Question

import java.util.Iterator;
import java.util.Stack;

public class StackExample {

    public static void main(String args[]){

        Stack<String> sk = new Stack<String>();

        sk.push("Hello");
        sk.push("Hello1");
        sk.push("Hello2");
        sk.push("Hello3");

        System.out.println("The Values of Stack" +sk);

        Iterator it=sk.iterator();

        System.out.println("Size before pop() :"+sk.size());

        while(it.hasNext())
        {
            String iValue=(String)it.next();
            System.out.println("Iterator value :"+iValue);
        }

        String value =(String)sk.pop();

        System.out.println("value :"+value);

        System.out.println("Size After pop() :"+sk.size());



    }

}

Can anyone explain me the below questions.

while(it.hasNext()){
            String iValue=(String)it.next();
            System.out.println("Iterator value :"+iValue);
}

1. Why do we iterate in this manner and what does the hasNext and next
   do? Can i not do the same with an for loop.

   String value =(String)sk.pop();
   

2. What does the (String)sk.pop means… why does it not compile when i
   remove the (String)

3. Can anyone lead me to some good and complex Stack examples in Java

Answer 1

1. Why do we iterate in this manner and what does the hasNext and next do? Can i not do the same with an for loop.

The next fetches the next value from the iterator, and hasNext tells you whether or not there is a next value available.

Yes, you could do the same with a for loop:

for (String str: sk)
    System.out.println(str);

should do just as fine for instance.

2. What does the (String)sk.pop means… why does it not compile when i remove the (String)

When you pop an element of a stack, you remove the “top” (last inserted) element. The (String) part is a cast. This is neccesary if the pop returns an Object and (you know it’s actually a String) and you want to store it in a String reference.

3. Can anyone lead me to some good and complex Stack examples in Java

Complex stack examples? Uhm, no, I can’t. A stack basically provide push and pop which are really simple. Whatever the example would be, it would be complex due to something else than the use of a stack, which won’t help you understand stacks any better 🙂