CODEWITHSUNDEEP
javalinked-list
user2698544
user2698544

Reputation: 59

linked list deletion in java

How do I delete a linked list completely in java. Some tutorials are suggesting that I should delete it node by node . But if I make head to null simply, would it be wrong ? As all the elements would be eligible for garbage collection.

Upvotes: 0

Views: 1021

Answers (3)

Ram Patra
Ram Patra

Reputation: 16664

Yes, you can simply assign the head as null but to be on the safe side (as in if some nodes are being referred from elsewhere) it is better to make all nodes null.

If you look at the code in java.util.LinkedList, the clear() method does the same.

/**
 * Removes all of the elements from this list.
 * The list will be empty after this call returns.
 */
public void clear() {
    // Clearing all of the links between nodes is "unnecessary", but:
    // - helps a generational GC if the discarded nodes inhabit
    //   more than one generation
    // - is sure to free memory even if there is a reachable Iterator
    for (Node<E> x = first; x != null; ) {
        Node<E> next = x.next;
        x.item = null;
        x.next = null;
        x.prev = null;
        x = next;
    }
    first = last = null;
    size = 0;
    modCount++;
}

first reference is head in your case.

You can also refer to this comprehensive answer.

Upvotes: 0

AnkeyNigam
AnkeyNigam

Reputation: 2820

You can point the LinkedList reference variable to null.

Any reference variable referring to null is automatically eligible for Garbage Collection

List list = new LinkedList();
list.add("hi");
list = null; // now eligible for *Garbage Collection*, leave it for JVM to handle

Moreover if you do list.clear() it will clear all the elements inside this list but not the list itself.

Also we can call System.gc() but System.gc() will not ensure that Garbage Collector will run for sure, it can only asks the JVM to run the GC , but is totally dependent on JVM, so we should levae it to JVM only to handle GC.

For more info see this Oracle Doc here

Upvotes: 0

Bathsheba
Bathsheba

Reputation: 234635

You can't. You can only recommend the list as a candidate for garbage collection by removing all references to it.

If you own the only reference then setting that reference to null will schedule the object for garbage collection. You can advise a garbage collection using System.gc() but that's not particularly good style and not all JVMs support it.

Removing the elements node by node (use clear()) can help a little since it will reduce the number of references held on each of the list items. That will reduce the amount of memory that the list consumes.

Upvotes: 2

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