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Java - Queue element() Method
Description
The Java Queue element() retrieves, but does not remove, the head of this queue. This method differs from peek only in that it throws an exception if this queue is empty.
Declaration
Following is the declaration for java.util.Queue.element method
public E element()
Parameters
NA
Return Value
This method returns the head of the list represented by this queue.
Exception
NoSuchElementException − if the queue is empty.
Example 1
The following example shows the usage of Java Queue element() method with Integers. We're creating an LinkedList of Integers, adding some elements, print it and then use element() method to get the first element. Queue remains untouched.
package com.tutorialspoint; import java.util.LinkedList; import java.util.Queue; public class QueueDemo { public static void main(String[] args) { // create an empty queue Queue<Integer> queue = new LinkedList<>(); // use add() method to add elements in the queue queue.add(25); queue.add(30); queue.add(20); queue.add(18); // let us print all the elements available in queue System.out.println("Queue = " + queue); // it will retrieve element at first(head) position System.out.println("Retrieved Element is = " + queue.element()); // let us print all the elements available in queue again System.out.println("Queue = " + queue); } }
Output
Let us compile and run the above program, this will produce the following result −
Queue = [25, 30, 20, 18] Retrieved Element is = 25 Queue = [25, 30, 20, 18]
Example 2
The following example shows the usage of Java Queue element() method with Strings. We're creating an LinkedList of Strings, adding some elements, print it and then use element() method to get the first element. Queue remains untouched.
package com.tutorialspoint; import java.util.LinkedList; import java.util.Queue; public class QueueDemo { public static void main(String[] args) { // create an empty queue Queue<String> queue = new LinkedList<>(); // use add() method to add elements in the queue queue.add("A"); queue.add("B"); queue.add("C"); queue.add("D"); // let us print all the elements available in queue System.out.println("Queue = " + queue); // it will retrieve element at first(head) position System.out.println("Retrieved Element is = " + queue.element()); // let us print all the elements available in queue again System.out.println("Queue = " + queue); } }
Output
Let us compile and run the above program, this will produce the following result −
Queue = [A, B, C, D] Retrieved Element is = A Queue = [A, B, C, D]
Example 3
The following example shows the usage of Java Queue element() method with Student objects. We're creating an LinkedList of Student objects, adding some students, print it and then use element() method to get the first student. Queue remains untouched.
package com.tutorialspoint; import java.util.LinkedList; import java.util.Queue; public class QueueDemo { public static void main(String[] args) { // create an empty queue Queue<Student> queue = new LinkedList<>(); // use add() method to add elements in the queue queue.add(new Student(1, "Julie")); queue.add(new Student(2, "Robert")); queue.add(new Student(3, "Adam")); // let us print all the elements available in queue System.out.println("Queue = " + queue); // it will retrieve element at first(head) position System.out.println("Retrieved Element is = " + queue.element()); // let us print all the elements available in queue again System.out.println("Queue = " + queue); } } 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 −
Queue = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]] Retrieved Element is = [ 1, Julie ] Queue = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]
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