진법변환기 gui

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

class BtnDigitListener implements ActionListener {
	public void actionPerformed(ActionEvent e) {
		JButton btn = (JButton)e.getSource();
		String digits = NsystemWin.tf.getText();
		if (digits.equals("0"))
			digits = btn.getText();
		else
			digits = digits + btn.getText();
		NsystemWin.tf.setText(digits);
	}
}

class BtnModelListener implements ActionListener {
	static int state = 10;
	
	public void actionPerformed(ActionEvent e) {
		JButton btn = (JButton)e.getSource();
		String value = NsystemWin.tf.getText();
		String mode = btn.getText();
		
		switch(mode.toUpperCase()) {
		case "BIN":
			NsystemWin.tf.setText(convert(value, state, 2));
			state = 2;
			break;
		case "OCT":
			NsystemWin.tf.setText(convert(value, state, 8));
			state = 8;
			break;
		case "DEC":
			NsystemWin.tf.setText(convert(value, state, 10));
			state = 10;
			break;
		case "HEX":
			NsystemWin.tf.setText(convert(value, state, 16));
			state = 16;
			break;
		case "C":
			int dec_val = Integer.parseInt(value, state);
			dec_val = dec_val/state;
			value = convert(Integer.toString(dec_val), 10, state);
			NsystemWin.tf.setText(value);
			break;
		default:
			System.out.println("not available");
			break;
		}
		
		NsystemWin.Label.setText("  "+Integer.toString(state) + "진수");
	}
	
	private String convert(String value, int from, int to) {
		String convert_val;
		
		int dec_val = Integer.parseInt(value, from);
		
		switch (to) {
		case 10:
			convert_val = Integer.toString(dec_val);
			break;
		case 2:
			convert_val = Integer.toBinaryString(dec_val);
			break;
		case 8:
			convert_val = Integer.toOctalString(dec_val);
			break;
		case 16:
			convert_val = Integer.toHexString(dec_val);
			break;
		default:
			System.out.println("잘못된 입력");
			return value;
		}
		
		return convert_val;
	}
}

class NsystemWin extends JFrame {
	private String[] btnNames = {
		"0", "1", "2", "3", "4",
		"5", "6", "7", "8", "9",
		"Bin", "Oct", "Dec", "Hex", "C"
	};
	static JLabel Label;
	static TextField tf;
	
	public NsystemWin() {
		initLayout();
		
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		this.setTitle("Numeric System");
		this.setSize(300, 200);
		this.setMinimumSize(new Dimension(300, 200));
		this.setVisible(true);
	}
	
	private void initLayout() {
		this.getContentPane().setLayout(new BorderLayout());
		
		JPanel panel1 = new JPanel();
		JPanel panel2 = new JPanel();
		panel1.setLayout(new GridLayout(1, 2));
		panel2.setLayout(new GridLayout(3, 5));
		
		tf = new TextField();
		Font font = new Font("Consolas", Font.PLAIN, 20);
		tf.setFont(font);
		tf.setText("0");
		
		Label = new JLabel();
		Label.setHorizontalAlignment(JLabel.CENTER);
		Label.setSize(30, 30);
		Label.setText("10진수");
		
		panel1.add(Label);
		panel1.add(tf);
		
		BtnDigitListener digitListener = new BtnDigitListener();
		BtnModelListener modeListener = new BtnModelListener();
		
		for (int i =0; i<btnNames.length; i++) {
			JButton btn = new JButton(btnNames[i]);
			if (i<10)
				btn.addActionListener(digitListener);
			else
				btn.addActionListener(modeListener);
			panel2.add(btn);
		}
		
		this.getContentPane().add(panel1, BorderLayout.NORTH);
		this.getContentPane().add(panel2, BorderLayout.CENTER);
	}
}

public class Ex extends JFrame {
	public static void main(String[] args) {
		NsystemWin nsw = new NsystemWin();
	}
}