I agree with the previous answers that a Singleton is a good example of a class having a private constructor. I would though recommend a different implementation: a thread safe Singleton:
/**
* Thread safe singleton
*/
public class Singleton {
private static volatile Singleton instance = null;
/**
* Private constructor
*/
private Singleton() {
}
/**
* Gets the Instance of the Singleton in a thread safe way.
* @return
*/
public static Singleton getInstance() {
if (instance == null) {
synchronized (Singleton.class) {
if (instance == null) {
instance = new Singleton();
}
}
}
return instance;
}
}
Using a singleton in a thread safe way will safe you a lot of pain in parallel code.
