Question

StackBox

Implement our own stack class patterned after Java's Stack class. Start with a generic class that uses an ArrayList for storage of the elements:

public class StackBox<E>
{
ArrayList<E> stack = new ArrayList<E>();
}

Implement the following methods in StackBox:

boolean empty()
Tests if this stack is empty.

E push(E item)
Pushes an item onto the top of this stack. Returns item pushed.

E pop()
Removes the object at the top of this stack and returns that object as the value of this function. Throws EmptyStackException if empty.

E peek()
Looks at the object at the top of this stack without removing it from the stack. Throws EmptyStackException if empty.

Refer to my slides in class for exact specifications details for each of these methods. For full marks your StackBox must throw exceptions as specified above. Now create an instance of StackBox that holds Integers. Create a menu that looks like this to test your StackBox:

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

Marking (The Program will look like as below):-

Defining StackBox as a generic class. [ 1 mark ].

WARNING - your program will NOT be accepted if you don't create and use a generic class StackBox as defined for this assignment.

Implementing the four Stack methods: empty, push. pop, and peek as per their specification including throwing exceptions if specified. [ 2 marks ]

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 1

Enter an Integer you want to add to the StackBox >>1

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 1

Enter an Integer you want to add to the StackBox >>2

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 1

Enter an Integer you want to add to the StackBox >>3

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 3

The element currently at the top of the stack is 3   [ 2 mark for correct peek behavior ]

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 2

The element 3 was removed from the top of the stack box.

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 2

The element 2 was removed from the top of the stack box.

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 2

The element 1 was removed from the top of the stack box.

[ 7 MARKS for correct push/pop behavior ]

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 2

Stack is empty. Caught EmptyStackException. [ 1 MARK ]

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 3

Stack is empty. Caught EmptyStackException. [ 1 MARK ]

=[==[==[=[=================================]=]==]==]=

=[==[==[=[ Welcome to StackBox ]=]==]==]=

=[==[==[=[=================================]=]==]==]=

Choose...

1. Push a (Integer) to our stack box.

2. Pop a (Integer) off our stack box.

3. Peek at top of the stack.

4. Exit

>> 4

Answer 1

StackBox.java

import java.util.ArrayList;
import java.util.EmptyStackException;
import java.util.Scanner;

public class StackBox<E>
{
   ArrayList<E> stack = new ArrayList<E>();
  
   //Tests if this stack is empty.
   boolean empty()
   {
       boolean result = stack.isEmpty();
       return result;
   }
  
   //Pushes an item onto the top of this stack. Returns item pushed.
   E push(E item)
   {
       stack.add(item);
       return item;
   }
  
   //Removes the object at the top of this stack and returns that object as the value of this function.
   //Throws EmptyStackException if empty.
   E pop()
   {
       if(empty())
       {
           throw new EmptyStackException();
       }
       E last_element = stack.get(stack.size() - 1); // the most recently pushed element is at the last index. SO we try to access it.
       stack.remove(stack.size() - 1); // Now remove that element from stack
return last_element;
   }
  
   //Looks at the object at the top of this stack without removing it from the stack.
   //Throws EmptyStackException if empty.
   E peek()
   {
       if(empty())
       {
           throw new EmptyStackException();
       }
       return stack.get(stack.size() - 1);
   }
  
   public static void main(String args[])
   {
       //Now create an instance of StackBox that holds Integers.
       StackBox<Integer> s = new StackBox<Integer>();
      
       //to take input we use scanner object
       Scanner scan = new Scanner(System.in);
       int input;
      
       while(true)
       {  
           //Create a menu that looks like this to test your StackBox:
           System.out.println("=[==[==[=[=================================]=]==]==]=");
           System.out.println("=[==[==[=[ Welcome to StackBox ]=]==]==]=");
           System.out.println("=[==[==[=[=================================]=]==]==]=");
           System.out.println("Choose...");
           System.out.println("1. Push a (Integer) to our stack box.");
           System.out.println("2. Pop a (Integer) off our stack box.");
           System.out.println("3. Peek at top of the stack.");
           System.out.println("4. Exit");
          
           input = scan.nextInt();
          
           switch(input)
           {
               case 1:
                   System.out.println("Enter an Integer you want to add to the StackBox >> ");
                   input = scan.nextInt();
                   s.push(input);
                   break;
                  
               case 2:
                   try
                   {
                       System.out.println("The element "+ s.pop() +" was removed from the top of the stack box.");
                   }
                   catch(EmptyStackException e)
                   {
                       System.out.println("Stack is empty. Caught EmptyStackException. ");
                   }          
                   break;
                  
               case 3:
                   try
                   {
                   System.out.println("The element currently at the top of the stack is "+s.peek());
                   }
                   catch(EmptyStackException e)
                   {
                       System.out.println("Stack is empty. Caught EmptyStackException. ");
                   }
                   break;
                  
               case 4:
                   scan.close();
                   return;
                  
               default:
                   System.out.println("Invalid option. Try again");
                   break;
           }
       }  
   }
}

Sample I/O and output