Erro de Calculadora

setSize( 250, 400 );
    setVisible( true );
    
}

import java.awt.Button;
import java.awt.Container;
import java.awt.Event;
import java.awt.Font;
import java.awt.TextField;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class CalculadoraDesafio extends JFrame implements WindowListener,
		ActionListener, KeyListener {

	/** 
* 
*/
	private static final long serialVersionUID = 1L;
	TextField txtResult;
	boolean new_entry;
	char teste;
	double arg1, arg2;
	float j, i, n;

	public CalculadoraDesafio() {
		super("Calculadora Java");
		Container c = getContentPane();
		setLayout(null);
		super.setIconImage((new ImageIcon("src/calculadora-java.png")
				.getImage()));
		JLabel campo = new JLabel();
		campo.setBounds(10, 0, 210, 80);
		campo.setFont(new Font("Times New Roman", Font.PLAIN, 12));
		c.add(campo);

		txtResult = new TextField("0");
		txtResult.setBounds(10, 100, 200, 25);
		txtResult.setText(new Float(n).toString());
		add(txtResult);

		JButton CE = new JButton("CE");
		JButton Editar = new JButton("Editar");
		JButton Exibir = new JButton("Exibir");
		JButton Ajuda = new JButton("Ajuda");
		JButton Soma = new JButton("+");
		JButton Sub = new JButton("-");
		JButton Mul = new JButton("x");
		JButton Div = new JButton("/");
		JButton botaoc = new JButton("c");
		JButton botao0 = new JButton("0");
		JButton botao1 = new JButton("1");
		JButton botao2 = new JButton("2");
		JButton botao3 = new JButton("3");
		JButton botao4 = new JButton("4");
		JButton botao5 = new JButton("5");
		JButton botao6 = new JButton("6");
		JButton botao7 = new JButton("7");
		JButton botao8 = new JButton("8");
		JButton botao9 = new JButton("9");
		JButton igual = new JButton("=");
		JButton virgula = new JButton(",");
		JButton porcentagem = new JButton("%");

		Soma.setBounds(160, 130, 50, 30);
		Sub.setBounds(160, 160, 50, 30);
		Mul.setBounds(160, 190, 50, 30);
		Div.setBounds(110, 220, 50, 30);
		botao0.setBounds(10, 220, 50, 30);
		botaoc.setBounds(60, 220, 50, 30);
		botao2.setBounds(60, 190, 50, 30);
		botao1.setBounds(10, 190, 50, 30);
		botao3.setBounds(110, 190, 50, 30);
		botao4.setBounds(10, 160, 50, 30);
		botao5.setBounds(60, 160, 50, 30);
		botao6.setBounds(110, 160, 50, 30);
		botao7.setBounds(10, 130, 50, 30);
		botao8.setBounds(60, 130, 50, 30);
		botao9.setBounds(110, 130, 50, 30);
		Ajuda.setBounds(16, 10, 70, 20);
		Exibir.setBounds(76, 10, 70, 20);
		Editar.setBounds(136, 10, 70, 20);
		virgula.setBounds(60, 250, 50, 30);
		porcentagem.setBounds(110, 250, 50, 30);
		igual.setBounds(160, 220, 50, 60);
		CE.setBounds(10, 250, 50, 30);

		c.add(botao0);
		c.add(botao1);
		c.add(botao2);
		c.add(botao3);
		c.add(botao4);
		c.add(botao5);
		c.add(botao6);
		c.add(botao7);
		c.add(botao8);
		c.add(botao9);
		c.add(botaoc);
		c.add(Soma);
		c.add(Sub);
		c.add(Mul);
		c.add(Div);
		c.add(igual);
		c.add(Ajuda);
		c.add(Exibir);
		c.add(Editar);
		c.add(virgula);
		c.add(porcentagem);
		c.add(CE);

		setSize(250, 400);
		setVisible(true);

	}

	public boolean action(Event evt, Object arg) {
		if (evt.target instanceof Button) {
			arg1 = arg2 = 0.0;
			char keypress = ((String) arg).charAt(0);
			if ((keypress == '/') || (keypress == '*') || (keypress == '+')
					|| (keypress == '-')) {
				teste = keypress;
				System.out.println(teste);
			}
			if (((keypress >= '0') && (keypress <= '9')) || (keypress == '.')) {
				if (new_entry) {
					if ((teste == '/') || (teste == '*') || (teste == '+')
							|| (teste == '-')) {
						txtResult.setText((String) arg);
					} else {
						txtResult.setText((String) arg);
					}
					new_entry = false;
				} else {
					if ((teste == '/') || (teste == '*') || (teste == '+')
							|| (teste == '-')) {
						txtResult.setText(txtResult.getText() + ((String) arg));
					} else {
						txtResult.setText(txtResult.getText() + ((String) arg));
					}
				}
			}
			if (arg.equals("=")) {
				float i = Float.valueOf(txtResult.getText()).floatValue();
				float j = Float.valueOf(txtResult.getText()).floatValue();
				float n;

				if (teste == '+') {
					n = i + j;

					txtResult.setText(new Float(n).toString());
				} else if (teste == '-') {
					n = i - j;
					txtResult.setText(new Float(n).toString());
				} else if (teste == '*') {
					n = i * j;

					txtResult.setText(new Float(n).toString());
				} else if (teste == '/') {
					n = i / j;

					txtResult.setText(new Float(n).toString());
				}
			} else if (arg.equals("Reset"))

			{
				keypress = ((String) arg).charAt(0);
				txtResult.setText("");
				teste = keypress;
				txtResult.setText("");

			}
		}
		return new_entry;

	}

	public static void main(String args[]) {
		CalculadoraDesafio obj = new CalculadoraDesafio();

	}

	public void windowActivated(WindowEvent e) {
		// TODO Auto-generated method stub

	}

	public void windowClosed(WindowEvent e) {
		// TODO Auto-generated method stub

	}

	public void windowClosing(WindowEvent e) {
		// TODO Auto-generated method stub

	}

	public void windowDeactivated(WindowEvent e) {
		// TODO Auto-generated method stub

	}

	public void windowDeiconified(WindowEvent e) {
		// TODO Auto-generated method stub

	}

	public void windowIconified(WindowEvent e) {
		// TODO Auto-generated method stub

	}

	public void windowOpened(WindowEvent e) {
		// TODO Auto-generated method stub

	}

	public void actionPerformed(ActionEvent e) {
		// TODO Auto-generated method stub

	}

	public void keyPressed(KeyEvent e) {
		// TODO Auto-generated method stub

	}

	public void keyReleased(KeyEvent e) {
		// TODO Auto-generated method stub

	}

	public void keyTyped(KeyEvent e) {
		// TODO Auto-generated method stub

	}
}