有人可以解释这是如何工作的吗? [英] can somebody explain how this works?

问题描述

我有这行代码.

class ButtonPanel extends JPanel implements ActionListener
{  
    public ButtonPanel()
    {  
        yellowButton = new JButton("Yellow");

它有效，我认为Java在创建这样的jButton实例之前需要知道yellowButton的类型?

and It works, I thought Java needs to know the type of yellowButton before creating an instance of a jButton like this?

JButton yellowButton = new JButton("Yellow");

有人可以解释一下这是如何工作的吗?

can somebody explain how this works?

推荐答案

如果它真的有效，那么这意味着 yellowButton 可能是一个你没有注意到的类字段.

If it really does work, then that means yellowButton is probably a class field that you didn't notice.

再次检查课程.您可能拥有的更像是这样的:

Check the class again. What you probably have is something more like this:

class ButtonPanel extends JPanel implements ActionListener
{  
    private JButton yellowButton;

    public ButtonPanel()
    {  
        yellowButton = new JButton("Yellow");
        /* this.yellowButton == yellowButton */

        /* etc */
    }
}

如果在方法作用域中找不到变量 foo，它会自动回退到 this.foo.相比之下，像 PHP 这样的一些语言没有这种灵活性.(对于 PHP，您总是必须执行 $this->foo 而不是 $foo 来访问类字段.)

If a variable foo cannot be found in a method scope, it automatically falls back to this.foo. In contrast, some languages like PHP do not have this flexibility. (For PHP you always have to do $this->foo instead of $foo to access class fields.)

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