Stack of Strings Implemented in Java

In my previous post we talked about stack implementation using character array.

In this post I will be sharing my code for a stack implementation which can hold String values in other words stack implemented using array of String in java.

Sections in this post: 

1. String Array Based Implementation of stack.

 Let see the code directly as it is self explanatory

public class StackOfStrings {
 // Every stack has a maximum capacity i.e. number of objects it can hold, 
 private static final int CAPACITY = 10;
 // Top will always point to most recently added element in stack 
 //therefore top = -1 implies stack is empty 
 private int top = -1;
 //array to hold stack elemnts.lt is initialized to capacity of stack
 private String[] stackArray = new String[CAPACITY];

 public static void main(String[] args) {
  StackOfStrings stack = new StackOfStrings();
  stack.pop();
  stack.push("aa");
  stack.push("bb");
  stack.push("cc");
  stack.push("dd");
  stack.push("ee");
  stack.printStack();
  System.out.println("=============================");
  System.out.println(stack.pop());
  System.out.println(stack.pop());
  System.out.println(stack.pop());
  System.out.println(stack.pop());
  System.out.println(stack.pop());
  System.out.println(stack.pop());
  System.out.println(stack.pop());
 }

 public boolean isEmpty() {
  return top == -1;
 } 

 public boolean push(String data) {
  
   // Check if stack is full
   // If it is full then we show Stack overflow message
   
  if (isFull()) {
   System.out.println("Stack overflow");
   return false;
  } else {
   stackArray[++top] = data;
   return true;
  }
 }

 public String pop() {
  
   // Check if stack is empty
   //  If it is empty then we show Stack underflow message
   
  if (isEmpty()) {
   System.out.println("Stack underflow");
  } else {
   // decrementing top by one to sake second element from top as top
   top--;
   // we will be returning top+1 value from array 
   //as we have already made top to point second element in stack
   return stackArray[top + 1];
  }
  return null;
 }

 public String peek() {
  // we implement peek by first popping top element then pushing it back
  String element = null;
  if (!isEmpty()) {
   element = pop();
   push(element);
  }
  return element;
 } 

 public boolean isFull() {
  return top == CAPACITY - 1;
 }

 
  // this method just gives view of the stack.
  // As there are only two operation for stack 
  // i.e. push and pop so in theory we can never print a stack
  // without calling those two methods
  
 public void printStack() {
  System.out.print("[");
  for (int i = top; i >= 0; i--) {
   System.out.print(" " + stackArray[i]);
  }
  System.out.println(" ]");
 } 
}

 If we run the program we will get output like this:

Output

================================================================================

Stack underflow
[    ee    dd    cc    bb    aa    ]
=============================
ee
dd
cc
bb
aa
Stack underflow
null
Stack underflow
null

 

Please share your comments if you find anything incorrect, or you want to share more information about the topic discussed above.

 

For further reading:

practice questions on stack

Stack Implementation using int array

Stack Implementation using char array

Stack implementation using link list 

Stack implementation by link list node, 

Stack implementation using doubly link list 

Stack implementation by doubly link list node . 

For complete listing see data structure and algorithm page