CODEWITHSUNDEEP
javalinked-list
user2031271
user2031271

Reputation:

What is the difference between getFirst() and peekFirst() in Java's LinkedList?

In Java's LinkedList implementation, I see two methods which seems to me like having identical functions.

getFirst() --Returns the first element in this list.

peekFirst() --Retrieves, but does not remove, the first element of this list, or returns null if this list is empty.

Both of them get the pointer to the First element in the LinkedList without making any changes to it. Then, what's the difference ?

The only difference I see is that peekFirst returns null if the list is empty and getFirst throws a NoSuchElementException if the list is empty. What was the use of such a design pattern ?

Upvotes: 18

Views: 12899

Answers (4)

Shraboni Sinha
Shraboni Sinha

Reputation: 21

If your LinkedList has data then there is no difference, but if your LinkedList is empty then the peekFirst() method returns null. It doesn't throw any errors or exceptions but getFirst() method throws an exception if the list is empty.

Upvotes: 0

Evgeniy Dorofeev
Evgeniy Dorofeev

Reputation: 136162

LinkedList is a Deque. Deque API defines methods which exist in two forms: one throws an exception if the operation fails, the other returns a special value (either null or false, depending on the operation).

Upvotes: 3

Nitul
Nitul

Reputation: 1035

Only one reson: 1) It reduces the Exception Handling while development

 public E peekFirst() {
     if (size==0)
        return null;

     return getFirst();
 }

Above is the implementation of peekFirst(), it just check the size ZERO, and returns NULL instead of throwing Exception

Upvotes: 8

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 727137

Java introduced LinkedList in version 1.2. This is when the getFirst method has been provided. This message threw NoSuchElementException when the list is empty, causing programmers to do an extra check before the call:

Element e = null;
if (!myList.isEmpty()) {
     e = myList.getFirst();
}

This was an inconvenience, which has been fixed in Java version 1.6 by adding the peekFirst method and other methods of the Dequeue<T> interface.

Upvotes: 20

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