Java Swing组件下拉菜单控件JComboBox用法示例

程序员文章站 2024-04-01 21:10:10

本文实例讲述了java swing组件下拉菜单控件jcombobox用法。分享给大家供大家参考，具体如下： jcombobox是swing中的下拉菜单控件。它永远只能选中...

本文实例讲述了java swing组件下拉菜单控件jcombobox用法。分享给大家供大家参考，具体如下：

jcombobox是swing中的下拉菜单控件。它永远只能选中一个项目，然而比单选按钮节省空间。如果使用seteditable设置为true则内部选项的文本可以编辑，因此这种组件被称为组合框。注意，对选项的编辑只会影响当前项，而不会改变列表内容。可以使用additem方法来添加选项列表，或者使用insertitemat在任何位置插入选项；然而如果有大量选项需要添加，这种方法是非常笨重的，可以先构造一个defaultcomboboxmodel，使用addelement加载选项，最后在调用jcombobox的setmodel方法。

常用方法如下：

Java Swing组件下拉菜单控件JComboBox用法示例

示例代码：

jcomboboxbasicusedemo.java

package awtdemo;
import java.awt.borderlayout;
import java.awt.font;
import java.awt.event.actionevent;
import java.awt.event.actionlistener;
import java.awt.event.itemevent;
import java.awt.event.itemlistener;
import javax.swing.jcombobox;
import javax.swing.jframe;
import javax.swing.jlabel;
import javax.swing.event.popupmenuevent;
import javax.swing.event.popupmenulistener;
/*
 * 演示jcombobox的基本用法，以及事件响应
 */
public class jcomboboxbasicusedemo extends jframe{
  private static final long serialversionuid = -8161981948004677531l;
  int default_width = 600;
  int default_height = 400;
  private jlabel label;
  private jcombobox<string> facecombo;
  private static final int fontsize = 12;  
  @suppresswarnings("unused")
    public jcomboboxbasicusedemo(){
    settitle("jcomboboxdemo - www.jb51.net");
    setsize(default_width, default_height);
    //添加label
    label = new jlabel("欢迎来到 www.jb51.net");
    label.setfont(new font("serif",font.plain, fontsize));
    add(label, borderlayout.center);
    //actionlistener
    actionlistener actionlistener = new actionlistener(){
      public void actionperformed(actionevent e) {
        if(e.getsource() instanceof jcombobox){
          @suppresswarnings({ "unchecked", "rawtypes" })
          jcombobox<string> combobox = (jcombobox)e.getsource();
          string fontname = combobox.getselecteditem().tostring();
          label.setfont(new font(fontname, font.plain, fontsize));
          system.out.printf("%s%n", "actionperformed called");
        }
      }
    };
    //popupmenulistener
    popupmenulistener popupmenulistener = new popupmenulistener() {
      @override
      public void popupmenucanceled(popupmenuevent e) {
        system.out.println("下拉菜单取消");
      }
      @suppresswarnings("unchecked")
            @override
      public void popupmenuwillbecomeinvisible(popupmenuevent e) {
        system.out.println("下拉菜单合上");
        jcombobox<string> source = (jcombobox<string>)e.getsource();
      }
      @override
      public void popupmenuwillbecomevisible(popupmenuevent e) {
        system.out.println("下拉菜单弹出");
      }
    };
    //itemlistener
    itemlistener itemlistener = new itemlistener() {
      @override
      public void itemstatechanged(itemevent arg0) {
        // todo auto-generated method stub
        if(itemevent.selected == arg0.getstatechange()){
          string selecteditem = arg0.getitem().tostring();
          label.setfont(new font(selecteditem, font.plain, fontsize));
          system.out.printf("new selected item : %s%n",selecteditem);
        }
        if(itemevent.deselected == arg0.getstatechange()){
          string selecteditem = arg0.getitem().tostring();
          system.out.printf("deselected item : %s%n",selecteditem);
        }
      }
      };
    //添加一个jcombobox
    facecombo = new jcombobox<string>();
    facecombo.seteditable(true);
    //facecombo.addactionlistener(actionlistener);
    //facecombo.addpopupmenulistener(popupmenulistener);
    facecombo.additemlistener(itemlistener);
    facecombo.setenabled(true);
    facecombo.additem("serif");
    facecombo.additem("sansserif");
    facecombo.additem("monospaced");
    facecombo.additem("dialog");
    facecombo.additem("dialoginput");
    add(facecombo, borderlayout.south);
  }
  public static void main(string[] args) {
    // todo auto-generated method stub
    //创建窗体并指定标题
    jcomboboxbasicusedemo frame = new jcomboboxbasicusedemo();
    //关闭窗体后退出程序
    frame.setdefaultcloseoperation(jframe.exit_on_close);
    //自动适配所有控件大小
    //frame.pack();
    //设置窗体位置在屏幕*
    frame.setlocationrelativeto(null);
    //显示窗体
    frame.setvisible(true);
  }
}

本程序的基本功能是，通过选择不同的item而相应地改变界面中的英文字体（如本例中的www.jb51.net）。运行效果如下：

Java Swing组件下拉菜单控件JComboBox用法示例