Java Stack class with examples

1. Java Stack class

In Java Stack class is a child class of Vector class in collection framework.

A Stack class represents a last-in-first-out (LIFO) stack of objects. A Stack supports two principle operations called push and pop .

2. Java Stack data structure :

The Stack class data structure is Last-In-First-Out (LIFO). Below Image illustrates java Stack data structure.

3. When do we use Stack in Java? 

A Stack is ideal fit to use whenever last in first out (LIFO) order required. But java documentation recommend for more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations like ArrayDeque, which should be used in preference to this class. A Deque is double ended queue, it allows both LIFO and FIFO.

All the Stack methods are Synchronized, if Synchronization needed and LIFO order required you can go for Stack, otherwise it’s advised to use ArrayDeque .

4. Class Hierarchy of Java Stack :

5. Stack class methods and examples

Following are the Stack class methods, However as Stack extends Vector class, by inheritance we can use Collection, List, Vector methods also using stack instance.

1. Object push(Object element) : push() method use to push an item onto the top of the stack.
2. Object pop() : pop() method use to remove the object at the top of the stack and returns that object as the value.
3. Object peek() : peek() method use to looks at the object at the top of this stack without removing it from the stack.
4. boolean empty() : It returns true if nothing is on the top of the stack. Else, returns false.
5. int search(Object element) : search() method returns position of the element if element is exist, otherwise returns -1. This method can used to determine an element in the stack exist or not.

5.1. Add elements to Stack example

public class JavaStackAddEelemntsDemo {

	public static void main(String[] args) {
		
        Stack<String> stack = new Stack<>();
		
        // adding elements to Stack, using stack push() method
        stack.push("Peter");
        stack.push("Martin");
        
        // adding elements to Stack, using List and Vector, Collection methods
        stack.add("Alex");
        stack.add(3, "Vijay");
        stack.addElement("Mike");
		
        System.out.println("Stack => " + stack);
	}
}

Output :

Stack => [Peter, Martin, Alex, Vijay, Mike]

5.2. Remove elements from Stack example

public class RemoveElementsFromStackDemo {

	public static void main(String[] args) {
		
        Stack<String> stack = new Stack<>();
		
        stack.push("Peter");
        stack.push("Martin");
        stack.push("Mike");
        stack.push("John");
        stack.push("Anand");
        stack.push("Alex");
        stack.push("Natarajan");
        stack.push("Gerhard");
        stack.push("Stefen");
		
        //Stack.pop() - last-in-first out, and removes top
        System.out.println("Stack.pop()1 => " + stack.pop());
        System.out.println("Stack.pop()2 => " + stack.pop());
        
        stack.remove(1);// by index
        stack.removeElement("Mike");
        stack.removeIf(name -> name.contains("G"));
        System.out.println(stack); 
	}
}

Output :

Stack.pop()1 => Stefen
Stack.pop()2 => Gerhard
[Peter, John, Anand, Alex, Natarajan]

5.3. Retrieve elements from Stack example

public class GetElementsFromStackDemo {

	public static void main(String[] args) {
		
        Stack<String> stack = new Stack<>();
		
        //Adding elements to Stack
        stack.push("Peter");
        stack.push("Martin");
        stack.push("Mike");
        stack.push("John");
        stack.push("Anand");
		
        //Stack.peek() - last-in-first out
        System.out.println("Stack.peek()1 => " + stack.peek());
        System.out.println("Stack.peek()2 => " + stack.peek());
        System.out.println(stack.get(1));// by index
        System.out.println(stack.firstElement());// by Vector method
        System.out.println(stack.lastElement());// by Vector method
        
	}
}

Output :

Stack.peek()1 => Anand
Stack.peek()2 => Anand
Martin
Peter
Anand

5.4. Search in Stack elements example

public class JavaStackSearchElementsDemo {

	public static void main(String[] args) {
		
        Stack<String> stack = new Stack<>();
		
        stack.push("Peter");
        stack.push("Martin");
        stack.push("Mike");
        stack.push("John");
        stack.push("Anand");
		
        //Stack.search() - returns position if exist, else -1
        System.out.println("Stack.search(Mike) => " + stack.search("Mike"));
        System.out.println("Stack.search(Anand) => " + stack.search("Anand"));
        System.out.println("Stack.search(Vijay) => " + stack.search("Vijay"));
	}
}

Output :

Stack.search(Mike) => 3
Stack.search(Anand) => 1
Stack.search(Vijay) => -1

5.5. Iterate or loop Stack example

public class JavaStackIterateDemo {

	public static void main(String[] args) {
		
        Stack<String> stack = new Stack<>();
		
        //Adding elements to Stack
        stack.push("Peter");
        stack.push("Martin");
        stack.push("Mike");
        stack.push("John");
        stack.push("Anand");
		
       System.out.println("------- using Enumeration --------");
       Enumeration<String> e = stack.elements();
       while(e.hasMoreElements()) {
    	   System.out.println("Person => "+e.nextElement());
       }
       
       System.out.println("------- using Stream.forEach() --------");
       stack.stream().forEach(p -> System.out.println("Person => "+p));
       
       System.out.println("------- using enhanced for-each loop --------");
       for(String s : stack)
          System.out.println("Person => "+s);
	}
}

Output :

------- using Enumeration --------
Person => Peter
Person => Martin
Person => Mike
Person => John
Person => Anand
------- using Stream.forEach() --------
Person => Peter
Person => Martin
Person => Mike
Person => John
Person => Anand
------- using enhanced for-each loop --------
Person => Peter
Person => Martin
Person => Mike
Person => John
Person => Anand

5.6. Filter Stack elements using Stream example

public class FilteringStackElementsDemo {

	public static void main(String[] args) {
		
        Stack<String> stack = new Stack<>();
		
        //Adding elements to Stack
        stack.push("Peter");
        stack.push("Martin");
        stack.push("Mike");
        stack.push("John");
        stack.push("Anand");
		
        stack.stream().
              filter(name -> name.startsWith("M")).
              forEach(p -> System.out.println("Person => "+p));
	}
}

Output :

Person => Martin
Person => Mike