Java - Queue add() Method

Description

The Java Queue add(E e) method inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.

Declaration

Following is the declaration for java.util.Queue.add() method

public boolean add(E e)

Parameters

e − The element to be appended to this list.

Return Value

This method returns true.

Exception

IllegalStateException − if the element cannot be added at this time due to capacity restrictions

ClassCastException − if the class of the specified element prevents it from being added to this queue

NullPointerException − if the specified element is null and this queue does not permit null elements

IllegalArgumentException − if some property of this element prevents it from being added to this queue

Example 1

The following example shows the usage of Java Queue add(E) method to add Integers. We're adding couple of Integers to the LinkedList object using add() method calls per element and then print each element to show the elements added.

package com.tutorialspoint;

import java.util.LinkedList;
import java.util.Queue;

public class QueueDemo {
   public static void main(String[] args) {
      
      // create an empty queue
      Queue<Integer> queue = new LinkedList<>();

      // use add() method to add elements in the queue
      queue.add(20);
      queue.add(30);
      queue.add(20);
      queue.add(30);
      queue.add(15);
      queue.add(22);
      queue.add(11);

      // let us print all the elements available in queue
      for (Integer number : queue) {
         System.out.println("Number = " + number);
      }
   }
}

Output

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

Number = 20
Number = 30
Number = 20
Number = 30
Number = 15
Number = 22
Number = 11

Example 2

The following example shows the usage of Java Queue add(E) method to add Strings. We're adding couple of strings to the LinkedList object using add() method calls per element and then printing the Queue using its toString() method.

package com.tutorialspoint;

import java.util.LinkedList;
import java.util.Queue;

public class QueueDemo {
   public static void main(String[] args) {
      
      // create an empty queue
      Queue<String> queue = new LinkedList<>();

      // use add() method to add elements in the queue
      queue.add("Welcome");
      queue.add("To");
      queue.add("Tutorialspoint");
      System.out.println("Queue = " + queue);      
   }
}

Output

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

Queue = [Welcome, To, Tutorialspoint]

Example 3

The following example shows the usage of Java Queue add(index, E) method to add Student objects at particular index. We're adding couple of Student objects to the LinkedList object using add() method calls per element and using add(index, E) in the end to add a student at particular location and then printing the LinkedList using its toString() method.

package com.tutorialspoint;

import java.util.LinkedList;
import java.util.Queue;

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

      // create an empty queue
      Queue<Student> queue = new LinkedList<>();

      // use add() method to add elements in the queue
      queue.add(new Student(1, "Julie"));
      queue.add(new Student(2, "Robert"));
      System.out.println("Queue = " + queue);      
   }
}

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 + " ]";
   }
}

Output

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

Queue = [[ 1, Julie ], [ 2, Robert ]]