java JMenuBar不可见?为什么? [英] java JMenuBar not visible? Why?
问题描述
我无法弄清楚为什么菜单栏不可见.我有以下代码:
I cannot figure out why my menu bar isn't visible. I have following code:
//主
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class Menu extends JFrame{
public static void main(String[] args){
JFrame frame = new JFrame();
frame.setSize(500,350);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
menuBar mbObj = new menuBar();
mbObj.menuBar(frame);
}
}
//菜单栏类
public class menuBar{
private JMenu file,edit;
private JMenuItem nFile ,oFile,sFile,saFile,exit;
private JMenuItem undo,copy,paste;
private JMenuBar bar;
public void menuBar(JFrame frame){
bar = new JMenuBar();
frame.setJMenuBar(bar);
bar.setVisible(true);
file = new JMenu("File");
edit = new JMenu("Edit");
bar.add(file);
bar.add(edit);
}
}
推荐答案
在顶级窗口(这里是JFrame)上调用setVisible(true)
,仅在之后添加所有组件,包括JMenuBar
.您还希望避免在任何情况下调用setSize(...)
,而是在添加所有组件之后且在调用setVisible(true)
之前,使用布局管理器并在JFrame上调用pack()
.
Call setVisible(true)
on the top-level window, here a JFrame, only after adding all components, including the JMenuBar
. You will also want to avoid calling setSize(...)
on anything, and instead use layout managers and call pack()
on the JFrame after adding all components and before calling setVisible(true)
.
因此顺序应为:
// create JFrame
JFrame frame = new JFrame("Foo");
// here add all components to the JFrame
// .....
// done adding components
frame.pack();
// frame.setLocationRelativeToPlatform(true); // if you wish
frame.setVisible(true);
顺便说一句,类的名称应以大写字母开头,并且不具有与该类名称完全相同的方法,因为这会创建伪"构造函数,并使所有人感到困惑.
As an aside class names should begin with an upper case letter, and dont have methods with the exact same name as the class, as that creates a "pseudo"-constructor and will confuse everyone.
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