方法1：

/**
* Created by Genji on 2015/10/25.
*/
public class Singleton {
private static final Singleton INSTANCE = new Singleton();
private Singleton() {

}
public void doSomething() {
}

}

方法2：

/**
* Created by Genji on 2015/10/25.
*/
public class Singleton {
private static final Singleton INSTANCE = new Singleton();
private Singleton() {

}
public static Singleton getInstance() {

return INSTANCE;

}
public void doSomething() {
}

}

以上两种方法都将构造器私有化。下面这种方法不同于上面两种:

/**
* Created by Genji on 2015/10/25.
*/
public enum Singleton {
INSTANCE;
public void doSomething() {

}

}

连构造方法都没有了，非常简洁。