问题描述

java GUI 的一个问题

初学者，在写一个GUI , 设置了几个按钮和对应的几个ActiveListener，监听器(MyFrame内部类)，MyFrame设置了一个成员变量flag，初值为0，重写了监听器方法，希望改变flag的值，但是在MyFrame中测试，flag一直为初值0，纠结很久了 万分感谢

解决方案

贴个完整带码看看看看看。

解决方案二：

import java.awt.*;
import java.awt.event.*;
import java.io.*;

public class Test {
public static void main(String[] args) {
new MyFrame("my java");

}

}

class MyFrame extends Frame {

int flag = 0;
MyFrame(String s) {
    super(s);
    setBounds(200,300,700,400);
    setLayout(new BorderLayout());

    Panel p1 = new Panel(new GridLayout());
    Panel p2 = new Panel(new BorderLayout());
    Panel p3 = new Panel(new FlowLayout());

  Button b1 = new Button("堆栈");
  b1.addActionListener(new MonitorSelect1(this));
  System.out.println(flag);
    Button b2 = new Button("队列");
    b2.addActionListener(new MonitorSelect2(this));
    Button b3 = new Button("串");
    b3.addActionListener(new MonitorSelect3(this));
  Button b4 = new Button("递归");
  b4.addActionListener(new MonitorSelect4(this));
    Button b5 = new Button("树");
    b5.addActionListener(new MonitorSelect5(this));

    BufferedReader br = null;
    String str = null;
    TextArea ta = new TextArea();
    Label l1 = new Label("代码区");
    Label l2 = new Label("功能区");
    Label ru = new Label("入队数据");
    TextField num1 = new TextField(10);
    Button sure = new Button("确定");
    Label chu = new Label("出队数据");
    TextField num2 = new TextField(10);

    p1.add(b1);
    p1.add(b2);
    p1.add(b3);
    p1.add(b4);
    p1.add(b5);
    add(p1,BorderLayout.NORTH);
    p2.add(l1,BorderLayout.NORTH);
    p2.add(ta,BorderLayout.CENTER);
    p2.add(l2,BorderLayout.SOUTH);
    add(p2,BorderLayout.CENTER);
    p3.add(ru);
    p3.add(num1);
    p3.add(sure);
    p3.add(chu);
    p3.add(num2);
    add(p3,BorderLayout.SOUTH);

    /*try {
         br = new BufferedReader(new FileReader("F:/java/TestBuffered/TestBuffered1.txt"));
         while((str = br.readLine()) != null)   {
            ta.append(str+"
");
         }
    }
    catch (IOException e) {
        System.out.println("文件读取错误");
    }*/

    pack();
    setVisible(true);
}

class MonitorSelect1 implements ActionListener {
    MyFrame mf = null;
    MonitorSelect1(MyFrame mf) {
        this.mf = mf;
    }
    public void actionPerformed(ActionEvent e) {
        mf.flag = 1;
    }
}

class MonitorSelect2 implements ActionListener {
    MyFrame mf = null;
    MonitorSelect2(MyFrame mf) {
        this.mf = mf;
    }
    public void actionPerformed(ActionEvent e) {
        mf.flag = 2;
    }
}

class MonitorSelect3 implements ActionListener {
    MyFrame mf = null;
    MonitorSelect3(MyFrame mf) {
        this.mf = mf;
    }
    public void actionPerformed(ActionEvent e) {
        mf.flag = 3;
    }
}

class MonitorSelect4 implements ActionListener {
    MyFrame mf = null;
    MonitorSelect4(MyFrame mf) {
        this.mf = mf;
    }
    public void actionPerformed(ActionEvent e) {
        mf.flag = 4;
    }
}

class MonitorSelect5 implements ActionListener {
    MyFrame mf = null;
    MonitorSelect5(MyFrame mf) {
        this.mf = mf;
    }
    public void actionPerformed(ActionEvent e) {
        mf.flag = 5;
    }
}

}

解决方案三：

Java序列化的一个问题

解决方案四：

public class Test1 {
public static void main(String[] args) {
new MyFrame("my java");

}

}

class MyFrame extends Frame {
int flag = 0;
MyFrame(String s) {
super(s);
Button b = new Button();
b.addActionListener(new Monitor(this));
System.out.println(flag);
}

class Monitor implements ActionListener {
        MyFrame mf = null;
        Monitor(MyFrame mf) {
            this.mf = mf;
        }
        public void actionPerformed(ActionEvent e) {
            mf.flag = 3;
        }
    }
}

大概就是这样的

解决方案五：

代码里的System.out.println(flag);是在监听器触发之前输出的，应该在监听器里面写System.out.println(flag);

解决方案六：

flag，应该改成静态的，我之前也遇到过这样的问题。

解决方案七：

flag改成静态的就行~