Question

Complete StackArray.java code below.

Use StackArrayDemo.java to test your implementation of StackArray.java.

StackArray.java below.

public class StackArray <T> {

public static int CAPACITY = 100;

private final T[] elements;

private int topIndex;

// Constructor

public StackArray() {

// Initialize elements

// Initialize topIndex to -1

}

public T peek() {

// If topIndex is less than zero, return null.

// Otherwise, return element from top of the stack.

}

public T pop() {

// If topIndex is less than zero, return null.

// Otherwise return element from top of the stack, and decrement topIndex

}

public void push(T obj) {

// Push obj into top of the stack

// And, increment topIndex

}

public int getStackSize() {

// Return stack size, i.e., number of elements

}

@Override

public String toString() {

String s = "The stack is: ";

for (int i = topIndex; i >= 0; i--)

s += elements[i] + " ";

return s;

}

}//end class StackArray

Use StackArrayDemo.java below to test your code.

public class StackArrayDemo {

public static void main(String [] args) {

StackArray a = new StackArray();

int score = 0;

if (a.peek() == null)

score += 10;

else

System.out.println("Check peek()");

a.push("Orange");

System.out.println(a);

a.push("Apple");

System.out.println(a);

a.push("Guava");

System.out.println(a);

if (a.peek().equals("Guava"))

score += 10;

else

System.out.println("Check push()");

a.pop();

System.out.println(a);

a.pop();

System.out.println(a);

if (a.peek().equals("Orange"))

score += 10;

else

System.out.println("Check pop()");

a.push("Mango");

System.out.println(a);

if (a.getStackSize() == 2)

score += 10;

else

System.out.println("Check getStackSize()");

System.out.printf("Your score is %d/40\n", score);

}

}

Answer 1

public class StackArray<T> {
    public static int CAPACITY = 100;
    private final T[] elements;
    private int topIndex;

    // Constructor
    public StackArray() {
        elements = (T[]) new Object[CAPACITY];
        topIndex = -1;
    }

    public T peek() {
// If topIndex is less than zero, return null.
// Otherwise, return element from top of the stack.
        if (topIndex < 0)
            return null;
        return elements[topIndex];
    }

    public T pop() {
// If topIndex is less than zero, return null.
// Otherwise return element from top of the stack, and decrement topIndex
        if (topIndex < 0)
            return null;
        return elements[topIndex--];
    }

    public void push(T obj) {
// Push obj into top of the stack
// And, increment topIndex
        elements[++topIndex] = obj;
    }

    public int getStackSize() {
        return topIndex+1;
    }

    @Override
    public String toString() {
        String s = "The stack is: ";
        for (int i = topIndex; i >= 0; i--)
            s += elements[i] + " ";
        return s;
    }
}//end class StackArray