SatyaCodes

Java- Stack

Stack– Internal implementation

The Stack class represents a last-in-first-out (LIFO) stack of objects. It extends class Vector with five operations(below 5 methods) that allow a vector to be treated as a stack

Object push(Object o) -Insert an object into top of the stack

Object pop() -Removes & returns from top of the stack

Object peak() -Just returns Object from top of the stack

boolean empty() -returns TRUE if stack is empty

int search(Object o) – returns offset if available otherwise -1

  • Adding item in Stack is called PUSH.

  • Removing item from stack is called POP.

  • Push and pop operations happen at Top of stack.

  • Stack follows LIFO (Last in first out) - means last added element is removed first from stack

  • Push - O(1) [as we push element at Top of Stack in java]

  • Pop - O(1) [as popping is also done at Top of Stack in java]

Uses Growable array, initial capacity as 10, same as ArrayList

public class StackDemo {
    public static void main(String[] args) {
        Stack s = new Stack();
        s.push("A");
        s.push("B");
        s.push("C");
        System.out.println(s);// [A, B, C]

        System.out.println(s.search("A"));// 3
        System.out.println(s.search("X"));// -1
        
        s.pop();
        System.out.println(s);//[A, B]
    }
}
[A, B, C]
3
-1


Cursors - Enumeration VS Iterator VS ListIterator

ListIterator is subclass of List.so all the methods are available in ListIterator.

We have to follow 3 steps to use Cursors in our application

  1. Get the all elements in a collection in Cursor Object

  2. Check is next/previous element is exist or not

  3. Get the element

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