BlockingDeque takeFirst() method in Java with Examples

The takeFirst() method of BlockingDeque returns and removes the first element of the Deque container from it, waiting if necessary until an element becomes available.. The method throws an InterruptedException if it is interrupted while waiting.

Syntax:

public E takeFirst()

Returns: This method returns the first element of the Deque container, waiting if necessary until an element becomes available.

Exception: The function throws an InterruptedException if it is interrupted while waiting.

Note: The takeFirst() method of BlockingDeque has been inherited from the LinkedBlockingDeque class in Java.

Below programs illustrate takeFirst() method of LinkedBlockingDeque:

Program 1:

// Java Program to demonstrate takeFirst()
// method of BlockingDeque

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

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

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

        // Add numbers to end of BlockingDeque
        BD.add(7855642);
        BD.add(35658786);
        BD.add(5278367);
        BD.add(74381793);

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

        // removes the front element and prints it
        System.out.println("Head of Blocking Deque: "
                           + BD.takeFirst());

        // prints the Deque
        System.out.println("Blocking Deque: " + BD);
    }
}

Output:

Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Head of Linked Deque: 7855642
Blocking Deque: [35658786, 5278367, 74381793]

Program 2: To demonstrate InterruptedException

// Java Program to demonstrate takeFirst()
// 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 InterruptedException
    {

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

        // Add numbers to end of BlockingDeque
        BD.add(7855642);
        BD.add(35658786);
        BD.add(5278367);
        BD.add(74381793);

        // print Dequeue
        System.out.println("Blocking Deque: " + BD);

        BD.clear();

        // throws error as the list is empty and it
        // is interrupted while waiting
        System.out.println("Head of Blocking Deque: "
                           + BD.takeFirst());
    }
}

Runtime Errors:

Max real time limit exceeded due to either by heavy load on server or by using sleep function

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