关于GUI中空指针异常的问题 - 黑马程序员技术交流社区

import java.awt.*;
import java.awt.event.*;
import java.io.*;
class MyWindowDemo
{
private Frame f;
private TextField tf;
private Button but;
private TextArea ta;
private Dialog d;
private Label lab;
private Button lbut;
MyWindowDemo()
{
init();
}
public void init()
{
f = new Frame("my window");
f.setBounds(300,100,500,400);
f.setLayout(new FlowLayout());
tf = new TextField(30);
but = new Button("提交");
ta = new TextArea(15,40);
f.add(tf);
f.add(but);
f.add(ta);
myEvent();
f.setVisible(true);
}
public void myEvent()
{
but.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
ta.setText("");
String dirPath = tf.getText();
File dir = new File(dirPath);
if(dir.exists() && dir.isDirectory())
{
String[] names = dir.list();
for(String name :names)
{
ta.append(name+"\r\n");
//sop(name);
}
} else
{
sop("sdas");
d = new Dialog(f,"lallalalalal",true);
lab = new Label("-------fail--------");
lbut = new Button("ok");
d.setBounds(400,200,500,100);
d.setLayout(new FlowLayout());
d.add(lab);
d.add(lbut);
d.setVisible(true);
}
}
});
f.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
});
ta.addKeyListener(new KeyAdapter()
{
public void keyPressed(KeyEvent e)
{
e.consume();
}
});
/* 从这里往下再运行时,具体说是初始化的时候就已经报空指针异常
d.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
d.setVisible(false);
}
});
lbut.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
d.setVisible(false);
}
});
*/
}
public static void main(String[] args)
{
new MyWindowDemo();
}
public static void sop(Object obj)
{
System.out.println(obj);
}
}

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