java tip of the day - explicitly set unused (or no longer used) variables/objects/references to null to make them available for garbage collection

especially in large java programs, it's important to explicitly set unused (or no longer used) variables/objects/references to null to make them available for garbage collection.

Here is an example of "nulling the reference":

public class GarbageCollectionExample {

    public static void main(String[] args) {
        StringBuffer x = new StringBuffer("test");
        System.out.println(x);
        // the StringBuffer "test" is not available for GC yet
        x = null;
        // the StringBuffer "test" is now available for GC
    }
}

Here is an example of "reassigning a reference value":

public class GarbageCollectionExample {

    public static void main(String[] args) {
        StringBuffer x = new StringBuffer("test");
        StringBuffer y = new StringBuffer("asdf");
        System.out.println(x);
        // the StringBuffer "test" is not available for GC yet
        x = y;
        // the StringBuffer "test" is now available for GC}

the StringBuffer "test" is no longer reachable because "x" now references the StringBuffer "asdf".


(taken from pages 257-258 in "Sun Certified Programmer for Java 6 Study Guide")