Queue add() method in Java

The add(E e) method of Queue Interface inserts the element passed in the parameter to the end of the queue if there is space. If the Queue is capacity restricted and no space is left for insertion, it returns an IllegalStateException. The function returns true on successful insertion.

Syntax:

boolean add(E e)

Parameters: This method accepts a mandatory parameter e which is the element to be inserted in the end of the Queue.

Returns: This method returns true on successful insertion.

Exceptions: The function throws four exceptions which are described as below:

ClassCastException: when the class of the element to be entered prevents it from being added to this container.
IllegalStateException: when the capacity of the container is full and insertion is done.
IllegalArgumentException: when some property of the element prevents it to be added to the queue.
NullPointerException: when the element to be inserted is passed as null and the Queue’s interface does not allow null elements.

Below programs illustrate add() method of Queue:

Program 1: With the help of LinkedList.

// Java Program Demonstrate add() 
// method of Queue 
  
import java.util.*; 
  
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of Queue 
        Queue<Integer> Q 
            = new LinkedList<Integer>(); 
  
        // Add numbers to end of Queue 
        Q.add(7855642); 
        Q.add(35658786); 
        Q.add(5278367); 
        Q.add(74381793); 
  
        // before removing print queue 
        System.out.println("Queue: " + Q); 
    } 
} 

Output:

Queue: [7855642, 35658786, 5278367, 74381793]

Program 2: With the help of ArrayDeque.

// Java Program Demonstrate add() 
// method of Queue 
  
import java.util.*; 
  
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of Queue 
        Queue<Integer> Q 
            = new ArrayDeque<Integer>(); 
  
        // Add numbers to end of Queue 
        Q.add(7855642); 
        Q.add(35658786); 
        Q.add(5278367); 
        Q.add(74381793); 
  
        // before removing print queue 
        System.out.println("Queue: " + Q); 
    } 
} 

Output:

Queue: [7855642, 35658786, 5278367, 74381793]

Program 3: With the help of LinkedBlockingDeque.

// Java Program Demonstrate add() 
// method of Queue 
  
import java.util.*; 
import java.util.concurrent.LinkedBlockingDeque; 
  
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of Queue 
        Queue<Integer> Q 
            = new LinkedBlockingDeque<Integer>(); 
  
        // Add numbers to end of Queue 
        Q.add(7855642); 
        Q.add(35658786); 
        Q.add(5278367); 
        Q.add(74381793); 
  
        // before removing print queue 
        System.out.println("Queue: " + Q); 
    } 
} 

Output:

Queue: [7855642, 35658786, 5278367, 74381793]

Program 4: With the help of ConcurrentLinkedDeque.

// Java Program Demonstrate add() 
// method of Queue 
  
import java.util.*; 
import java.util.concurrent.ConcurrentLinkedDeque; 
  
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of Queue 
        Queue<Integer> Q 
            = new ConcurrentLinkedDeque<Integer>(); 
  
        // Add numbers to end of Queue 
        Q.add(7855642); 
        Q.add(35658786); 
        Q.add(5278367); 
        Q.add(74381793); 
  
        // before removing print queue 
        System.out.println("Queue: " + Q); 
    } 
} 

Output:

Queue: [7855642, 35658786, 5278367, 74381793]

Below programs illustrate exceptions thrown by this method:

Program 5: To show NullPointerException.

// Java Program Demonstrate add() 
// method of Queue when Null is passed 
  
import java.util.*; 
import java.util.concurrent.LinkedBlockingQueue; 
  
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of Queue 
        Queue<Integer> Q 
            = new LinkedBlockingQueue<Integer>(); 
  
        // Add numbers to end of Queue 
        Q.add(7855642); 
        Q.add(35658786); 
        Q.add(5278367); 
  
        try { 
            // when null is inserted 
            Q.add(null); 
        } 
        catch (Exception e) { 
            System.out.println("Exception: " + e); 
        } 
    } 
} 

Output:

Exception: java.lang.NullPointerException

Program 6: To show IllegalStateException.

// Java Program Demonstrate add() 
// method of Queue when capacity is full 
import java.util.*; 
import java.util.concurrent.LinkedBlockingQueue; 
  
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of Queue 
        Queue<Integer> Q 
            = new LinkedBlockingQueue<Integer>(3); 
  
        // Add numbers to end of Queue 
        Q.add(7855642); 
        Q.add(35658786); 
        Q.add(5278367); 
  
        try { 
            // when capacity is full 
            Q.add(10); 
        } 
        catch (Exception e) { 
            System.out.println("Exception: " + e); 
        } 
    } 
} 

Output:

Exception: java.lang.IllegalStateException: Queue full

Note: The other two exceptions are internal and are caused depending on the compiler hence cannot be shown in the compiler.

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/Queue.html#add-E-

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