在 Java 中使用 == 运算符比较包装器对象

2022-01-14 00:00:00 integer wrapper equals operator-keyword java

我正在阅读 Kathy Sierra 和 Bert Bates 的 SCJP Java 6，这本书让我非常困惑.在第 245 页上，他们声明以下代码.

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

我很困惑！当我自己尝试时，您似乎无法使用 == 来比较使用 equals() 方法的相同方式.即使整数变量设置为相同的值(即 10)，使用 == 总是会给我假".我对么?使用 == 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

答案的关键就叫object interning.Java 实习生的数字很小(小于 128)，因此所有 Integer(n) 的实例与 n 在实习范围内都是相同的.大于或等于 128 的数字不会被保留，因此 Integer(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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