Coding Java "Ketupat"

Selamat mencoba yah guys :)


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

class Ketupat extends JFrame implements ActionListener
{
private JTextArea output;
private JButton btnProses, btnTutup, btnHapus;
private JTextField size;

public Ketupat(){

JPanel panel_1=new JPanel();
panel_1.setLayout(new FlowLayout());
panel_1.add(btnTutup=new JButton("Tutup"));
panel_1.add(btnHapus=new JButton("Hapus"));

JScrollPane scroll = new JScrollPane(output=new JTextArea());
output.setFont(new Font("Arial",0,14));
output.setLineWrap(true);
output.setWrapStyleWord(true);
scroll.setPreferredSize(new Dimension(300, 100));
JPanel panel_2=new JPanel();
panel_2.setLayout(new BorderLayout());
panel_2.add(scroll);
output.setEditable(false);

JPanel panel_3=new JPanel();
panel_3.setLayout(new FlowLayout());
panel_3.add(new JLabel("Silahkan masukkan angka 0-9 "));
panel_3.add(size=new JTextField(3));
panel_3.add(btnProses=new JButton("Proses"));

setLayout(new BorderLayout());
add(panel_2,"Center");
add(panel_1,"South");
add(panel_3,"North");

btnProses.addActionListener(this);
btnHapus.addActionListener(this);
btnTutup.addActionListener(this);
}

public void actionPerformed(ActionEvent e){
String str="";
if(e.getSource()==btnProses){
int i,j,k;
try{
int ukuran=Integer.parseInt(size.getText().trim());
if((ukuran >= 0)&&(ukuran < 10)){ for(i=1;i<=ukuran;i++){ for(j=ukuran;j>=i;j--)
str+=" ";
for(k=1;k<=i;k++) str+="/\\"; str+="\n"; } for(i=ukuran;i>=1;i--){
for(j=i;j<=ukuran;j++) str+=" "; for(k=i;k>=1;k--)
str+="\\/";
str+="\n";
}

output.setText(str);
}else{
JOptionPane.showMessageDialog(null,"Anda salah input!!!","Warning",
JOptionPane.WARNING_MESSAGE);
}
}catch(Exception ex){
JOptionPane.showMessageDialog(null,"Error--"+ex.toString(),"Error",
JOptionPane.ERROR_MESSAGE);
}
}

if(e.getSource()==btnTutup){
JOptionPane.showMessageDialog(null,"--- Terima kasih ---\n by : Team Lab TI Universitas Gunadarma",
"Thank you", JOptionPane.INFORMATION_MESSAGE);
System.exit(0);
}

if(e.getSource()==btnHapus){
output.setText(null);
size.setText(null);
str="";
}
}

public static void main(String[] args){
Ketupat frame = new Ketupat();
frame.pack();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle("Galih Mahrandy");
frame.setVisible(true);

}
}

Jangan lupa yah coment-nya :)