public class CuentaBancaria {
 private String nombre;
 private double saldo;
 public CuentaBancaria(String n){
   nombre = n;saldo =0;
 }
 public String getNombre() {
    return nombre;
 }
 public double getSaldo() {
    return saldo;
 }
 public void setSaldo(double d) {
 DesignByContract.require(d >=0,
   new RuntimeException("d>=0"));
     saldo = d;
 }
 public void invertir(double c) {
   DesignByContract.require(c >0,
   new RuntimeException("c>0"));
   double old_saldo = saldo;
   saldo += c;
   DesignByContract.ensure(
     saldo == old_saldo + c,
     new RuntimeException(
     "saldo == old_saldo + c"));
 }
 public void retirar(double c) {
   DesignByContract.require(c >0,
   new RuntimeException("c>0"));
   DesignByContract.require(
   (saldo -c) >0,
   new RuntimeException("saldo-c>0"));
   double old_saldo = saldo;
   saldo -= c;
   DesignByContract.ensure(
     saldo == old_saldo - c,
     new RuntimeException(
     "saldo == old_saldo - c"));
   DesignByContract.ensure(
     saldo >=0,
     new RuntimeException(
     "saldo>=0"));
 }






}