null值安全的相等判断

package com.javacodegeeks.snippets.core;import java.util.Arrays;abstract class ObjectUtils {private static final int INITIAL_HASH = 7;private static final int MULTIPLIER = 31;private static final String EMPTY_STRING = "";private static final String NULL_STRING = "null";private static final String ARRAY_START = "{";private static final String ARRAY_END = "}";private static final String EMPTY_ARRAY = ARRAY_START + ARRAY_END;private static final String ARRAY_ELEMENT_SEPARATOR = ", ";/** * Determine if the given objects are equal, returning true if both are null * or false if only one is null. Compares arrays with Arrays.equals, * performing an equality check based on the array elements rather than the * array reference. */public static boolean nullSafeEquals(Object o1, Object o2) {if (o1 == o2) {return true;}if (o1 == null || o2 == null) {return false;}if (o1.equals(o2)) {return true;}if (o1 instanceof Object[] && o2 instanceof Object[]) {return Arrays.equals((Object[]) o1, (Object[]) o2);}if (o1 instanceof boolean[] && o2 instanceof boolean[]) {return Arrays.equals((boolean[]) o1, (boolean[]) o2);}if (o1 instanceof byte[] && o2 instanceof byte[]) {return Arrays.equals((byte[]) o1, (byte[]) o2);}if (o1 instanceof char[] && o2 instanceof char[]) {return Arrays.equals((char[]) o1, (char[]) o2);}if (o1 instanceof double[] && o2 instanceof double[]) {return Arrays.equals((double[]) o1, (double[]) o2);}if (o1 instanceof float[] && o2 instanceof float[]) {return Arrays.equals((float[]) o1, (float[]) o2);}if (o1 instanceof int[] && o2 instanceof int[]) {return Arrays.equals((int[]) o1, (int[]) o2);}if (o1 instanceof long[] && o2 instanceof long[]) {return Arrays.equals((long[]) o1, (long[]) o2);}if (o1 instanceof short[] && o2 instanceof short[]) {return Arrays.equals((short[]) o1, (short[]) o2);}return false;}}class A {public int x;public String str;public A(int x, String str) {this.x = x;this.str = str;}@Overridepublic boolean equals(Object o) {if (o == null) {return false;} else if (o instanceof A) {A obj = (A) o;if (this.x == obj.x && this.str.equals(obj.str)) {return true;}}return false;}}public class NullSafeEquals extends ObjectUtils {public static void main(String[] args) {A a1 = new A(10, "Nikos");A a2 = new A(10, "Dimitrhs");System.out.println(nullSafeEquals(a1, a2));// System.out.println(nullSafeEquals(2,2));// System.out.println(nullSafeEquals(1,"string"));// System.out.println(nullSafeEquals(true,true));}}

运行结果：false

原文：http://examples.javacodegeeks.com/core-java/class/null-safe-equals-method/