第二次作业

JComboBox的使用方法：

JComboBox是swing种的下拉菜单控件。最常使用的函数应该是addItem()方法，可以为该控件添加一个个下拉选项。

然后要处理选中某个选项的事件，可以添加ItemListener监听器。

[java] view plain copy

comboBox1.addItemListener(new java.awt.event.ItemListener(){

public void itemStateChanged(java.awt.event.ItemEvent e){

func(e);//处理事件的函数

}

});

但是有可能会对一个选择事件处理两次。假设func(e)函数中输出a，则在一次选择后，会发现输出了aa，这是因为itemStateChanged()函数与itemState有关，而itemState状态有两个：Selected和Unselected。即在一次选择的过程中，实际出发了两个事件，unselect上一次选中的事件，select本次选中的事件。

import java.awt.BorderLayout;

import java.awt.Container;

import java.awt.Dimension;

import java.awt.FlowLayout;

import java.awt.GridLayout;

import java.awt.Toolkit;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.JButton;

import javax.swing.JComboBox;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JOptionPane;

import javax.swing.JPanel;

import javax.swing.JTextField;

public class log {

public JFrame frame;

private JTextField log_text;

private JTextField name_text;

public log() {

makeframe();

}

public void makeframe(){

frame =new JFrame("登录程序");

Container contentpane=frame.getContentPane();

JPanel northPanel = new JPanel(new GridLayout(7, 1));
JPanel north1=new JPanel(new FlowLayout());

JPanel north2=new JPanel(new FlowLayout());
JPanel north3=new JPanel(new FlowLayout());
JTextField Name_text = new JTextField(16);
JTextField Log_text = new JTextField(16);
JLabel Name=new JLabel("用户名");
//  contentpane.add(Name,BorderLayout.NORTH);
JLabel  Log=new JLabel("登录 密码");
north1.add(Name);
north2.add(Log);
north1.add(Name_text);
north2.add(Log_text);
JButton yes=new JButton("确定");
JButton no=new JButton("取消");
north3.add(yes);
north3.add(no);
//contentpane.add(Log,BorderLayout.SOUTH);
contentpane.add(northPanel);
northPanel.add(north1);
northPanel.add(north2);
northPanel.add(north3);

String[] list={"尹鑫磊","S卞","B琛"};
JComboBox ComboBox=new JComboBox(list);
ComboBox.addActionListener(new ActionListener(){

public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
JComboBox ComboBox = (JComboBox)e.getSource();
String petName = (String)ComboBox.getSelectedItem();
String petName1 = (String)ComboBox.getToolTipText();
updateLabel(petName);
System.out.println(petName);
System.out.println(petName1);
}
public void updateLabel(String petName) {
// TODO Auto-generated method stub
}});
yes.addActionListener(new ActionListener(){

public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
JOptionPane.showMessageDialog(frame, "正确", "登陆成功", JOptionPane.INFORMATION_MESSAGE);

}});
no.addActionListener(new ActionListener(){

public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
System.exit(0);
}});

north1.add(ComboBox);

frame.setVisible(true);
Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
frame.setLocation(d.width/2 - frame.getWidth()/2, d.height/2 -
frame.getHeight()/2);
frame.pack();

}

/**

* @param args

*/

public static void main(String[] args) {

// TODO Auto-generated method stub

new log();

}

}