Deque getFirst() method in Java
The getFirst() method of Deque Interface returns the first element or the head of the Deque. It does not deletes the element. It throws an exception when the Deque is empty.
Syntax:
E getFirst()
Parameters: This method does not accepts any parameter.
Returns: This method returns the first element or the head of the Deque but does not delete it.
Exception: The function throws NoSuchElementException when the Deque is empty and the function is called.
Below programs illustrate getFirst() method of Deque:
Program 1: With the help of LinkedList.
Java
import java.util.*;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
Deque<Integer> DQ
= new LinkedList<Integer>();
DQ.add( 7855642 );
DQ.add( 35658786 );
DQ.add( 5278367 );
DQ.add( 74381793 );
System.out.println( "Deque: " + DQ);
System.out.println( "Deque's head: " + DQ.getFirst());
}
}
|
Output:
Deque: [7855642, 35658786, 5278367, 74381793]
Deque's head: 7855642
Program 2: With the help of ArrayDeque.
Java
import java.util.*;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
Deque<Integer> DQ
= new ArrayDeque<Integer>();
DQ.add( 7855642 );
DQ.add( 35658786 );
DQ.add( 5278367 );
DQ.add( 74381793 );
System.out.println( "Deque: " + DQ);
System.out.println( "Deque's head: " + DQ.getFirst());
}
}
|
Output:
Deque: [7855642, 35658786, 5278367, 74381793]
Deque's head: 7855642
Program 3: With the help of LinkedBlockingDeque.
Java
import java.util.*;
import java.util.concurrent.LinkedBlockingDeque;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
Deque<Integer> DQ
= new LinkedBlockingDeque<Integer>();
DQ.add( 7855642 );
DQ.add( 35658786 );
DQ.add( 5278367 );
DQ.add( 74381793 );
System.out.println( "Deque: " + DQ);
System.out.println( "Deque's head: " + DQ.getFirst());
}
}
|
Output:
Deque: [7855642, 35658786, 5278367, 74381793]
Deque's head: 7855642
Program 4: With the help of ConcurrentLinkedDeque.
Java
import java.util.*;
import java.util.concurrent.ConcurrentLinkedDeque;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
Deque<Integer> DQ
= new ConcurrentLinkedDeque<Integer>();
DQ.add( 7855642 );
DQ.add( 35658786 );
DQ.add( 5278367 );
DQ.add( 74381793 );
System.out.println( "Deque: " + DQ);
System.out.println( "Deque's head: " + DQ.getFirst());
}
}
|
Output:
Deque: [7855642, 35658786, 5278367, 74381793]
Deque's head: 7855642
Program 2:
Java
import java.util.*;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
Deque<Integer> DQ
= new LinkedList<Integer>();
DQ.add( 7855642 );
DQ.add( 35658786 );
DQ.add( 5278367 );
DQ.add( 74381793 );
System.out.println( "Deque: " + DQ);
System.out.println( "Deque's head: " + DQ.getFirst());
DQ.clear();
System.out.println( "Deque's head: " + DQ.getFirst());
}
}
|
Output:
Exception in thread "main" java.util.NoSuchElementException
at java.util.LinkedList.getFirst(LinkedList.java:244)
at GFG.main(GFG.java:29)
Last Updated :
19 Sep, 2023
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