Table of Contents

Java Stack Class

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Introduction

Stack is a subclass of Vector that implements a standard last-in, first-out stack.

Stack only defines the default constructor, which creates an empty stack. Stack includes all the methods defined by Vector, and adds several of its own.

The Java Stack class represents a last-in-first-out (LIFO) stack of objects.

When a stack is first created, it contains no items.
In this class, the last element inserted is accessed first.

Class declaration

Following is the declaration for java.util.Stack class −

public class Stack<E>
   extends Vector<E>

Class constructors

Sr.No.	Constructor & Description
1	Stack() This constructor creates an empty stack.

Class methods

Sr.No.	Method & Description
1	boolean empty() This method tests if this stack is empty.
2	E peek() This method looks at the object at the top of this stack without removing it from the stack.
3	E pop() This method removes the object at the top of this stack and returns that object as the value of this function.
4	E push(E item) This method pushes an item onto the top of this stack.
5	int search(Object o) This method returns the 1-based position where an object is on this stack.

Methods inherited

This class inherits methods from the following classes −

java.util.Vector
java.util.Collection
java.util.Object
java.util.List

Example

The following program illustrates several of the methods supported by Stack collection −

import java.util.*;
public class StackDemo {

   static void showpush(Stack st, int a) {
      st.push(new Integer(a));
      System.out.println("push(" + a + ")");
      System.out.println("stack: " + st);
   }

   static void showpop(Stack st) {
      System.out.print("pop -> ");
      Integer a = (Integer) st.pop();
      System.out.println(a);
      System.out.println("stack: " + st);
   }

   public static void main(String args[]) {
      Stack st = new Stack();
      System.out.println("stack: " + st);
      showpush(st, 42);
      showpush(st, 66);
      showpush(st, 99);
      showpop(st);
      showpop(st);
      showpop(st);
      try {
         showpop(st);
      } catch (EmptyStackException e) {
         System.out.println("empty stack");
      }
   }
}

This will produce the following result −

Output

stack: [ ]
push(42)
stack: [42]
push(66)
stack: [42, 66]
push(99)
stack: [42, 66, 99]
pop -> 99
stack: [42, 66]
pop -> 66
stack: [42]
pop -> 42
stack: [ ]
pop -> empty stack

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Java – Stack