Chapter 19, Problem 19.1PE

(Revising Listing 19.1) Revise the GenericStack class in Listing 19.1 to implement it using an array rather than an ArrayList. You should check the array size before adding a new element to the stack. If the array is full, create a new array that doubles the current array size and copy the elements front the current array to the new array.

Program Plan Intro

Revising Listing 19.1

Program Plan:

• Define the class named “GenericStack<E>”.
  • Declare appropriate variables to program.
  • Define constructors “GenericStack()” which assigns initial size of stack and “GenericStack(initialCapaciy)” which assigns size of the stack.
  • Define a method “push()” which pass “E o” as parameter.
    • Using “if” condition, check the value of “N” greater than “elements.length”.
      • Assign size of new array.
      • Copy old array into new array.
    • Return array elements.
  • Define a method “pop()” which pop out stack elements.
    • Return array elements.
  • Define a method “peek()” which returns top of the stack.
  • Define a method “isEmpty()” which returns “0”.
  • Define a method “getSize()” which returns size of the stack.
  • Define the main method.
    • Declare the GenericStack object “obj”, using the object insert elements into stack.
    • Using “while” loop, print the elements on screen.

Program Description Answer

The following JAVA code is to revise the “GenericStack” class which implements array rather than an “ArrayList”.

Explanation of Solution

Program:

//Class definition

class GenericStack<E>

{

/*Declaration of variables*/

public final static int INITIAL_SIZE = 16;

private E[] elements;

private int N;

/*Construct a stack with the default initial capacity */

public GenericStack()

{

//Assign initial size

this(INITIAL_SIZE);

}

/*Construct a stack with the specified initial capacity */

public GenericStack(int initialCapacity)

{

//Assign size

elements = (E[])new Object[initialCapacity];

}

/*Push a new element into the top of the stack */

public E push(E o)

{

//Condition

if (N >= elements.length)

{

//Assign array size into variable "t"

E[] t = (E[])new Object[elements.length * 2];

//Copy array elements

System.arraycopy(elements, 0, t, 0, elements.length);

//Assign "t" into "elements"

elements = t;

}

//Return statement

return elements[N++] = o;

}

/*Return and remove the top element from the stack*/

public E pop()

{

//Return statement

return elements[--N];

}

/*Return the top element from the stack */

public E peek()

{

//Return statement

return elements[N - 1];

}

/*Function definition to check empty*/

public boolean isEmpty()

{

//Return statement

return N == 0;

}

/*Return the number of elements in the stack */

public int getSize()

{

//Return statement

return N;

}

//Main method

public static void main(String[] args)

{

//Assign object to "GenericStack"

GenericStack<String> obj = new GenericStack<>();

//Push elements into stack

obj.push("London");

obj.push("Paris");

obj.push("Berlin");

//Print elements

System.out.print("Stack 1: ");

//Loop

while (!obj.isEmpty())

{

//Print statement

System.out.print(obj.pop() + " ");

}

//Print statement

System.out.println("\n");

}

}

Sample Output

Stack 1: Berlin Paris London