parseFloat

import java.awt.Color;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JTextField;

public class Exemplo0904 extends JFrame implements ActionListener {
	JLabel L1, L2, L3;
	JButton B1, B2, B3, B4, B5;
	JTextField T1,T2,T3;

	public static void main(String args[])
	{
		JFrame Janela = new Exemplo0904();
		Janela.show();
		
		//rotina para fechar a janela:
		WindowListener x = new WindowAdapter()
		{
			public void windowClosing(WindowEvent e)
			{
				System.exit(0);
			}
		};
		Janela.addWindowListener(x);
	}

	Exemplo0904()
	{
		setTitle("Calculadora");  //Texto no título do formulário
		setSize(290,290);	//dimensoes da janela
		setLocation(50,50); //canto esquerdo e topo da janela
		getContentPane().setBackground(new Color(150,150,150)); //Definição da cor de fundo 
		getContentPane().setLayout(new GridLayout(3,4)); //definição do layout
		
		//Declarações de componetes, inicialização...
		L1 = new JLabel("Num.1");	
		L1.setForeground(Color.black);
		L1.setFont(new Font("",Font.BOLD,12));
		L2 = new JLabel("Num.2");
		L2.setForeground(Color.black);
		L2.setFont(new Font("", Font.BOLD, 12));
		L3 = new JLabel("Total");
		L3.setFont(new Font("", Font.BOLD, 12));
		B1 = new JButton ("+");
		B1.addActionListener(this);
		B2 = new JButton ("-");
		B2.addActionListener(this);
		B3 = new JButton ("x");
		B3.addActionListener(this);
		B4 = new JButton ("/");
		B4.addActionListener(this);
		B5 = new JButton ("Limpar");
		B5.addActionListener(this);
		B5.setBackground(Color.black);
		B5.setForeground(Color.white);
		T1 = new JTextField();
		T2 = new JTextField();
		T3 = new JTextField();
		T3.setEditable(false); //somente leitura, não é possivel inserir dados
		getContentPane().add(L1);
		getContentPane().add(T1);
		getContentPane().add(B1);
		getContentPane().add(B2);
		getContentPane().add(L2);
		getContentPane().add(T2);
		getContentPane().add(B3);
		getContentPane().add(B4);
		getContentPane().add(L3);
		getContentPane().add(T3);
		getContentPane().add(B5);
	}
	public void actionPerformed(ActionEvent e)
	{
		if (e.getSource()==B5) // evento clique no B5 (botão limpar) atribui valores ""
		{						// nas textfields
			T1.setText(""); T2.setText(""); T3.setText("");
			return;
		}
		
		float N1=0,N2=0,result=0;
		
		/*	try
		{N1 = Float.parseFloat(T1.getText());
		N2 = Float.parseFloat(T2.getText());
		
	}
		catch (NumberFormatException erro)
		{
			T3.setText("Erro");
			return;
		}*/
		if (e.getSource()==B1)
			result = N1 + N2;
		if (e.getSource()==B2)
			result = N1 - N2;
		if (e.getSource()==B3)
			result = N1 * N2;
		if (e.getSource()==B4)
			result = N1 / N2;
		T3.setText ("" + result);
	}
}