1 public class TestStream { 2     private String name; 3     public String getName() { 4         return name; 5     } 6     public void setName(String name) { 7         this.name = name; 8     }  9     //该类只能有一个实例10     private TestStream(){}    //私有无参构造方法11     //该类必须自行创建12     //有2种方式13     /*private static final TestStream ts=new TestStream();*/14     private static TestStream ts1=null;15     //这个类必须自动向整个系统提供这个实例对象16     public static TestStream getTest(){17         if(ts1==null){18             ts1=new TestStream();19         }20         return ts1;21     }22     public void getInfo(){23         System.out.println("output message "+name);24     }25 }

 1 public class TestMain { 2     public static void main(String [] args){ 3         TestStream s=TestStream.getTest(); 4         s.setName("张孝祥"); 5         System.out.println(s.getName()); 6         TestStream s1=TestStream.getTest(); 7         s1.setName("张孝祥"); 8         System.out.println(s1.getName()); 9         s.getInfo();10         s1.getInfo();11         if(s==s1){12             System.out.println("创建的是同一个实例");13         }else if(s!=s1){14             System.out.println("创建的不是同一个实例");15         }else{16             System.out.println("application error");17         }18     }19 }

 1 //饿汉式单例类.在类初始化时，已经自行实例化  2 public class Singleton1 { 3     //私有的默认构造子 4     private Singleton1() {} 5     //已经自行实例化  6     private static final Singleton1 single = new Singleton1(); 7     //静态工厂方法  8     public static Singleton1 getInstance() { 9         return single;10     }11 }

 1 //懒汉式单例类.在第一次调用的时候实例化  2 public class Singleton2 { 3     //私有的默认构造子 4     private Singleton2() {} 5     //注意，这里没有final     6     private static Singleton2 single=null; 7     //静态工厂方法  8     public synchronized  static Singleton2 getInstance() { 9          if (single == null) {  10              single = new Singleton2();11          }  12         return single;13     }14 }

 1 import java.util.HashMap; 2 import java.util.Map; 3 //登记式单例类. 4 //类似Spring里面的方法，将类名注册，下次从里面直接获取。 5 public class Singleton3 { 6     private static Map<String,Singleton3> map = new HashMap<String,Singleton3>(); 7     static{ 8         Singleton3 single = new Singleton3(); 9         map.put(single.getClass().getName(), single);10     }11     //保护的默认构造子12     protected Singleton3(){}13     //静态工厂方法,返还此类惟一的实例14     public static Singleton3 getInstance(String name) {15         if(name == null) {16             name = Singleton3.class.getName();17             System.out.println("name == null"+"--->name="+name);18         }19         if(map.get(name) == null) {20             try {21                 map.put(name, (Singleton3) Class.forName(name).newInstance());22             } catch (InstantiationException e) {23                 e.printStackTrace();24             } catch (IllegalAccessException e) {25                 e.printStackTrace();26             } catch (ClassNotFoundException e) {27                 e.printStackTrace();28             }29         }30         return map.get(name);31     }32     //一个示意性的商业方法33     public String about() {    34         return "Hello, I am RegSingleton.";    35     }    36     public static void main(String[] args) {37         Singleton3 single3 = Singleton3.getInstance(null);38         System.out.println(single3.about());39     }40 }