Java interface programming method to build a simple framework that can draw graphics

This article introduces the method of Java interface programming to build a simple framework that can draw graphics

Introduction: Use a total of 3.java files to build a simple interface programming framework.

The first file: NotHelloWorldComponent.java

//NotHelloWorldComponent.java
import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;

public class NotHelloWorldComponent extends JComponent {
    public static final int MESSAGE_X = 75;　　//消息最左上角坐标
    public static final int MESSAGE_Y = 75;
    
　　　　//定义此界面的默认尺寸
    private static final int DEFAULT_WIDTH = 300;　　
    private static final int DEFAULT_HEIGHT = 300;
    
　　　　//paintComponent()会被系统自动调用，并且系统会自动传递一个Graphics对象给它
    public void paintComponent(Graphics g){
        //将g转型成Graphics2D对象，作为画笔，用来画2D图形
        Graphics2D g2 = (Graphics2D)g;
        
　　　　　　//创建一个Rectangle2D矩形对象
　　　　　　//如果有其他图形需要绘制，可以先在此处定义，再在下个部分用g2作为画笔画出来
        double leftX = 50;
        double topY = 50;
        double width = 200;
        double height = 150;
        Rectangle2D rect = new Rectangle2D.Double(leftX, topY, width, height);
        
　　　　　　//用画笔g2来绘制文字和矩形图形
        g2.drawString("Not a hello, World program", MESSAGE_X, MESSAGE_Y);　　
        g2.draw(rect);
        
    }
    
　　　　//覆盖此函数，设置首选的尺寸大小
    @Override
    public Dimension getPreferredSize() {
        return new Dimension(DEFAULT_WIDTH, DEFAULT_HEIGHT);
    }
}

The second .java file: NotHelloWorldFrame.java

import javax.swing.JFrame;

public class NotHelloWorldFrame extends JFrame {
    public NotHelloWorldFrame(){
        add(new NotHelloWorldComponent());
        pack();    //使JFrame的大小适合其包含的组件的大小
    }
}

Description: JFrame is a frame class used to contain JPanel and JComponent.

The third .java file: NotHelloWorld.java

import java.awt.EventQueue;

import javax.swing.JFrame;

public class NotHelloWorld {
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {　　//使用匿名内部类技术，创建一个线程，用线程来创建窗口程序
            public void run() {
                JFrame frame = new NotHelloWorldFrame();
                frame.setTitle("NotHelloWorldFrame");　　　　
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);　　//关闭窗口的同时，程序结束，避免内存垃圾
                frame.setVisible(true);　　　　//开启窗口可见
            }
        });
    }
}

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