利用Java怎么获取文本框中的内容

import java.io.*;
import javax.swing.*;
import java.awt.FlowLayout;
import java.awt.event.*;
public class WriterTo extends JFrame implements ActionListener{
	JButton b;JTextField t;
	public WriterTo(){
		super("文本框内容写入文件");
		JLabel l=new JLabel("请输入内容：");
		t=new JTextField(20);
		b=new JButton("写入");
		b.addActionListener(this);
		this.add(l);
		this.add(t);
		this.add(b);
		this.setLayout(new FlowLayout());
		this.pack();
		this.setVisible(true);
	}
 public void actionPerformed(ActionEvent e) {
	 if(e.getSource()==b){
		 if(t.getText().equals("")){
			 JOptionPane.showMessageDialog(null,"请输入内容~","错误",JOptionPane.ERROR_MESSAGE);
			 t.grabFocus();
		 }else{
			 write(t.getText());
			 JOptionPane.showMessageDialog(null,"写入成功","提示",JOptionPane.INFORMATION_MESSAGE);
		 }
	 }
 }
 	public void write(String line){
 		try{
 			File f=new File("C:\\Users\\Administrator\\Desktop\\java\\就是这里.txt");//向指定文本框内写入
 			FileWriter fw=new FileWriter(f);
 			fw.write(line);
 			fw.close();
 		}catch(Exception e){
 		}
 	}
 	public static void main(String[] args) {
 		new WriterTo();
 	}
}