Stack

public class App {
     public static void main(String[] args) {

        Stack theStack = new Stack(5);
////
//        theStack.push('h');  //0
//        theStack.push('e');  //1
//        theStack.push('l');  //2
//        theStack.push('l');  //3
//        theStack.push('o');  //4
//
//        while (!theStack.isEmpty()) {
//            char value = theStack.pop();
//            System.out.print(value);
//        }
        String input = "hola como estas hello how are you";

        System.out.println(reverseString(input));
    }


    public static String reverseString(String str){
        int stackSize = str.length(); // get the max stack size
        Stack theStack = new Stack(stackSize); // we make the stack
        for(int j = 0; j < str.length(); j++){
            char ch = str.charAt(j); // getting a char from the input string
            theStack.push(ch);
        }

        String result = "";
        while(!theStack.isEmpty()){
            char ch = theStack.pop();
            result = result+ ch; // appending to the output
        }

        return result;
    }

}




    public static class Stack {
        private final int maxSize;
        private final char[] stackArray;
        private int top;

        public Stack(int size) {
            this.maxSize = size;

            this.stackArray = new char[maxSize];
            this.top = -1;
        }

        public void push(char j) {                       // top=0                     top=1                    top=2           top=3
            if (isFull())
                System.out.println("stack is full");
            else
                top++;
            stackArray[top] = j;
            // stackArray[0]=20;      stackArray[1]=40        stackArray[2]=60       stackArray[3]=80
        }


        public char pop() {

            if (isEmpty()) {
                System.out.println("stack is empty");
                return '0';
            } else {
                int old_top = top;                                  //top=3

                top--;
                return stackArray[old_top];                         // return 3     80 60  40 20

            }                                                           //top=2
        }

        public char peak() {
            return stackArray[top];
        }

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

        }

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

}