equals和==区别

马如林

于 2008-04-22 12:36:00 发布

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分类专栏： JavaEE等文章标签： equals returning function java basic object

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本文探讨了Java中比较对象时，equals方法与==运算符的区别。==检查两个对象的内存引用是否相同，而equals方法旨在判断逻辑上的等价性。通过示例代码展示当使用equals和==时，不同情况下ArrayList的比较结果。

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总是被问，其实看完下面的话就明白很多：
One of the most common gotchas for beginning Java programmers involves comparing Objects, especially Strings, with the == operator. Every Object in Java has a unique location in the Java Virtual Machine's memory. The == operator returns true if the two handles on the left and right sides refer to the same location in memory. The function Object.equals() is intended to return true if two handles refer to logically equivalent instances. In the most basic case, this function works by comparing the value of each of the data fields of the two instances and returning true only if they're all equivalent. You should override Object.equals() in your own classes to provide more robust logic:

大概的意思就是是否内存指向同一对象，==是物理上是否相等，而 equals则是逻辑上是否相等。