Peek() - It will give the head element of the queue. If queue is empty then it will return null.
Poll() - It will give the head element of the queue and will remove the head element from queue. If queue is empty then it will return null.
Remove() - It will give the head element of the queue and will remove the head element from queue. If queue is empty then it will throw an Exception.
Let's have a look at following piece of code.
import java.util.LinkedList; import java.util.Queue; public class Test { public static void main(String args[]) { Queue<Integer> queue = new LinkedList<Integer>(); queue.add(100); queue.add(200); System.out.println("Peek = " + queue.peek()); System.out.println("Queue size = " + queue.size()); System.out.println("poll = " + queue.poll()); System.out.println("Queue size = " + queue.size()); System.out.println("remove = " + queue.remove()); System.out.println("Queue size = " + queue.size()); //calling the methods on empty queue, to test the null return value and exception throw System.out.println("Peek = " + queue.peek()); System.out.println("poll = " + queue.poll()); System.out.println("remove = " + queue.remove()); } } Output: Peek = 100 Queue size = 2 poll = 100 Queue size = 1 remove = 200 Queue size = 0 Peek = null poll = null Exception in thread "main" java.util.NoSuchElementException at java.util.LinkedList.removeFirst(LinkedList.java:270) at java.util.LinkedList.remove(LinkedList.java:685) at Test.main(Test.java:24)
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