Java Stack

Stack is a LIFO ADT (Last in first out abstract data type) and a linear data structure. In a jar the items on top (i.e. items that went in last) come our first. In a LIFO ADT, items that go in last come our first.

Stacks are a very useful data structure. Although you have the possibility of creating your own stack data structure from Java code, it is a better idea to simply use the stack provided by Java.

Code Following code shows how to use Java’s stack:

import java.util.*;

public class UseStack{
  public static void main(String[] args) {
    Stack st = new Stack();
    st.push(new Integer(100));
    st.push("kcats");
    System.out.println("Stack contents: " + st);
    System.out.println(st.pop());
    st.pop();
    if (st.empty()) {
      st.push("stack");
    }
    System.out.println("Stack size: " + st.size());
    System.out.println(st.peek());
    System.out.println("Stack size: " + st.size());
  }
}

Output

Stack contents: [100, kcats]
kcats
Stack size: 1
stack
Stack size: 1

Explanation Stack is created by instantiating the Stack class. It accepts any object. Here I have added Integer and String. When you call System.out.print() on the stack object, its contents are printed in string format.

• push() adds an item
• pop() removes the top item
• peek() simply shows the first item without removing it
• empty() returns true if the stack is empty
• size() returns the size of the stack i.e. how many items does it contain