TextField与TextArea

在TextField中输入内容按回车显示在TextArea中，可是我按回车显示不了，这是怎么回事啊？求大家指教！！




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

public class ChatClient extends Frame {

TextField tfTxt = new TextField();
TextArea taContent = new TextArea();

public static void main(String[] args) {
new ChatClient().launchFrame();

}

public void launchFrame() {
setLocation(400,300);
this.setSize(300,300);
add(tfTxt,BorderLayout.SOUTH);
add(taContent,BorderLayout.NORTH);
pack();
this.addWindowListener(new WindowAdapter() {


@Override
public void windowClosing(WindowEvent e) {
System.exit(0);
}

});
tfTxt.addActionListener(new TFListener());
setVisible(true);

}

private class TFListener implements ActionListener {

public void actionPerformed(ActionEvent e) {
String str = tfTxt.getText().trim();
taContent.setText(str );
taContent.setText("");
}

}

}