Boxing and Unboxing

最新推荐文章于 2024-07-19 23:18:37 发布

原创最新推荐文章于 2024-07-19 23:18:37 发布 · 234 阅读

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CC 4.0 BY-SA版权

文章标签：

#integer #caching #reference #equals #string #byte

本文通过一个简单的Java程序示例，探讨了整数装箱过程中利用缓存机制的特点，特别是对于小范围整数值的处理方式。文章揭示了当整数值位于-128到127之间时，其装箱后的Integer对象会复用已有的实例，而超出这个范围则不会共享同一对象。

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.