString.java

@@ -34,9 +34,9 @@ class GetterLazyEahcToString {
 		final int PRIME = 59;
 		int result = 1;
 		final java.lang.Object $value = this.getValue();
-		result = result * PRIME + ($value == null ? 0 : $value.hashCode());
+		result = result * PRIME + ($value == null ? 43 : $value.hashCode());
 		final java.lang.Object $value2 = this.value2;
-		result = result * PRIME + ($value2 == null ? 0 : $value2.hashCode());
+		result = result * PRIME + ($value2 == null ? 43 : $value2.hashCode());
 		return result;
 	}
 	

test/transform/resource/after-delombok/ValuePlain.java

@@ -39,7 +39,7 @@ final class Value1 {
 		int result = 1;
 		result = result * PRIME + this.getX();
 		final java.lang.Object $name = this.getName();
-		result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+		result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 		return result;
 	}
 	@java.lang.Override
@@ -96,7 +96,7 @@ class Value2 {
 		int result = 1;
 		result = result * PRIME + this.getX();
 		final java.lang.Object $name = this.getName();
-		result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+		result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 		return result;
 	}
 	@java.lang.Override

test/transform/resource/after-ecj/Accessors.java

@@ -93,7 +93,7 @@ class AccessorsChain {
     final int PRIME = 59;
     int result = 1;
     final java.lang.Object $fName = this.getName();
-    result = ((result * PRIME) + (($fName == null) ? 0 : $fName.hashCode()));
+    result = ((result * PRIME) + (($fName == null) ? 43 : $fName.hashCode()));
     return result;
   }
 }

test/transform/resource/after-ecj/DataOnLocalClass.java

@@ -40,7 +40,7 @@ class DataOnLocalClass1 {
         int result = 1;
         result = ((result * PRIME) + this.getX());
         final java.lang.Object $name = this.getName();
-        result = ((result * PRIME) + (($name == null) ? 0 : $name.hashCode()));
+        result = ((result * PRIME) + (($name == null) ? 43 : $name.hashCode()));
         return result;
       }
       public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {
@@ -89,7 +89,7 @@ class DataOnLocalClass2 {
           final int PRIME = 59;
           int result = 1;
           final java.lang.Object $name = this.getName();
-          result = ((result * PRIME) + (($name == null) ? 0 : $name.hashCode()));
+          result = ((result * PRIME) + (($name == null) ? 43 : $name.hashCode()));
           return result;
         }
         public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {

test/transform/resource/after-ecj/DataPlain.java

@@ -35,7 +35,7 @@ import lombok.Data;
     int result = 1;
     result = ((result * PRIME) + this.getX());
     final java.lang.Object $name = this.getName();
-    result = ((result * PRIME) + (($name == null) ? 0 : $name.hashCode()));
+    result = ((result * PRIME) + (($name == null) ? 43 : $name.hashCode()));
     return result;
   }
   public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {
@@ -82,7 +82,7 @@ import lombok.Data;
     int result = 1;
     result = ((result * PRIME) + this.getX());
     final java.lang.Object $name = this.getName();
-    result = ((result * PRIME) + (($name == null) ? 0 : $name.hashCode()));
+    result = ((result * PRIME) + (($name == null) ? 43 : $name.hashCode()));
     return result;
   }
   public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {
@@ -124,7 +124,7 @@ final @Data class Data3 {
     int result = 1;
     result = ((result * PRIME) + this.getX());
     final java.lang.Object $name = this.getName();
-    result = ((result * PRIME) + (($name == null) ? 0 : $name.hashCode()));
+    result = ((result * PRIME) + (($name == null) ? 43 : $name.hashCode()));
     return result;
   }
   public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {

test/transform/resource/after-ecj/DataWithGetter.java

@@ -35,7 +35,7 @@
     result = ((result * PRIME) + this.getX());
     result = ((result * PRIME) + this.getY());
     final java.lang.Object $z = this.getZ();
-    result = ((result * PRIME) + (($z == null) ? 0 : $z.hashCode()));
+    result = ((result * PRIME) + (($z == null) ? 43 : $z.hashCode()));
     return result;
   }
   public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {

test/transform/resource/after-ecj/DataWithGetterNone.java

@@ -35,7 +35,7 @@
     result = ((result * PRIME) + this.x);
     result = ((result * PRIME) + this.y);
     final java.lang.Object $z = this.z;
-    result = ((result * PRIME) + (($z == null) ? 0 : $z.hashCode()));
+    result = ((result * PRIME) + (($z == null) ? 43 : $z.hashCode()));
     return result;
   }
   public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {

test/transform/resource/after-ecj/EqualsAndHashCode.java

@@ -41,9 +41,9 @@
     result = ((result * PRIME) + java.util.Arrays.hashCode(this.y));
     result = ((result * PRIME) + java.util.Arrays.deepHashCode(this.z));
     final java.lang.Object $a = this.a;
-    result = ((result * PRIME) + (($a == null) ? 0 : $a.hashCode()));
+    result = ((result * PRIME) + (($a == null) ? 43 : $a.hashCode()));
     final java.lang.Object $b = this.b;
-    result = ((result * PRIME) + (($b == null) ? 0 : $b.hashCode()));
+    result = ((result * PRIME) + (($b == null) ? 43 : $b.hashCode()));
     return result;
   }
 }

