Two Stacks Implements A Deque

public class DequeStructure {
    Deque<Integer> stack1;
    Deque<Integer> stack2;
    public DequeStructure () {
        stack1 = new LinkedList<>();
        stack2 = new LinkedList<>();    
    }
    
    public void leftPush(int x) {
        stack1.push(x);
    }
    
    public void rightPush(int x) {
        stack2.push(x);
    }
    
    public int leftPop() {
        if (stack1.isEmpty() && stack2.isEmpty()) {
            return -1;
        }
        if (stack1.isEmpty()){
            shuffle();
        }
        return stack1.pop();
    }
    
    public int rightPop() {
        if (stack1.isEmpty() && stack2.isEmpty()) {
            return -1;
        }
        if (stack2.isEmpty()) {
            shuffle();
        }
        return stack2.pop();
    }
    
    // O(n) operations, very expensive!!
    private void shuffle() {
        if (stack1.isEmpty()) {
            while (!stack2.isEmpty()) {
                stack1.push(stack2.pop());
            }
        } else {
            while (!stack1.isEmpty()) {
                stack2.push(stack1.pop());
            }
        }
    }
}