张龙JVM001中的Singleton

package com.zeph.jvm1;

public class Singleton {

	private static Singleton singleton = new Singleton();
	public static int a;
	public static int b = 0;

	private Singleton() {
		a++;
		b++;
	}

	public static Singleton getSingleton() {
		return singleton;
	}

	public static void main(String[] args) {
		Singleton singleton = Singleton.getSingleton();
		System.out.println(singleton.a);
		System.out.println(singleton.b);
	}
}

  输出1和0，调用类的静态方法，主动加载类，但尚未初始化，然后初始化，首先初始化new Singleton（），此时a=1，b=1，然后初始化b=0，于是输出1和0

package com.zeph.jvm1;

public class Singleton {

	public static int a;
	public static int b = 0;
	private static Singleton singleton = new Singleton();

	private Singleton() {
		a++;
		b++;
	}

	public static Singleton getSingleton() {
		return singleton;
	}

	public static void main(String[] args) {
		Singleton singleton = Singleton.getSingleton();
		System.out.println(singleton.a);
		System.out.println(singleton.b);
	}
}

 输出1和1
反之，最后初始化newSingleton，所以是1和1

引自：http://blog.csdn.net/benw1988/article/details/7606642