Singleton

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Double check

public class Singleton {    private volatile static Singleton instance = null;    private Singleton {    }    public static Singleton getInstance() {        if(instance == null) {            synchronized(Singleton.class) {                if(instance == null) {                    instance = new Singleton();                }            }        }        return instance;    }}

Static innerclass

public class Singleton {    private Singleton {    }    public static Singleton getInstance() {        return SingletonGet.instance;    }    private static class SingletonGet {        private static Singleton instance = new Singleton();    }}