This is a simple Java program to demonstrate the Stack data structure implementation. This code provides a simple implementation of a stack with basic operations (push, pop, and isEmpty). Understanding how a stack works is fundamental, and this code demonstrates the concept in a straightforward manner. Additionally, it introduces the concept of an inner class (Node), which is commonly used in data structure implementations. Internally, the stack is implemented as a linked list.
push Method:
- The
pushmethod is used to add a new item to the top of the stack. - It creates a new node (
newTop) and assigns the valueNto itsitemfield. - The
nextfield of the new node is set to the current top of the stack. - Finally, the
topreference is updated to the new node.
pop Method:
- The
popmethod removes the top item from the stack and returns its value. - It first retrieves the value of the top item (
topItem), updates thetopreference to the next node in the stack, and then returns the retrieved value. - Note: This method does not handle the case where an attempt is made to pop from an empty stack. It would be better to throw a specific exception in that case.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 | public class NumberStack { private static class Node { // An object of type Node holds one of the // items on the stack; double item; Node next; } // Pointer to the Node that is at the top of // of the stack. If top == null, then the // stack is empty. private Node top; // Add N to the top of the stack. public void push( double N ) { Node newTop = new Node(); newTop.item = N; newTop.next = top; top = newTop; } // Remove the top item from the stack, and return it. // Note that this routine will throw a NullPointerException // if an attempty is made to pop an item from an empty // stack. (It would be better style to define a new // type of Exception to throw in this case.) public double pop() { double topItem = top.item; top = top.next; return topItem; } // Returns true if the stack is empty. Returns false // if there are one or more items on the stack. public boolean isEmpty() { return top == null; } } |
