Boxing and Unboxing

请预测下面程序运行的结果：

package com.test;public class Test {public static void main(String[] args) {int i = 6;Integer test1 = i;Integer test2 = i;if (test1 == test2) {System.out.println("True");}else {System.out.println("False");}int j = 9999;test1 = j;test2 = j;if (test1 == test2) {System.out.println("True");}else {System.out.println("False");}}} 

 

正确结果是：

True

False

 

你“目测”的结果对吗？

 

至于原因情况下面的这段E文解释：

A further subtlety is that boxed values may be cached. Caching is required when boxing an int or short value between -128 and 127, a char value between '/u0000' and '/u007f', a byte, or a boolean; and caching is permitted when boxing other values. This is because 6 is smaller than 128, so boxing the value 6 always returns exactly the same object.

 

Even for small values, for which == will compare values of type Integer correctly, we recommend against its use. It is clearer and cleaner to use equals rather than == to compare values of reference type, such as Integer or String.