Question

I was trying to implement a stack for my assignment. One of the method given is this: public T[] toArray(); I need help to implement this method. The class is a generic class. I am using ArrayList to implement my stack. ArrayList<T> stack is the data structure. I want to convert everything in the ArrayList to an array.
I am implementing the  public T[] toArray() interface given to me, so I can not use the JDK toArray method.

Answer 1

Here is the complete implementation of the Stack.java generic class using ArrayList<T> also implemented the toArray() method that returns the T[] type, also demonstrated below writing a driver method.

Let me know for any questions.

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import java.util.ArrayList;
import java.util.Random;

public class Stack<T> {

    private ArrayList<T> elements;

    public Stack() {
        elements = new ArrayList<T>();
    }


    public T[] toArray() {

        T[] array = (T[]) new Object[elements.size()];
        for (int i = 0; i < elements.size(); i++) {
            array[i] = elements.get(i);
        }

        return array;

    }

    public void push(T element) {
        elements.add(element);
    }

    public T pop() {
        if (elements.size() == 0) return null;
        T element = elements.get(elements.size() - 1);
        elements.remove(elements.size() - 1);
        return element;
    }

    public boolean isEmpty() {

        return elements.size() == 0;
    }

    public T peek(){
        if (elements.size() == 0) return null;
        T element = elements.get(elements.size() - 1);
        return element;
    }

    public static void main(String[] args) {

        Stack<Integer> numbers = new Stack<Integer>();
        Random random = new Random();
        for(int i=1;i<=5;i++)numbers.push(random.nextInt(10)+1);

        System.out.println("Convert elements to array");
        Object[] array = numbers.toArray();
        for(Object num:array) System.out.println(num);

        System.out.println("Pop out the elements");
        while (!numbers.isEmpty()) System.out.println(numbers.pop());
    }

}