GUI矩形、椭圆、线、框架

所有的Swing组件必须由时间调度线程(event dispatch thread)进行配置，线程将鼠标点击和键盘敲击控制转移到用户接口组件。下面的代码片段是事件调度线程中的执行代码:

EventQueue.invokeLater(new Runnable(){

    public void run(){

        statements

    }

});

注释：主线程中完成Swing程序初始化无法保证这种方式的安全性，虽然发生错误的概率非常小。

根据屏幕分辨率重置框架的大小
调用Toolkit类的静态方法getDefaultToolkit得到一个Toolkit对象(Toolkit类包含很多与本地窗口系统打交道的方法)。然后，调用getScreenSize方法，这个方法以Dimension对象的形势返回屏幕的大小。Dimension对象同时用公有实例变量width和height保存着屏幕的宽度和高度。下面是相关代码：

    Toolkit kit = Toolkit.getDefaultToolkit();

    Dimension screenSize = kit.getScreenSize();

    int screenWidth = screenSize.width;

    int screenHeight = screenSize.height;

下面，将框架大小设定为上面取值的50%,然后告知窗口系统定位框架

    setSize(screenWidth/2,screenHeight/2);

    setLocationByPlatform(true);

绘制几何图形

import java.awt.EventQueue;

import javax.swing.JFrame;

public class DrawTest {

    public static void main(String[] args) {

        EventQueue.invokeLater(new Runnable() {

            public void run() {

                JFrame frame = new DrawFrame();

                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

                frame.setVisible(true);

            }

        });

    }

}

import java.awt.Component;

import java.awt.Dimension;

import java.awt.Toolkit;

import javax.swing.JFrame;

public class DrawFrame extends JFrame {

    public DrawFrame() {

        setTitle("DrawTest");

//      setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

        Toolkit toolkit = Toolkit.getDefaultToolkit();

        Dimension screenSize = toolkit.getScreenSize();

        int screenWidth =screenSize.width;

        int screenHeight = screenSize.height;

        setSize(screenWidth/2, screenHeight/2);

        setLocationByPlatform(true);

        component = new DrawComponent();

        add(component);

    }

    private Component component;

    public static final int DEFAULT_WIDTH = 400;

    public static final int DEFAULT_HEIGHT = 400;

}

import java.awt.Dimension;

import java.awt.Graphics;

import java.awt.Graphics2D;

import java.awt.Toolkit;

import java.awt.geom.Ellipse2D;

import java.awt.geom.Line2D;

import java.awt.geom.Rectangle2D;

import javax.swing.JComponent;

public class DrawComponent extends JComponent {

    public void paintComponent(Graphics g) {

        Graphics2D g2 = (Graphics2D) g;

        //根据屏幕分辨率设置框架大小

        Toolkit toolkit = Toolkit.getDefaultToolkit();

        Dimension screenSize = toolkit.getScreenSize();

        int screenWidth = screenSize.width;

        int screenHeight = screenSize.height;

        //根据屏幕分辨率设置组件位置

        double leftX = screenWidth / 4 - 100;

        double topY = screenHeight / 4 - 75;

        double width = 200;

        double height = 150;

        //画一个矩形

        Rectangle2D rec = new Rectangle2D.Double(leftX, topY, width, height);

        g2.draw(rec);

        //画一个rec矩形的内切椭圆

        Ellipse2D ellipse = new Ellipse2D.Double();

        ellipse.setFrame(rec);

        g2.draw(ellipse);

        //画rec矩形的对角线

        g2.draw(new Line2D.Double(leftX, topY, leftX + width, topY + height));

        //画一个以rec矩形中心为圆心的圆

        double centerX = rec.getCenterX();

        double centerY = rec.getCenterY();

        double radius = 150;

        Ellipse2D circle = new Ellipse2D.Double();

        circle.setFrameFromCenter(centerX, centerY, centerX + radius, centerY + radius);

        g2.draw(circle);

    }

}

以上内容根据《java核心技术卷I：基础知识》编写