Hi Friend,

Try the following codes:

1)ADT Stack:

import java.lang.*;
import java.io.*;
import java.util.*;

interface MyInterface {
int n = 20;

public void pop();

public void push();

public void peek();

public void display();
}

class StackImplementation implements MyInterface {
int arr[] = new int[n];
int top = -1;

public void push() {
try {
DataInputStream dis = new DataInputStream(System.in);
System.out.println("Enter Element");
int ele = Integer.parseInt(dis.readLine());
arr[++top] = ele;
} catch (Exception e) {
System.out.println("e");
}
}

public void pop() {
int popper = arr[top];
top--;
System.out.println("popped element " + popper);
}

public void peek() {
int popper = arr[top];
System.out.println("popped element " + popper);
}

public void display() {
if (top < 0) {
System.out.println("Stack is empty");
return;
} else {
String str = " ";
for (int i = 0; i <= top; i++)
str = str + " " + arr[i];
System.out.println("Elements are " + str);
}
}
}

class StackADT {
public static void main(String arg[]) throws IOException {
DataInputStream dis = new DataInputStream(System.in);
StackImplementation stk = new StackImplementation();
int menu = 0;
do {
System.out.println("1.push \n2.pop \n3.peek \n4.display \n5.Exit");
System.out.println();
System.out.print("Enter your choice: ");
menu = Integer.parseInt(dis.readLine());
switch (menu) {
case 1:
stk.push();
break;
case 2:
stk.pop();
break;
case 3:
stk.peek();
break;
case 4:
stk.display();
break;
case 5:
System.exit(0);
}
} while (menu <= 5);
System.out.println();
}
}

continue..

2)Polymorphism:

class Vehicle {
void test(){}
}
class Bus extends Vehicle{
void test()
{
System.out.println("I am a bus");
}
}
class Car extends Vehicle{
void test()
{
System.out.println("I am a car");
}
}
class Bike extends Vehicle{
void test()
{
System.out.println("I am a bike");
}
}
public class Polymorphism{
public static void main(String[]args){
Vehicle[] v = new Vehicle[3];
v[0]= new Bus();
v[1]=new Car();
v[2]=new Bike();
for(int i=0;i<v.length;i++){
v[i].test();
}

}
}

Thanks