了解 drawLine 的工作原理 [英] Understanding how drawLine works

问题描述

给定以下代码:

import javax.swing.*;
import java.awt.*;

public class NewClass extends JPanel {
    public void paintComponent(Graphics g) {
        g.drawLine(0, 0, 90, 90);
    }

    public static void main(String[] args) {
        JFrame jf = new JFrame();
        jf.add(new NewClass());
        jf.setSize(500, 500);
        jf.setVisible(true);
    }
}

如果方法 drawLine 是抽象的，为什么它会画一条线，正如我设法理解的那样，抽象方法没有定义?

Why does it draw a line if the method drawLine is abstract and, as I managed to understand, an abstract method has no definition?

先谢谢你！

推荐答案

paintComponent() 得到一个非抽象的 Graphics 子类，它实现了 drawLine().它必须得到一个非抽象的子类，因为抽象类不能被实例化.

paintComponent() gets a non-abstract sub-class of Graphics, which implements drawLine(). It must get a non-abstract sub-class, since an abstract class cannot be instantiated.

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