TextArea没有响应

Question

我在单击按钮时尝试在TextArea中设置文本，但没有显示任何文本。我该怎么办？

我想从文本字段中找到该数字的所有素数，但textarea没有响应？

package primnum;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.ScrollPane;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

public class Pframe extends JFrame {
private JLabel l1,l2, l3;
private JTextField f1 ;
private JButton b;
private JTextArea t;
private JPanel p ,p1,p2;
private String s, s2, s3;
private int m ;
private Font f;

public Pframe(){
        super("Prime Numbers");
        //setLayout(new GridLayout(3,1));
        s = new String("Enter a Number (N)");
        f = new Font("SanSarif" , Font.BOLD,14);
        l1 = new JLabel(s);
        l3=new JLabel("           ");
        l1.setFont(f);
        p = new JPanel();
        p.setLayout(new FlowLayout());
        p.add(l1);
        f1 = new JTextField(20);
        p.add(f1);
        add(p,BorderLayout.NORTH);
        p1 = new JPanel();
        p1.setLayout(new GridLayout(4,1));
        b = new JButton("Find Primes");
        b.setSize(1, 3);
        p1.add(l3);
        p1.add(b);
        add(p1,BorderLayout.CENTER);
        l2 = new JLabel("           List Of Prime Numbers Less than N");
        l2.setFont(f);
        p2 =new JPanel();
        t = new JTextArea(null,20,60);
        t.setEditable(false);
        p2.add(l2,BorderLayout.NORTH);
        p2.add(new JScrollPane(t),BorderLayout.SOUTH);
        add(p2,BorderLayout.SOUTH);
        b.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e) {
               if(f1 == null)
                 JOptionPane.showMessageDialog(null, "UNVALID NUMBER","",JOptionPane.ERROR_MESSAGE);
               else{
                   s2 = f1.getText();
                   m = Integer.parseInt(s2);
                   for(int i = 2 ; i<= m ;i++ ){
                     for (int j=2; j<=i;j++){
                       if(j==i){
                         t.append(""+i+"\n");//display the prime numbers in textarea
                       }
                       if(i%j==0)
                         break;  
                     }
                   } 
                 }
             }
          });
      }
  }