1、饿汉式：
1 public class Singleton1 { 2 /** 3 * 单例模式之饿汉式 4 */ 5 private static final Singleton1 S1 = new Singleton1(); 6 7 public static final Singleton1 getInstance(){ 8 return S1; 9 } 10 11 private Singleton1() { 12 System.out.println("单例模式之饿汉式"); 13 } 14 }
2、懒汉式：
1 public class Singleton2 { 2 /** 3 * 单例模式之懒汉式 4 */ 5 private static Singleton2 S2 = null; 6 7 public static final Singleton2 getInstance(){ 8 if(S2 == null){ 9 S2 = new Singleton2(); 10 } 11 return S2; 12 } 13 14 private Singleton2() { 15 System.out.println("单例模式之懒汉式"); 16 } 17 }
测试类：
1 public class Test { 2 3 public static void main(String[] args) { 4 5 //测试饿汉式 6 Singleton1 S11 = Singleton1.getInstance(); 7 Singleton1 S12 = Singleton1.getInstance(); 8 9 System.out.println(S11); 10 System.out.println(S12); 11 12 //测试懒汉式 13 Singleton2 S21 = Singleton2.getInstance(); 14 Singleton2 S22 = Singleton2.getInstance(); 15 16 System.out.println(S21); 17 System.out.println(S22); 18 } 19 }
输出：
单例模式之饿汉式
net.stivebone.designpatterns.Singleton1@39e5b5
net.stivebone.designpatterns.Singleton1@39e5b5
单例模式之懒汉式
net.stivebone.designpatterns.Singleton2@5f6303
net.stivebone.designpatterns.Singleton2@5f6303
构造器仅调用了一次，切仅有一个实例。
原文：http://www.cnblogs.com/stivebone/p/5672680.html