Java 代码 - 为什么要在此处克隆变量？

发布于 2024-10-01 14:58:36 字数 361 浏览 7 评论 0原文

看一下我从javax.naming.InitialContext复制的以下代码。 HashTable 类型的参数被传递给构造函数。这是代码片段

public InitialContext(Hashtable<?,?> environment) throws NamingException
{
    if (environment != null) {
        environment = (Hashtable)environment.clone();
    }
    init(environment);
}

我的问题是，为什么环境可以直接传递给 init 方法而在这里被克隆？

原文

Look at the following code which i am copying from javax.naming.InitialContext. An argument of HashTable type is being passed to the constructor. here is the code snippet

public InitialContext(Hashtable<?,?> environment) throws NamingException
{
    if (environment != null) {
        environment = (Hashtable)environment.clone();
    }
    init(environment);
}

My question is, why environment is being cloned here when it could have been passed directly to init method?

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你如我软肋 2024-10-08 14:58:37

因为它可以从这个方法的外部改变？

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走野 2024-10-08 14:58:36

此代码保护自身免受外部调用者更改 HashTable 状态的影响。

通过对其进行克隆，它们可以确保对传入的哈希表所做的更改不会反映在表传入的方法/对象内部。

使用数组的一个简短示例：

//Outside code
int[] arr = new int[]{0, 1, 2, 3};

// method of class
public void init(int[] arr) {
    this.arr = arr; 
}

//meanwhile, in the external code
arr[0] = 42; // this change to the array will be reflected inside the object.

可以通过复制数组来避免该漏洞。对原始数组的更改不会显示在副本中。

This code is protecting itself from an external caller changing the state of the HashTable.

By making a clone of it, they ensure that changes made to the Hashtable that was passed in are not reflected inside of the method/object the table was passed into.

A short example using arrays:

//Outside code
int[] arr = new int[]{0, 1, 2, 3};

// method of class
public void init(int[] arr) {
    this.arr = arr; 
}

//meanwhile, in the external code
arr[0] = 42; // this change to the array will be reflected inside the object.

That vulnerability can be avoided by making a copy of the array. Changes to the original array will not show up in the copy.

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