在Java中使用==运算符来比较包装器对象 [英] Using == operator in Java to compare wrapper objects

问题描述

我正在阅读Kathy Sierra和Bert Bates的SCJP Java 6，这本书让我非常困惑。在页245上，他们说明下面的代码。

I'm reading SCJP Java 6 by Kathy Sierra and Bert Bates and this book is confusing me so much. On page 245 they state that the following code below.

Integer i1 = 1000;
Integer i2 = 1000;
if(i1 != i2)
System.out.println("different objects");

//Prints output
different objects

然后在下一页他们有以下代码

Then on the very next page they have the following code

Integer i3 = 10;
Integer i4 = 10;
if(i3 == i4)
System.out.println("same objects");

//Prints output
same objects

我是如此迷茫！当我自己尝试这个时，似乎你不能使用==来比较你使用equals（）方法的方式。即使整数变量设置为相同的值（即10），使用==总是给我'假'。我对么？使用==来比较相同的Integer对象（具有相同的值）将始终导致'false'

I'm so confused! When I try this out on my own it seems that you cannot use the == to compare the same way you would use equals() method. Using the == always gives me 'false' even if the Integer variables are set to the same value (i.e. 10). Am I correct? Using the == to compare the same Integer object (with same values) will always result in 'false'

推荐答案

关键是答案称为对象实习。 Java实习小数（小于128），因此所有 Integer（n）的实例在实习范围内具有 n 是相同的。大于或等于128的数字不会被实习，因此整数（1000）对象彼此不相等。

The key to the answer is called object interning. Java interns small numbers (less than 128), so all instances of Integer(n) with n in the interned range are the same. Numbers greater than or equal to 128 are not interned, hence Integer(1000) objects are not equal to each other.

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