Java中的对象标识哈希码 [英] object identityhashcode in java

问题描述

我有这个问题.

我一直在我的项目中工作(我也在使用EMF Compare).我需要为正在使用的每个对象保留唯一的ID，这就是为什么我决定使用IdentityHashCode的原因，据我了解，此值在编译过程中是相同的.

I've been working in my project (I'm also using EMF Compare). I need to keep an unique ID for each object that I'm using, that's why I decided to use the IdentityHashCode, as far as I understand, this value is the same through the compilation.

我已经在另一个类的方法中将对象作为参数提供，但是当我尝试获取哈希码时，这与打印对象的值时看到的不一样.

I have given the object as a parameter in the method of another class, but when I try to get the hashcode this is not the same that I can see when I print the value of the object.

类似这样的东西:

System.out.println("The Object is: "+obj)

System.out.println("The hash ID is: +Integer.toHexString(System.identityHashCode(obj)));

但是结果我得到了:

对象是:***xxxxxxxxxxxxxx***.EntityImpl@18e588c (name: Comment) has been removed.

哈希ID为:1ec1758

您可以看到两个值完全不同，但是我不明白为什么.到现在为止，我唯一要做的事情(并且可行)是获取对象的String，然后使用substring方法获取18e588c(对于本示例)

As you can see the two values are totally different, but I can't understand why. Until now the only thing that I have done (and it works) is to get the String of the object and then use the substring method to get 18e588c (for this example)

我将不胜感激.

致谢

推荐答案

我需要为正在使用的每个对象保留唯一的ID，这就是为什么我决定使用IdentityHashCode的原因，据我了解，此值在编译过程中是相同的.

I need to keep an unique ID for each object that I'm using, that's why I decided to use the IdentityHashCode, as far as I understand, this value is the same through the compilation.

不.它与编译无关，并且不保证是唯一的.

No. It's got nothing to do with compilation, and it's not guaranteed to be unique.

目前尚不清楚您要做什么，但是您根本不应该将哈希码视为唯一的-不能保证它们是唯一的.

It's not clear what you're trying to do, but you simply shouldn't regard hash codes as unique - they're not guaranteed to be.

Object.hashCode文档指定:

在合理可行的范围内，由Object类定义的hashCode方法确实为不同的对象返回不同的整数.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects.

那与保证它不一样.

您也 被调用toString()的结果所迷惑-我怀疑您的类实际上覆盖了hashCode()，并且Object.toString()调用了可能被覆盖的hashCode()方法，而不是使用身份哈希码:

You're also being confused by the result of calling toString() - I suspect your class actually overrides hashCode(), and Object.toString() calls the potentially-overridden hashCode() method rather than using the identity hash code:

Object类的toString方法返回一个字符串，该字符串包括该对象是其实例的类的名称，符号符'@'和该对象的哈希码的无符号十六进制表示形式.换句话说，此方法返回的字符串等于:

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

getClass().getName() + '@' + Integer.toHexString(hashCode())

如果调用obj.hashCode()，您将看到与toString相同的值.

If you call obj.hashCode() you'll see the same value that's shown by toString.

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