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POGeneric reflective helper method for equals and hashCode
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copied!<p>I'm thinking about to create a reflective helper method for equals and hashCode. </p> <ul> <li>In case of equals the helper method looks over the reflection API to the fields of objectA and compares them with fields of objectB.</li> <li>In case of hashCode the helper method looks over the reflection API to the fields and calculates a hashCode in a iteration loop.</li> </ul> <p>The good thing is that I don't to be worry about missing fields in my equals or hashCode implementation. The bad thing is I guess performance. What do you think about this idea? Please share your opinion!</p> <p>This is my first draft for equals:</p> <pre><code>public final class ReflectiveEqualsHelper { public static boolean isEqual(final Object a, final Object b) { if (!isTypeEqual(a, b)) { return false; } Field[] fields = getFields(a); Object valueA; Object valueB; String fieldName; for (int i = 0; i < fields.length; i++) { fieldName = fields[i].getName(); valueA = getValueByFieldName(a, fieldName); valueB = getValueByFieldName(b, fieldName); if (!compare(valueA, valueB)) { return false; } } return true; } @SuppressWarnings("rawtypes") private static Field[] getFields(final Object o) { Class clazz = o.getClass(); Field[] fields = clazz.getDeclaredFields(); return fields; } private static Field getField(final Object o, final String name) { try { Field field = o.getClass().getDeclaredField(name); return field; } catch (NoSuchFieldException e) { throw new RuntimeException(e); } } private static Object getValueByFieldName(final Object o, final String name) { Field field = getField(o, name); field.setAccessible(true); try { Object value = field.get(o); field.setAccessible(false); return value; } catch (IllegalAccessException e) { throw new RuntimeException(e); } } private static boolean areBothNull(final Object a, final Object b) { return (a == null && b == null); } private static boolean isTypeEqual(final Object a, final Object b) { if (areBothNull(a, b)) { return false; } return a.getClass().equals(b.getClass()); } private static boolean compare(final Object a, final Object b) { if (a == null) { return false; } else if (b == null) { return false; } return a.equals(b); } </code></pre> <p>}</p> <pre><code>public class ReflectiveEqualsHelperTest { @Test public void testIsEqual() { Vector a = new Vector(Long.valueOf(1L), 3L); Vector b = new Vector(Long.valueOf(1L), 3L); Vector c = new Vector(Long.valueOf(2L), 3L); boolean testA = ReflectiveEqualsHelper.isEqual(a, b); boolean testB = ReflectiveEqualsHelper.isEqual(a, c); boolean testC = ReflectiveEqualsHelper.isEqual(b, c); assertTrue(testA); assertFalse(testB); assertFalse(testC); } class Vector { public static final int STATIC = 1; private Long x; private long y; public Vector(Long x, long y) { super(); this.x = x; this.y = y; } public Long getX() { return x; } public void setX(Long x) { this.x = x; } public long getY() { return y; } public void setY(long y) { this.y = y; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((x == null) ? 0 : x.hashCode()); result = prime * result + (int) (y ^ (y >>> 32)); return result; } @Override public boolean equals(Object obj) { if (this == obj) { return true; } return ReflectiveEqualsHelper.isEqual(this, obj); } } </code></pre> <p>}</p> <p>Cheers, Kevin</p>

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