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问题描述

Java中的所有原始包装类都是不可变对象吗?字符串是不可变的。什么是其他不可变对象?

Are all primitive wrapper classes in Java immutable objects? String is immutable. What are the other immutable objects?

推荐答案

任何不能为您提供更改数据的方法都是不可变的- 就这么简单。是的,所有原始包装类型都是不可变的,就像 String 一样。 ,和是其他示例。

Any type which doesn't give you any means to change the data within it is immutable - it's as simple as that. Yes, all the primitive wrapper types are immutable, as is String. UUID, URL and URI are other examples.

虽然内置Java API中的 Calendar Date 是可变的, 中的许多类型都是不可变的 - 在我看来,这是一个为什么Joda Time更容易使用。如果一个对象是不可变的,你可以在代码中的其他地方保留对它的引用,而不必担心其他一些代码是否会进行更改 - reason 更容易你的代码。

Although Calendar and Date in the built-in Java API are mutable, many of the types within Joda Time are immutable - and to my mind, this is one reason why Joda Time is easier to work with. If an object is immutable, you can keep a reference to it somewhere else in your code and not have to worry about whether or not some other piece of code is going to make changes - it's easier to reason about your code.

我的意思是 java.lang .Integer 等如其他地方所述, Atomic * 类是可变的,实际上是为了达到他们的目的。在标准的原始包装类集和包装原始值的类集之间我的想法有所不同。

by which I mean java.lang.Integer etc. As noted elsewhere, the Atomic* classes are mutable, and indeed have to be in order to serve their purpose. There's a difference in my mind between "the standard set of primitive wrapper classes" and "the set of classes which wrap primitive values".

你可以编写自己的可变包装器很容易上课:

You can write your own mutable wrapper class very easily:

public class MutableInteger
{
    private int value;

    public MutableInteger(int value) 
    {
         this.value = value;
    }

    public int getValue()
    {
        return value;
    }

    public void setValue(int value)
    {
        this.value = value;
    }
}

所以你可以看到,没有什么本质上不可变的包装类 - 只是标准的设计是不可变的,因为没有提供任何改变包装值的方法。

So as you can see, there's nothing inherently immutable about wrapper classes - it's just that the standard ones were designed to be immutable, by virtue of not providing any way to change the wrapped value.

请注意,这允许在装箱时重复使用相同的对象,对于常见值:

Note that this allows for the same object to be used repeatedly when boxing, for common values:

Integer x = 100;
Integer y = 100;
// x and y are actually guaranteed to refer to the same object

Integer a = 1000;
Integer b = 1000;
// a and b *could* refer to the same object, but probably won't

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10-18 22:39