public class DynamicStack { int capacity = 2; // Set the starting capacity of the stack int[] stack = new int[capacity]; // Initialise stack (array) int top = 0; // Track top of stack private void expand() { int length = size(); int[] newStack = new int[capacity * 2]; System.arraycopy(stack, 0, newStack, 0, length); stack = newStack; capacity *= 2; } private void shrink() { int length = size(); if (length <= (capacity / 4)) { // If the length of the stack is 1/4 the size of the capacity, half the capacity capacity = capacity / 2; int newStack[] = new int[capacity]; System.arraycopy(stack, 0, newStack, 0, length); // Copy old array into new array stack = newStack; // Reassign array } } public void push(int data) { // Push to the top of stack if (size() == capacity) { // If stack is full expand(); } stack[top] = data; // Add value to stack top++; } public int pop() { // Remove top value from stack if (isEmpty()) { // If stack is empty System.out.println("STACK IS EMPTY"); return 0; } else { top--; int data = stack[top]; stack[top] = 0; shrink(); return data; } } public int peek() { return stack[top - 1]; } public void show() { for (int i = 0; i < stack.length; i++) { System.out.print(stack[i] + " "); } } public int size() { return top; } public boolean isEmpty() { return top <= 0; } }