Java单例模式

public class Singleton {

private static Singleton singleton = null;

// 构造方法私有化
private Singleton() {
}

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

public class Singleton {

// 构造方法私有化
private Singleton() {
}

private static Singleton singleton = new Singleton();

public static Singleton getInstance() {
return singleton;
}
}

public class Singleton{

private Singleton(){

}

private static class innerClass {
private static Singleton singleton = new Singleton();
}

public static Singleton getIntance(){
return innerClass.singleton;
}
}