- 单选按钮
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JRadioButton radioButton1 = new JRadioButton("Java");// 创建单选按钮 contentPane.add(radioButton1);// 应用单选按钮 ? JRadioButton radioButton2 = new JRadioButton("PHP");// 创建单选按钮 contentPane.add(radioButton2);// 应用单选按钮 ? JRadioButton radioButton3 = new JRadioButton("C++");// 创建单选按钮 contentPane.add(radioButton3);// 应用单选按钮 ? ButtonGroup group = new ButtonGroup();// 创建单选按钮组 group.add(radioButton1);// 将radioButton1增加到单选按钮组中 group.add(radioButton2);// 将radioButton2增加到单选按钮组中 group.add(radioButton3);// 将radioButton |
- 嵌套窗体
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package com.pcx.test; import java.awt.*; import java.awt.event.*; import javax.swing.*; ? public class TestInternalFrame { ????final int DESKTOP_WIDTH = 480; ????final int DESKTOP_HEIGHT = 360; ????final int FRAME_DISTANCE = 30; ? ????JFrame jf = new JFrame("父窗口"); ????// 定义一个虚拟桌面 ????private JDesktopPane desktop = new JDesktopPane(); ????// 保存下一个内部窗口的座标点 ????private int nextFrameX; ????private int nextFrameY; ????// 定义内部窗口为虚拟桌面的1/2大小 ????private int width = DESKTOP_WIDTH / 2; ????private int height = DESKTOP_HEIGHT / 2; ????// 为主窗口定义2个菜单 ????JMenu fileMenu = new JMenu("文件"); ????// 定义newAction用于创建菜单和工具按钮 ????Action newAction = new AbstractAction("新建", new ImageIcon("ico/new.png")) { ????????public void actionPerformed(ActionEvent event) { ????????????// 创建内部窗口 ????????????final JInternalFrame iframe = new JInternalFrame("新文档", true, // 可改变大小 ????????????????????true, // 可关闭 ????????????????????true, // 可最大化 ????????????????????true); // 可最小化 ????????????iframe.add(new JScrollPane(new JTextArea(8, 40))); ????????????// 将内部窗口添加到虚拟桌面中 ????????????desktop.add(iframe); ????????????// 设置内部窗口的原始位置（内部窗口默认大小是0X0，放在0,0位置） ????????????iframe.reshape(nextFrameX, nextFrameY, width, height); ????????????// 使该窗口可见，并尝试选中它 ????????????iframe.show(); ????????????// 计算下一个内部窗口的位置 ????????????nextFrameX += FRAME_DISTANCE; ????????????nextFrameY += FRAME_DISTANCE; ????????????if (nextFrameX + width > desktop.getWidth()) ????????????????nextFrameX = 0; ????????????if (nextFrameY + height > desktop.getHeight()) ????????????????nextFrameY = 0; ????????} ????}; ????// 定义exitAction用于创建菜单和工具按钮 ????Action exitAction = new AbstractAction("退出", new ImageIcon("ico/exit.png")) { ????????public void actionPerformed(ActionEvent event) { ????????????System.exit(0); ????????} ????}; ? ????public void init() { ????????// 为窗口安装菜单条和工具条 ????????JMenuBar menuBar = new JMenuBar(); ????????JToolBar toolBar = new JToolBar(); ????????jf.setJMenuBar(menuBar); ????????menuBar.add(fileMenu); ????????fileMenu.add(newAction); ????????fileMenu.add(exitAction); ????????toolBar.add(newAction); ????????toolBar.add(exitAction); ????????desktop.setPreferredSize(new Dimension(480, 360)); ????????// 将虚拟桌面添加到顶级JFrame容器中 ????????jf.add(desktop); ????????jf.add(toolBar, BorderLayout.NORTH); ????????jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); ????????jf.pack(); ????????jf.setVisible(true); ????} ? ????public static void main(String[] args) { ????????new TestInternalFrame().init(); ????} } |
- 设置标签中的字体
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int size=14; label.setFont(new Font("Serif",Font.PLAIN,size)); |
- 如何在jlabel中设置文本的换行
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String info="<html>你的ID号是："+user.getId()+"<br/>"+"你的用户名是："+user.getName()+"</html>"; Label.settext(info); |
- 类型转换异常
public class Test {
?public static void main(String[] args){
??Animal cat=new Cat();
??Animal dog=new Dog();
??Object b=new Animal();
??Object d=new Cat();
??displayObject(cat);
??displayObject(dog);
????// Cat c=(Cat)b; //Animal cannot be cast to Cat
???// Cat cc=d;//cannot convert from Object to Cat
?????Cat ee=(Cat)d;
?cat.output();//if the method output() is undefined in class Cat,then the output would be "I am an animal"
?// a.speak(); //the method speak() is undefined for the type Animal
?}
??public static void??displayObject(Object obj){
???if(obj instanceof Cat)
????((Cat) obj).speak();
???else if(obj instanceof Dog)
????((Dog)obj).speak();
??}
}
class Animal{
?void?output(){
??System.out.println("I am an animal");
?}?
}
?class Cat extends Animal{
??void speak(){
???System.out.println("喵喵~");
??}
?void?output(){
???System.out.println("I am a cat");
??}
??
?}
?
?class Dog extends Animal{
??void speak(){
???System.out.println("汪汪~");
??}
?void?output(){
???System.out.println("I am a dog");
???}
?}通过该程序，我有如下理解：
1.父类对象可以强制转换为子类对象，但是前提是此父类对象为子类对象实例化的结果。
e.g. Fruit fruit=new Apple();
?????Apple a=(Apple)fruit;//ok
e.g. 假设Apple类继承于Fruit类，
?????Object fruit=new Fruit();
?????Object apple=(Apple)fruit;//wrong
2.子类的实例向父类转型是为了实现多态。
?
? - 图片文本最佳的封装方案
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background2 = new JLabel(new ImageIcon( ????????????????MainUI.class.getResource("/com/nt/image/main.gif"))); ????????Random rd = new Random(); ????????stream = MainUI.class.getResourceAsStream("/com/nt/file/" ????????????????+ rd.nextInt(19) + ".txt"); ????????try { ????????????read = new BufferedReader(new InputStreamReader(stream, "GBK")); |
- 在panel里面设置背景图片
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