Split off generation of equals() and hashCode() methods form @DaTa into a new annotation, @EqualsAndHashCode.

Addresses issue #8

Author: Reinier Zwitserloot

src/lombok/EqualsAndHashCode.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright © 2009 Reinier Zwitserloot and Roel Spilker.
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package lombok;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Generates implementations for the <code>equals</code> and <code>hashCode</code> methods inherited by all objects.
+ * <p>
+ * If either method already exists, then <code>&#64;EqualsAndHashCode</code> will not generate that particular method.
+ * If they all exist, <code>&#64;EqualsAndHashCode</code> generates no methods, and emits a warning instead to highlight
+ * that its doing nothing at all. The parameter list and return type are not relevant when deciding to skip generation of
+ * a method; any method named <code>hashCode</code> will make <code>&#64;EqualsAndHashCode</code> not generate that method,
+ * for example.
+ * <p>
+ * All fields that are non-static and non-transient are used in the equality check and hashCode generation. You can exclude
+ * more fields by specifying them in the <code>exclude</code> parameter.
+ * <p>
+ * Normally, auto-generating <code>hashCode</code> and <code>equals</code> implementations in a subclass is a bad idea, as
+ * the superclass also defines fields, for which equality checks/hashcodes won't be auto-generated. Therefore, a warning
+ * is emitted when you try. Instead, you can set the <code>callSuper</code> parameter to <em>true</em> which will call
+ * <code>super.equals</code> and <code>super.hashCode</code>. Doing this with <code>java.lang.Object</code> as superclass is
+ * pointless, so, conversely, setting this flag when <em>NOT</em> extending something (other than Object) will also generate
+ * a warning. Be aware that not all implementations of <code>equals</code> correctly handle being called from a subclass!
+ * Fortunately, lombok-generated <code>equals</code> implementations do correctly handle it.
+ * <p>
+ * Array fields are handled by way of {@link java.util.Arrays#deepEquals(Object[], Object[])} where necessary, as well
+ * as <code>deepHashCode</code>. The downside is that arrays with circular references (arrays that contain themselves,
+ * possibly indirectly) results in calls to <code>hashCode</code> and <code>equals</code> throwing a
+ * {@link java.lang.StackOverflowError}. However, the implementations for java's own {@link java.util.ArrayList} suffer
+ * from the same flaw.
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.SOURCE)
+public @interface EqualsAndHashCode {
+	/**
+	 * Any fields listed here will not be taken into account in the generated
+	 * <code>equals</code> and <code>hashCode</code> implementations.
+	 */
+	String[] exclude() default {};
+	
+	/**
+	 * Call on the superclass's implementations of <code>equals</code> and <code>hashCode</code> before calculating
+	 * for the fields in this class.
+	 */
+	boolean callSuper() default false;
+}