Java - Deque size() Method

The Java Deque size() method returns the number of elements in this deque. It is updated everytime a change is made to the Deque.

Declaration

Following is the declaration for java.util.Deque.size() method

public int size()

Parameters

NA

Return Value

This method returns the number of elements in this deque.

Exception

NA

Example 1

The following example shows the usage of Java Deque size() method with Integers. We're creating an Deque of Integers, adding some elements, print the size and then use remove() method to remove the first element. As Deque is modified its size is printed again.

package com.tutorialspoint;

import java.util.ArrayDeque;
import java.util.Deque;

public class DequeDemo {
   public static void main(String[] args) {
      
      // create an empty array deque
      Deque<Integer> deque = new ArrayDeque<>();

      // use add() method to add elements in the deque
      deque.add(25);
      deque.add(30);
      deque.add(20);
      deque.add(18);        

      // let us print the size of deque
      System.out.println("Size of Deque = " + deque.size());

      // it will retrieve first element after removing from deque
      deque.remove();
	  
      // let us print the size of deque again
      System.out.println("Size of Deque = " + deque.size());
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Size of Deque = 4
Size of Deque = 3

Example 2

The following example shows the usage of Java Deque size() method with Strings. We're creating an Deque of Strings, adding some elements, print the size and then use remove() method to remove the first element. As Deque is modified its size is printed again.

package com.tutorialspoint;

import java.util.ArrayDeque;
import java.util.Deque;

public class DequeDemo {
   public static void main(String[] args) {
      
      // create an empty array deque
      Deque<String> deque = new ArrayDeque<>();

      // use add() method to add elements in the deque
      deque.add("A");
      deque.add("B");
      deque.add("C");
      deque.add("D");        

      // let us print the size of deque
      System.out.println("Size of Deque = " + deque.size());

      // it will retrieve first element after removing from deque
      deque.remove();
	  
      // let us print the size of deque again
      System.out.println("Size of Deque = " + deque.size());
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Size of Deque = 4
Size of Deque = 3

Example 3

The following example shows the usage of Java Deque size() method with Student objects. We're creating an Deque of Student objects, adding some elements, print the size and then use remove() method to remove the first element. As Deque is modified its size is printed again.

package com.tutorialspoint;

import java.util.ArrayDeque;
import java.util.Deque;

public class DequeDemo {
   public static void main(String[] args) {
      
      // create an empty array deque
      Deque<Student> deque = new ArrayDeque<>();

      // use add() method to add elements in the deque
      deque.add(new Student(1, "Julie"));
      deque.add(new Student(2, "Robert"));
      deque.add(new Student(3, "Adam"));       

      // let us print the size of deque
      System.out.println("Size of Deque = " + deque.size());

      // it will retrieve first element after removing from deque
      deque.remove();
	  
      // let us print the size of deque again
      System.out.println("Size of Deque = " + deque.size());
   }
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
   
   @Override
   public boolean equals(Object obj) {
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Size of Deque = 3
Size of Deque = 2