Java ArrayDeque getFirst() Method

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Description

The Java ArrayDeque getFirst() method retrieves, but does not remove, the first element of this deque. So we can get the first element without modifying the ArrayDeque object.

Declaration

Following is the declaration for Java ArrayDeque getFirst() method

public E getFirst()

Parameters

NA

Return Value

This method returns the head of this deque.

Exception

NoSuchElementException − if this deque is empty.

Getting First Element of an ArrayDeque of Integers Example

The following example shows the usage of Java ArrayDeque getFirst() method with Integers. We're creating an ArrayDeque of Integers, adding some elements, print it and then use getFirst() method to get the first element. ArrayDeque remains untouched.

package com.tutorialspoint;

import java.util.ArrayDeque;

public class ArrayDequeDemo {
   public static void main(String[] args) {
      
      // create an empty array deque
      ArrayDeque<Integer> deque = new ArrayDeque<>();

      // use add() method to add elements in the deque
      deque.add(25);
      deque.add(30);
      deque.add(20);
      deque.add(18);        

      // let us print all the elements available in deque
      System.out.println("ArrayDeque = " + deque);

      // it will retrieve first element
      System.out.println("Retrieved Element is = " + deque.getFirst());
	  
      // let us print all the elements available in deque again
      System.out.println("ArrayDeque = " + deque);
   }
}

Output

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

ArrayDeque = [25, 30, 20, 18]
Retrieved Element is = 25
ArrayDeque = [25, 30, 20, 18]

Getting First Element of an ArrayDeque of Strings Example

The following example shows the usage of Java ArrayDeque getFirst() method with Strings. We're creating an ArrayDeque of Strings, adding some elements, print it and then use getFirst() method to get the first element. ArrayDeque remains untouched.

package com.tutorialspoint;

import java.util.ArrayDeque;

public class ArrayDequeDemo {
   public static void main(String[] args) {
      
      // create an empty array deque
      ArrayDeque<String> deque = new ArrayDeque<>();

      // use add() method to add elements in the deque
      deque.add("A");
      deque.add("B");
      deque.add("C");
      deque.add("D");        

      // let us print all the elements available in deque
      System.out.println("ArrayDeque = " + deque);

      // it will retrieve first element
      System.out.println("Retrieved Element is = " + deque.getFirst());
	  
      // let us print all the elements available in deque again
      System.out.println("ArrayDeque = " + deque);
   }
}

Output

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

ArrayDeque = [A, B, C, D]
Retrieved Element is = A
ArrayDeque = [A, B, C, D]

Getting First Element of an ArrayDeque of Objects Example

The following example shows the usage of Java ArrayDeque getFirst() method with Student objects. We're creating an ArrayDeque of Student objects, adding some students, print it and then use getFirst() method to get the first student. ArrayDeque remains untouched.

package com.tutorialspoint;

import java.util.ArrayDeque;

public class ArrayDequeDemo {
   public static void main(String[] args) {
      
      // create an empty array deque
      ArrayDeque<Student> deque = new ArrayDeque<>();

      // use add() method to add elements in the deque
      deque.add(new Student(1, "Julie"));
      deque.add(new Student(2, "Robert"));
      deque.add(new Student(3, "Adam"));       

      // let us print all the elements available in deque
      System.out.println("ArrayDeque = " + deque);

      // it will retrieve first element
      System.out.println("Retrieved Element is = " + deque.getFirst());
	  
      // let us print all the elements available in deque again
      System.out.println("ArrayDeque = " + deque);
   }
}
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 + " ]";
   }
   
   @Override
   public boolean equals(Object obj) {
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
}

Output

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

ArrayDeque = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]
Retrieved Element is = [ 1, Julie ]
ArrayDeque = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]