Código:
import java.awt.*; import java.awt.event.*; import javax.swing.*; public class Calculadora{ public static void main (String [] arg){ JFrame ventana = new JFrame("Calculadora"); ventana.setSize(400,600); ventana.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); ventana.setVisible(true); JButton boton0 = new JButton(" 0 "); boton0.setBackground( SystemColor.control ); boton0.setBounds(new Rectangle(50,50,100,75)); ventana.add(boton0); } }