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The addFirst(E e) method of BlockingDeque inserts the element passed in the parameter to the front of the Deque if there is space. If the BlockingDeque is capacity restricted and no space is left for insertion, it returns an IllegalStateException. Syntax:

public void addFirst(E e)

Parameters: This method accepts a mandatory parameter e which is the element to be inserted in the front of the BlockingDeque. Returns: This method does not returns anything. Exception:

IllegalStateException: if the element cannot be added at this time due to capacity restrictions
NullPointerException: if the specified element is null

Note: The addFirst() method of BlockingDeque has been inherited from the LinkedBlockingDeque class in Java. Below programs illustrate addFirst() method of BlockingQueue: Program 1:

Java

// Java Program Demonstrate addFirst()
// method of BlockingDeque

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of BlockingDeque
        BlockingDeque<Integer> BD
            = new LinkedBlockingDeque<Integer>();

        // Add numbers to front of BlockingDeque
        BD.addFirst(7855642);
        BD.addFirst(35658786);
        BD.addFirst(5278367);
        BD.addFirst(74381793);

        // before removing print Dequq
        System.out.println("Blocking Deque: " + BD);
    }
}

Output:

Blocking Deque: [74381793, 5278367, 35658786, 7855642]

Program 2:

Java

// Java Program Demonstrate addFirst()
// method of BlockingDeque
// when it is Full
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of BlockingDeque
        // size of list
        BlockingDeque<Integer> BD
            = new LinkedBlockingDeque<Integer>(3);

        // Add numbers to front of BlockingDeque
        BD.addFirst(7855642);
        BD.addFirst(35658786);
        BD.addFirst(5278367);

        // it is full
        BD.addFirst(74381793);

        // before removing print Deque
        System.out.println("Blocking Deque: " + BD);
    }
}

Output:

Exception in thread "main" java.lang.IllegalStateException: Deque full
    at java.util.concurrent.LinkedBlockingDeque.addFirst(LinkedBlockingDeque.java:326)
    at GFG.main(GFG.java:24)

Program 3:

Java

// Java Program Demonstrate addFirst()
// method of BlockingDeque
// when nill is inserted

import java.util.concurrent.BlockingDeque;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of BlockingDeque
        BlockingDeque<Integer> BD
            = new LinkedBlockingDeque<Integer>();

        // Add numbers to front of BlockingDeque
        BD.addFirst(7855642);
        BD.addFirst(35658786);
        BD.addFirst(5278367);

        // NULL
        BD.addFirst(null);

        // before removing print Deque
        System.out.println("Blocking Deque: " + BD);
    }
}

Output:

Exception in thread "main" java.lang.NullPointerException
    at java.util.concurrent.LinkedBlockingDeque.offerFirst(LinkedBlockingDeque.java:342)
    at java.util.concurrent.LinkedBlockingDeque.addFirst(LinkedBlockingDeque.java:325)
    at GFG.main(GFG.java:24)

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingDeque.html#addFirst(E)

BlockingDeque addFirst() method in Java with Examples

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