现场直憋啊！

Question

package day11;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class ItemTest {
private JFrame jf;
private JComboBox box1,box2;
private JLabel label1,label2;
private Object[] obj1;//省份
private Object[][] obj2;//城市

public ItemTest(Object[] obj1,Object[][] obj2){
this.obj1=obj1;
this.obj2=obj2;
jf=new JFrame("Item Event Test");
box1=new JComboBox(obj1);
box2=new JComboBox(obj2[0]);
label1=new JLabel("省份:");
label2=new JLabel("城市:");
jf.setLayout(new FlowLayout());
jf.add(label1);
jf.add(box1);
jf.add(label2);
jf.add(box2);
addEventHandler();
}

public void addEventHandler(){
box1.addItemListener(new ItemListener(){
                public void itemStateChanged(ItemEvent arg0) {
int index= box1.getSelectedIndex();
box2.removeAllItems();

for(int i=0;i<obj2[index].length;i++){
box2.addItem(obj2[index][i]);
}

}

});
}

public void showMe(){
jf.setSize(400,300);
jf.setVisible(true);
jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args){
Object[] obj1=new Object[]{"河北","河南","江苏","山东","辽宁"};
Object[][] obj2=new Object[][]{
{"石家庄","保定","廊坊","邯郸","秦皇岛"},
{"郑州","许昌","洛阳","南阳","开封","驻马店"},
{"济南","青岛","烟台","威海","泰安","潍坊"},
{"南京","苏州","徐州","扬州","无锡"},
{"沈阳","大连","锦州","铁岭","辽阳","丹东"}
};
new ItemTest(obj1,obj2).showMe();
}}
构造方法中box2=new JComboBox(obj2[0]);把box2初始化了
我把addEventHandler方法中for(int i=0;i<obj2[index].length;i++){
box2.addItem(obj2[index][i]);
}
换成box2=new JComboBox(obj2[index]);为啥就不好使了呢？？
憋死我这个新手了！求解！

Answer 1

index有值吗 应该是一个正整数才行啊

Answer 2

int index= box1.getSelectedIndex(); 
index有值的呀

Answer 3

public void addEventHandler() {
box1.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent arg0) {
int index = box1.getSelectedIndex();
ItemTest.this.jf.doLayout();
ItemTest.this.jf.remove(box2);
ItemTest.this.jf.repaint();

box2 = new JComboBox(obj2[index]);
ItemTest.this.jf.add(box2);
ItemTest.this.jf.doLayout();
ItemTest.this.jf.validate();
} });
}

Answer 4

ItemTest.this.jf.doLayout();
这句可能可以去掉的。
你的布局做的不好，应该固定combox的宽度。现在这样，位置一直不固定。

Answer 5

谢谢！能给我讲解一下为什么我把addEventHandler方法中for(int i=0;i <obj2[index].length;i++){ 
box2.addItem(obj2[index][i]); 
} 
换成box2=new JComboBox(obj2[index]);就不行吗？

Answer 6

可能跟java的垃圾回收一样。box2正在使用中，所以不能赋值。