test/transform/resource/after-ecj/EqualsAndHashCodeWithOnParam.java

@@ -44,9 +44,9 @@
     result = ((result * PRIME) + java.util.Arrays.hashCode(this.y));
     result = ((result * PRIME) + java.util.Arrays.deepHashCode(this.z));
     final java.lang.Object $a = this.a;
-    result = ((result * PRIME) + (($a == null) ? 0 : $a.hashCode()));
+    result = ((result * PRIME) + (($a == null) ? 43 : $a.hashCode()));
     final java.lang.Object $b = this.b;
-    result = ((result * PRIME) + (($b == null) ? 0 : $b.hashCode()));
+    result = ((result * PRIME) + (($b == null) ? 43 : $b.hashCode()));
     return result;
   }
 }

test/transform/resource/after-ecj/GetterLazyEahcToString.java

@@ -49,9 +49,9 @@
     final int PRIME = 59;
     int result = 1;
     final java.lang.Object $value = this.getValue();
-    result = ((result * PRIME) + (($value == null) ? 0 : $value.hashCode()));
+    result = ((result * PRIME) + (($value == null) ? 43 : $value.hashCode()));
     final java.lang.Object $value2 = this.value2;
-    result = ((result * PRIME) + (($value2 == null) ? 0 : $value2.hashCode()));
+    result = ((result * PRIME) + (($value2 == null) ? 43 : $value2.hashCode()));
     return result;
   }
   public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {

test/transform/resource/after-ecj/ValuePlain.java

@@ -27,7 +27,7 @@ final @lombok.Value class Value1 {
     int result = 1;
     result = ((result * PRIME) + this.getX());
     final java.lang.Object $name = this.getName();
-    result = ((result * PRIME) + (($name == null) ? 0 : $name.hashCode()));
+    result = ((result * PRIME) + (($name == null) ? 43 : $name.hashCode()));
     return result;
   }
   public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {
@@ -72,7 +72,7 @@ final @lombok.Value class Value1 {
     int result = 1;
     result = ((result * PRIME) + this.getX());
     final java.lang.Object $name = this.getName();
-    result = ((result * PRIME) + (($name == null) ? 0 : $name.hashCode()));
+    result = ((result * PRIME) + (($name == null) ? 43 : $name.hashCode()));
     return result;
   }
   public @java.lang.Override @java.lang.SuppressWarnings("all") @javax.annotation.Generated("lombok") java.lang.String toString() {

usage_examples/DataExample_post.jpage

@@ -62,7 +62,7 @@ public class DataExample {
 		final int PRIME = 59;
 		int result = 1;
 		final long temp1 = Double.doubleToLongBits(this.getScore());
-		result = (result*PRIME) + (this.getName() == null ? 0 : this.getName().hashCode());
+		result = (result*PRIME) + (this.getName() == null ? 43 : this.getName().hashCode());
 		result = (result*PRIME) + this.getAge();
 		result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
 		result = (result*PRIME) + Arrays.deepHashCode(this.getTags());
@@ -111,8 +111,8 @@ public class DataExample {
 		@Override public int hashCode() {
 			final int PRIME = 59;
 			int result = 1;
-			result = (result*PRIME) + (this.getName() == null ? 0 : this.getName().hashCode());
-			result = (result*PRIME) + (this.getValue() == null ? 0 : this.getValue().hashCode());
+			result = (result*PRIME) + (this.getName() == null ? 43 : this.getName().hashCode());
+			result = (result*PRIME) + (this.getValue() == null ? 43 : this.getValue().hashCode());
 			return result;
 		}
 	}

usage_examples/EqualsAndHashCodeExample_post.jpage

@@ -27,7 +27,7 @@ public class EqualsAndHashCodeExample {
 		final int PRIME = 59;
 		int result = 1;
 		final long temp1 = Double.doubleToLongBits(this.score);
-		result = (result*PRIME) + (this.name == null ? 0 : this.name.hashCode());
+		result = (result*PRIME) + (this.name == null ? 43 : this.name.hashCode());
 		result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));
 		result = (result*PRIME) + Arrays.deepHashCode(this.tags);
 		return result;

usage_examples/ValueExample_post.jpage

@@ -49,7 +49,7 @@ public final class ValueExample {
 		final int PRIME = 59;
 		int result = 1;
 		final Object $name = this.getName();
-		result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+		result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 		result = result * PRIME + this.getAge();
 		final long $score = Double.doubleToLongBits(this.getScore());
 		result = result * PRIME + (int)($score >>> 32 ^ $score);
@@ -106,9 +106,9 @@ public final class ValueExample {
 			final int PRIME = 59;
 			int result = 1;
 			final Object $name = this.getName();
-			result = result * PRIME + ($name == null ? 0 : $name.hashCode());
+			result = result * PRIME + ($name == null ? 43 : $name.hashCode());
 			final Object $value = this.getValue();
-			result = result * PRIME + ($value == null ? 0 : $value.hashCode());
+			result = result * PRIME + ($value == null ? 43 : $value.hashCode());
 			return result;
 		}