Programa de Menu con pilas

Programa:

public class Menu {
    public static void main(String[] args) {
         Pila op1= new Pila();
         Mostrar op2 = new Mostrar();
        Eliminar op3 = new Eliminar();
        int num=0;
        do{
        System.out.println("\t Operaciones con Pilas \t");
        System.out.println("1.- INSERTAR");
        System.out.println("2.- MOSTRAR");
        System.out.println("3.- ELIMINAR");
        System.out.println("4.- SALIR");
        System.out.println("Eliga su operacion");
       
        Scanner capt =new Scanner(System.in);
              num=capt.nextInt();
        switch(num){
            case 1:
                System.out.println("Insertando");
                op1.Pilam();
                break;
           case 2:
                System.out.println("Mostrando");
                op2.Most();
                break;
           case 3:
                System.out.println("Eliminando");
                op3.Elim();
               
                break;
            case 4:
                System.out.println("Saliendo");
num=7;
break;
        }
    }
         while(num<6);}
}
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public class Pila {
  int NUM=4;
        int pila[]=new int[NUM];
    int tope;
   public void Pilam(){
  
      
        System.out.println("Por Favor Introduzca datos a capturar");
        Scanner captura=new Scanner(System.in);
        for ( tope = 0; tope < NUM; tope++) {
          
            pila[tope]=captura.nextInt();
        }
       
    }
}
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public class Mostrar {
     Pila opm=new Pila();
    public void Most(){
       
        for (opm.tope = 3; opm.tope >=0; opm.tope--) {
            System.out.println("Datos Capturados "+opm.pila[opm.tope]);
        }
    }
}
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public class Eliminar {
    Pila opm1= new Pila();
    public void Elim(){
        if (opm1.tope<5) {
            opm1.tope--;
           for (int i = 3; i >=0; i--) {
            System.out.println(" "+opm1.pila[i]);
        }
    }
    }
}