Something

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package gcode.chapter3;

/**
 *
 * 
 */
public class LinkList {

    public Node head,tail;   /* Point to head and tail of list */
    
    /* Constructor */
    public LinkList(){
        head = null;
        tail = null;
    }
    
    /* isEmpty */
    public boolean isEmpty(){
        return head==null;
    }

    /* To insert at the beginning of the link list (push) */
    public void insertAtHead(int d){
        Node newNode = new Node(d); /* Create a new node */
        /* First entry */
        if(isEmpty()){
          tail = newNode;   /* We want to make the tail look at this node */  
          newNode.next = null;
        }
        newNode.next = head;
        head = newNode;
    }
    
    /* To insert at the end of the list (enqueue) */
    public void insertAtTail(int d){
        Node newNode = new Node(d);
        /* First entry */
        if(isEmpty()){
            head = newNode;
            tail = newNode;
            newNode.next = null;
        }
        tail.next = newNode;  /* Add in new node to end */
        tail = tail.next;     /* Move tail to the end */  
    }
    
    
    /* To delete the first of the link list (pop, dequeue) */
    public int removeAtHead(){
        Node tmp = head;
        head = head.next; /* Move head over */
        tmp.next = null;
        return tmp.data;
    }
    
    public void displayList(){
        Node tracker;
        System.out.println("displaying list");
        for(tracker = head; tracker != null; tracker=tracker.next){
            tracker.displayNode();
        }
        System.out.println("---");
        
    }
    

    
    
    
}


/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package gcode.chapter3;

/**
 */
public class MyStack {
    public Node top, minptr;
    public int min;
    public LinkList l;
    
    /* Constructor */
    public MyStack(){
        l = new LinkList();
        top = l.head;
        minptr = top;
        min = 999999; /* large value */
    }
    
    /* push */
    public void push(int d){
        l.insertAtHead(d);
        if(d < min){
            min = d;       /* Replace min */
            minptr = top;  /* Make it point to the top of stack */
        }
    }
    
    /* pop */
    public int pop(){
        return l.removeAtHead();
    }
    
    /* peek at top */
    public int top(){
        return top.data;
    }
    
    public boolean isEmpty(){
        return l.isEmpty();
    }
    
    public void displayStack(){
        System.out.println("Displaying stack...");
        l.displayList();
    }

    public int getMinimum(){
        return minptr.data;
    }
    
    
        /* Main function */
    public static void main(String[] args) {
        
        MyStack s = new MyStack();
        
        s.push(10);
        s.push(20);
        s.push(30);
        
        s.displayStack();
        
        s.pop();
        
        s.displayStack();
        
        return;
    }
}



/* OUTPUT */
Displaying stack...
displaying list
---
Displaying stack...
displaying list
---
30 20 10 20 10 BUILD SUCCESSFUL (total time: 1 second)