Java: getInstance vs Static

Question

What is the purpose of getInstance() in Java?

During my research I keep reading that getInstance() helps achieve a Singleton design pattern (w

Answer 1

One overlooked reason to use a singleton instead of static class member variables is that the static member variables MAY use space and garbage collector time even in the event the class is never instantiated. Consider how many classes are available to you in rt.jar and what a small fraction of them you probably use in any given application. Also consider that using getInstance ensures your "constructor" has run before any of the member variables are accessed. I almost universally see getInstance as synchronized but I feel this is a bad idea. If anyone ever adds a synchronized blocking method calls to Singleton.getInstance().unsynchronized() could be needlessly held up.

private static Singleton instance = null;
private Singleton() {}
public final static Singleton getInstance() {
    return (instance != null) ? instance : makeInstance();
}
private final static synchronized Singleton makeInstance() {
    return ( instance != null ) ? instance : ( instance = new Singleton() );
}