在java中将对象声明为final [英] Declaring object as final in java

问题描述

有人可以澄清以下代码的重要性。

Can someone clarify the significance of the below code.

class A
{
    int i = 10;

    public void setI(int b)
    {
        i = b;
    }

    public int getI()
    {
        return i;
    }
}

class Test
{    
    public static void main(String args[]) throws Throwable
    { 
        final A ob = new A();
        ob.setI(10);
        System.out.println(ob.getI());
    }
}

对象A被声明为final，但我可以更改此对象的实例变量的值，并还检索更新的值。那么将对象声明为final是什么意义。
我知道将原始数据类型声明为final，这使得该变量保持不变。

The object A is declared as final, but I can change value of this object's instance variable and also retrive the updated value. So what are the significance of declaring an object as final. I am aware about declaring primitive datatype as final, which makes that variable constant.

推荐答案

ob将无法引用任何其他对象：最终关键字。

ob will not be able to reference any other object : final keyword.

无法重新分配。但你可以改变它的内部（它是可变的，如果它是最初的）。
所以这样做：

It can not be reassigned. But you can change its internals (it is mutable, if it was originally). So this works :

  final A ob = new A();
  ob.setI(6)

但这不是：

  final A ob = new A();
  ob = new A();

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