为什么我必须使用“ this”关键字以供参考？ [英] Why must I use the "this" keyword for forward references?

问题描述

当我使用 this 关键字访问类中的非静态变量时，Java不会给出任何错误。但是当我不使用它时，Java会报错。为什么我必须使用 this ？

When I use the this keyword for accessing a non-static variable in a class, Java doesn't give any error. But when I don't use it, Java gives an error. Why must I use this?

我知道什么时候通常应该使用 this ，但此示例与正常用法有很大不同。

I know when should normally I use this, but this example is very different from normal usages.

示例：

class Foo {
//  int a = b; // gives error. why ?
    int a = this.b; // no error. why ?
    int b;
    int c = b;

    int var1 = this.var2; // very interesting
    int var2 = this.var1; // very interesting
}

推荐答案

变量是首先声明，然后分配。该类与此相同：

Variables are declared first and then assigned. That class is the same as this:

class Foo {
    int a;
    int b;
    int c = b;

    int var1;
    int var2;

    public Foo() {
        a = b;

        var1 = var2;
        var2 = var1;
    }
}

不能执行的原因 int a = b; 是因为在创建对象时尚未定义 b ，而是对象本身（即这个）及其所有成员变量都存在。

The reason you can't do int a = b; is because b is not yet defined at the time the object is created, but the object itself (i.e. this) exists with all of its member variables.

下面是每个描述：

    int a = b; // Error: b has not been defined yet
    int a = this.b; // No error: 'this' has been defined ('this' is always defined in a class)
    int b; 
    int c = b;  // No error: b has been defined on the line before  

这篇关于为什么我必须使用“ this”关键字以供参考？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！