例子：

public class ButtonDemo extends JFrame {

private JButton leftbtn = new JButton(">=");

private JButton rightBtn = new JButton("<=");

//构造方法
public ButtonDemo (){
    //创建Panel
JPanel panel = new JPanel();
panel.add(new JLabel("welcome to Java"));

JPanel bottomPanel = new JPanel();
//当前模型上的键盘助记符
leftbtn.setMnemonic('L');
leftbtn.setToolTipText("Move message to left");

rightBtn.setMnemonic('R');
rightBtn.setToolTipText("move message to right ");
//添加到panel
bottomPanel.add(leftbtn);
bottomPanel.add(rightBtn);

//设置布局
BorderLayout layout = new BorderLayout();
setLayout(layout);
add(panel,layout.CENTER);
add(bottomPanel,layout.SOUTH);


//添加事件
    leftbtn.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            moveLeft();
        }
    });

    rightBtn.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            moveRight();
        }
    });



}

public void  moveLeft(){
    System.out.println("向左移动");
}

public void  moveRight(){
    System.out.println("向右移动");
}

public static void main(String[] args) {
    ButtonDemo frame = new ButtonDemo();
    //自动调整框架大小
    frame.pack();
    frame.setTitle("buttonDemo");
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
}
}

结果：

屏幕快照 2018-10-25 上午11.20.55.png

2、案例2、

屏幕快照 2018-10-25 下午4.31.25.png

public class DespritionPanel extends JPanel{

private JLabel disLable = new JLabel();
private JTextArea textArea = new JTextArea();

public DespritionPanel(){
   disLable.setForeground(Color.red);
    disLable.setHorizontalAlignment(JLabel.CENTER);
    disLable.setHorizontalTextPosition(JLabel.CENTER);
    disLable.setVerticalTextPosition(JLabel.BOTTOM);
    disLable.setFont(new Font("",Font.BOLD,22));

    //可以滚动的panel
    JScrollPane displayPanel = new JScrollPane(textArea);
   textArea.setFont(new Font("",Font.ITALIC,15));
    textArea.setLineWrap(true);//自动换行
    textArea.setWrapStyleWord(true);//按单词而不是字符
    textArea.setEditable(true);

    setLayout(new BorderLayout(5,5));
    add(disLable,BorderLayout.CENTER);
    add(displayPanel,BorderLayout.WEST);
}

  //设置数据
public void settitle(String title){
    disLable.setText(title);
}
 //设置数据
public void setImageIcon(ImageIcon icon){
    disLable.setIcon(icon);
}
  //设置数据
public void setdesp(String desp){
    textArea.setText(desp);
}
}

ComboBoxclass 实现

 public class ComboBoxclass extends JFrame {

//combobox 的标题
private String [] titleArr = {"china","canada","USA","England","Franch"};

//描述的数组
private String [] despArr = new String[titleArr.length];

//图片数组
private ImageIcon [] flagimgArr = {
        new ImageIcon("ImageSource/1.png"),
        new ImageIcon("ImageSource/1.png"),
        new ImageIcon("ImageSource/1.png"),
        new ImageIcon("ImageSource/1.png"),
        new ImageIcon("ImageSource/1.png"),
};

//下拉框
private JComboBox comboBox = new JComboBox(titleArr);

//
private DespritionPanel despPanel = new DespritionPanel();

public  ComboBoxclass(){

    despArr[0] = "xdgfhjklpoliuytrdfgyhujikopoiuygfdfghjkllknbvbnm,xdgfhjklpoliuytrdfgyhujikopoiuygfdfghjkllknbvbnm,xdgfhjklpoliuytrdfgyhujikopoiuygfdfghjkllknbvbnm,xdgfhjklpoliuytrdfgyhujikopoiuygfdfghjkllknbvbnm,xdgfhjklpoliuytrdfgyhujikxdgfhjklpoliuytrdfgyhujikopoiuygfdfghjkllknbvbnm,opoiuygfdfghjkllknbvbnm,./;lkiuygtf";
    despArr[1] = "qwwwwwwww";
    despArr[2] = "assszxcxc";
    despArr[3] = "yyy6666666";
    despArr[4] = "211223ddfggdss";

   add(comboBox, BorderLayout.NORTH);
    add(despPanel,BorderLayout.CENTER);

    comboBox.addItemListener(new ItemListener() {
        @Override
        public void itemStateChanged(ItemEvent e) {
            setdata(comboBox.getSelectedIndex());
        }
    });

   //设置默认数据
    setdata(0);
}

public static void main(String[] args) {
   ComboBoxclass frame = new ComboBoxclass();
    frame.setTitle("combox");
    frame.setSize(300,300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}

//设置数据
public void setdata(int index){
   despPanel.settitle(titleArr[index]);
    despPanel.setImageIcon(flagimgArr[index]);
    despPanel.setdesp(despArr[index]);
}
}