JAVA入门系列四

窗体程序
在组件中显示信息
例：

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

public class TXTDisplay {

	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable()
				{
			public void run()
			{
				TXTDisplayFrame frame = new TXTDisplayFrame();
				frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				frame.setVisible(true);
			}
				});
		
	}

}

class TXTDisplayFrame extends JFrame
{
	public TXTDisplayFrame()
	{
		setTitle("窗口");
		setSize(a,b);
		
		TXTDisplayPanel panel = new TXTDisplayPanel();
		add(panel);
	}
	public static final int a=200;
	public static final int b=200;
}

class TXTDisplayPanel extends JPanel
{
	public void paintComponent(Graphics g)
	{
		g.drawString("文本部分",start,end);
	}
	public static final int start = 75;
	public static final int end = 100;
}

注：
1.paintComponent方法有一个Graphics类型的参数，这个参数保存着用于绘制图像和文本的设置；在Java中，所有的绘制都必须使用Graphics对象，其中包含了绘制图像和文本的方法。
2.container getContentPane() 返回这个JFrame的内容窗格对象。
3.Component add(Component c) 将一个给定的组件添加到该框架的内容窗格中。

2D图形
Graphics类包含绘制直线，椭圆和矩形等方法。要想使用Java 2D库绘制图形，需要获得Graphics 2D类对象；paintComponent方法会自动获得一个Graphics2D类对象，需要进行一次类型转换：
public void paintComponent(Graphics g)
{
Graphics2D g2 = (Graphics2D) g;
…
}

简单的绘制图形例子：

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

public class DrawTest {

	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable()
				{
			public void run()
			{
				DrawFrame frame = new DrawFrame();
				frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				frame.setVisible(true);
			}
				});
	}

}

class DrawFrame extends JFrame
{
	public DrawFrame()
	{
		setTitle("DrawTest");
		setSize(DEFAULT_WIDTH,DEFAULT_HEIGHT);
		DrawComponent component = new DrawComponent();
		add(component);
	}
	public static final int DEFAULT_WIDTH = 300;
	public static final int DEFAULT_HEIGHT = 200;
}

class DrawComponent extends JComponent
{
	public void paintComponent(Graphics g)
	{
		Graphics2D g2 = (Graphics2D) g;
		double leftX=290;
		double topY=190;
		double width=280;
		double height=180;
		
		Rectangle2D rect = new Rectangle2D.Double(leftX, topY, width, height);
		g2.draw(rect);
		
		Ellipse2D ellipse = new Ellipse2D.Double();
		ellipse.setFrame(rect);
		g2.draw(ellipse);
		g2.draw(new Line2D.Double(leftX, topY, width, height));
		
		double centerX=rect.getCenterX();
		double centerY=rect.getCenterY();
		double radius = 150;
		
		Ellipse2D circle = new Ellipse2D.Double();
		circle.setFrameFromCenter(centerX,centerY,centerX+radius,centerY+radius);	
	}
}