Administrasi Kartu Pintar

 Class KartuPintar

public class KartuPintar{
  public static final int SALDO_AWAL=10000;
  //attribute
  private String id;
  private int saldo;

  //constructor
  public KartuPintar(){
    id="0000";
    saldo=SALDO_AWAL;
  }

  //constructor
  public KartuPintar(String id, int saldo){
    this.id=id;
    this.saldo=saldo;
  }
  //implementor
  public void topUp(){
    saldo += SALDO_AWAL;
  }
  //implementor
  public void topUp(int value){
    saldo +=value;
  }
  public String toString(){
    return id+"->saldo: " + saldo;
  }
  //getter
  public String getId(){
    return id;
  }
  //getter
  public int getSaldo(){
    return saldo;
  }
  //implementor
  public void debet(int value){
    if(checkSaldo(value))
      saldo -=value;
    else
      System.out.println("Saldo Anda Tidak Cukup !");
  }
  private boolean checkSaldo(int value){
    return ((saldo-value)>=0);
  }
}

CounterKartuPintar

import java.util.*;
public class CounterKartuPintar{
  private Vector daftarKartu=new Vector();

  public void kartuBaru(KartuPintar kartuBaru){
    daftarKartu.add(kartuBaru);
  }
  public void viewAllKartu(){
    for(KartuPintar kartu:daftarKartu)
      System.out.println(kartu);
  }

  public void topUp(String idKartu, int value){
   int idx=cariKartu(idKartu);
    if(idx!=-1){
      daftarKartu.elementAt(idx).topUp(value);
      System.out.println("Id Kartu: " +idKartu + " BERHASIL di topUp");
      System.out.println("Saldo Saat ini: "); 
      cetakSaldo(idKartu);
    }
    else
      System.out.println("No Kartu Tidak Ada !");

  }
  public void debet(String idKartu, int value){

  }
  public void cetakSaldo(String id){
    int idx=cariKartu(id);
    if(idx!=-1){
      System.out.println(daftarKartu.elementAt(idx));
    }
    else
      System.out.println("No Kartu Tidak Ada !");
  }
  private int cariKartu(String id){
    int idx=-1;
    int i=0;
    do{
      if(daftarKartu.elementAt(i).getId().equals(id))
      {
        idx=i;
        i=daftarKartu.size();
      }
      i++;
    }while(i