我们从两个例子看起：

例子一

package classLoader;class Singleton{        private static Singleton singleton = new Singleton(); public static int counter1; public static int counter2=4; private Singleton(){ Singleton.counter1++; Singleton.counter2++; } public static Singleton getInstance(){ return singleton; } } public class SingletonTest{ public static void main(String[] args){ Singleton singleton = Singleton.getInstance(); System.out.println("counter1:"+singleton.counter1); System.out.println("counter2:"+singleton.counter2); } }

输出结果：

例子二：

package classLoader;class Singleton{        public static int counter1; public static int counter2=4; private static Singleton singleton = new Singleton(); private Singleton(){ Singleton.counter1++; Singleton.counter2++; } public static Singleton getInstance(){ return singleton; } } public class SingletonTest{ public static void main(String[] args){ Singleton singleton = Singleton.getInstance(); System.out.println("counter1:"+singleton.counter1); System.out.println("counter2:"+singleton.counter2); } }

这两个例子只有一处不同，只是调整了 public static int counter1;  public static int counter2=4;  private static Singleton singleton = new Singleton();这三个静态变量的顺序，我们再看看结果：

这是为什么呢？原因就在于加载类时各个成员的加载顺序不同。

我们看一下类的各个成员加载顺序，直接看例子：

package classLoader;public class Demo {                public static void main(String[] args) { subs1 = new Sub(); } } class Super { static int a = getA(); static { System.out.println("加载Super的静态块"); } int b = getB(); { System.out.println("加载Super的普通块"); } Super() { System.out.println("加载Super的构造器"); } static int getA() { System.out.println("加载Super的静态变量"); return 1; } static int getB() { System.out.println("加载Super的实例变量"); return 2; } } class Sub extends Super { static int c = getC(); static { System.out.println("加载Sub的静态块"); } int d = getD(); { System.out.println("加载Sub的普通块"); } Sub() { System.out.println("加载Sub的构造器"); } static int getC() { System.out.println("加载Sub的静态变量"); return 3; } static int getD() { System.out.println("加载Sub的实例变量"); return 4; } }

结果：

从结果来看，可以看到静态成员加载顺序大于普通成员加载顺序，父类大于子类，而对于某个类的成员加载顺序依次为：静态变量 > 静态块 > 普通（实例）变量 > 普通快 > 构造器。对于相同性质的成员，从上到下依次加载。

再回头看开头的两个例子：

　　例子一，先加载private static Singleton singleton = new Singleton();然后调用构造函数，由于此时counter1和counter2还未加载，此时默认先赋值默认初始值0，经过构造函数counter1++和counter2++，分别变成1,1。然后加载 public static int counter1; public static int counter2=4;此时只有counter2重新赋值，所以最终的结果为counter1=1;counter2=4。

　　例子二，先加载 public static int counter1; public static int counter2=4;此时的counter1=0;counter2=4;然后加载private static Singleton singleton = new Singleton();，调用构造方法，构造方法体为counter1++和counter2++，所以最终counter1=1;counter2=5。