JTextArea : setText, getText and append methods

import javax.swing.*;
import java.awt.*;

import java.awt.event.*; // step 1

public class JTextAreaDemo extends JFrame //step 2
                             implements ActionListener{
  
  private JTextArea ta1 = new JTextArea(10,20);
  private JButton btn = new JButton("Add");
  private JButton btn2 = new JButton("Append");
  private JButton btn3 = new JButton("Get text in TextArea");

  public JTextAreaDemo() {

    getContentPane().setLayout(new FlowLayout());
    getContentPane().add(ta1);
    getContentPane().add(btn);
    getContentPane().add(btn2);
    getContentPane().add(btn3);
       
    btn.addActionListener(this);//step 4:
    btn2.addActionListener(this);
    btn3.addActionListener(this);
    
  } //end constructor
  
  public void actionPerformed(ActionEvent teckyong){//step 3
    
      if (teckyong.getSource() == btn){
        ta1.setText("ABC"); // Add text, overwrite the previous
      } //end if
      else if (teckyong.getSource() == btn2){
        ta1.append("ABC\n");
      }
      else if (teckyong.getSource() == btn3){
        String s = ta1.getText(); // Get what is in the TextArea
        JOptionPane.showMessageDialog(null,s);
      }
    
  } //end actionPerformed

  public static void main(String[] args) {
    JTextAreaDemo f = new JTextAreaDemo();
    f.setTitle("OOPG");
    f.setSize(300, 300);
    f.setVisible(true);

  } //end main
} //end class