StackAsLinkedList.java

public class StackAsLinkedList { 
  
    StackNode root; 
  
    static class StackNode { 
        int data; 
        StackNode next; 
  
        StackNode(int data) 
        { 
           this.data=data;
           this.next=null;//Constructor here 
        } 
    } 
    
	
    public boolean isEmpty() 
    { 
        if(root==null) return true;
        else return false;//Write your code here for the condition if stack is empty. 
    } 
  
    public void push(int data) 
    { 
        StackNode t=new StackNode(data);
        if(root==null)
            {
                root=t;}
                
                else{
                    t.next=root;
                    root=t;//Write code to push data to the stack. 
    } }
  
    public int pop() 
    { 	
        if(isEmpty())
        {
            System.out.println("Stack Underflow");
            return 0;
        }

        int t=root.data;
        root=root.next;
        return t;
	//If Stack Empty Return 0 and print "Stack Underflow"
        //Write code to pop the topmost element of stack.
	//Also return the popped element 
    } 
  
    public int peek() 
    { 
        if(isEmpty())
            {
                return 0;
            }
            else return root.data;//Write code to just return the topmost element without removing it.
    } 
  
	//Driver code
    public static void main(String[] args) 
    { 
  
        StackAsLinkedList sll = new StackAsLinkedList(); 
  
        sll.push(10); 
        sll.push(20); 
        sll.push(30); 
  
        System.out.println(sll.pop() + " popped from stack"); 
  
        System.out.println("Top element is " + sll.peek()); 
    } 
}