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