I can recall when I first heard of the FizzBuzz test I laughed. I commented to a fellow worker that I cannot recall using modulus in a production system, but, as karma happens I used it three times in the next two weeks. I am having the same experience with the java modifier transient.

I was going through the Java Persistence API in particular as part of ejb3 while developing business interfaces and beans. One of the annotations in the persistence API is @Transient. This defines the property or field as non-persistent.

The transient modifier has been part of Java for a while now and describes a field as not being part of the serialisation process, either in save or restore. It turns off the persistence mechanism for that field when using serialisation.

A real world example where transient might be used is when a serializable object contains reference to a non-serializable variable. For instance in Java the Thread, Socket and ObjectOutputStream classes cannot be serialized. So to serialize an object that contains a reference to any of these then the variables have to be marked transient.

public class PersistThis implements Serializable, Runnable {
 	int counter = 0;
	transient private Thread thread;
 	public PersistThis() {
		thread = new Thread(this);
		thread.start();
	}
 	@Override
	public void run() {
		while(counter<1000) {
			System.out.println("Counter " + counter);
			counter++;			
		}		
	}
}

Note: Transient is also commonly used in session maintenance code which keeps the amount of data to bring back up after a session fallover manageable.