How to implement stack data structure in Java without using collections.

Implementing Stack without using Collections 

// Create interface called Stack

public interface Stack {

void push(Object value);

Object pop();

int length();

}

// Create class implementing Stack interface named StackImpl

public class StackImpl implements Stack {

private Node head;

private int length;

@Override

public void push(Object value) {

Node node = new Node(value);

if (head == null) {

head = node;

} else {

node.next = head;

head = node;

}

length++;

}

@Override

public Object pop() {

Object result = null;

if (head != null) {

result = head.value;

head = head.next;

length--;

}

return result;

}

public int length() {

return length;

}

private class Node {

private Object value;

private Node next;

public Node(Object value) {

super();

this.value = value;

}

}

}

// Test StackImpl

public class StackTest {

public static void main(String args[]) {

Stack stack = new StackImpl();

stack.push("stack 1");

stack.push("stack 2");

stack.push("stack 3");

stack.push("stack 4");

stack.push("stack 5");

stack.push("stack 6");

System.out.println(stack.pop() + "--"+stack.length());

System.out.println(stack.pop() + "--"+stack.length());

System.out.println(stack.pop() + "--"+stack.length());

}

}