Java singleton pattern example 2016-12-17 04:51

Singleton make sure only one instance in your program. There are two kinds of singleton: initialization first, lazy initialization. The first one initializes class in the beginning. The second one initializes class when getInstance method is first invoked. The codes of them are like following.

1. Initialization first (general)

public class Singleton {
    private static Singleton singleton = new Singleton();

    public static Singleton getInstance() {
        return singleton;

    private Singleton() {

2. Lazy initialization

public class LazyInitSingleton {
    private static LazyInitSingleton lazyInitSingleton;

    private LazyInitSingleton() {

    public static synchronized LazyInitSingleton getInstance() {
        if (lazyInitSingleton == null) {
            lazyInitSingleton = new LazyInitSingleton();
        return lazyInitSingleton;

Don't lose synchronized key word. Making gentInstance method synchronized make sure only one instance in your program (thread safe) when multiple thread invoke getInstance method. To avoid the synchronization overhead I recommend you use first one.