Java 單例總結

標籤：

1：懶漢式，不保證安全執行緒

package com.yan.singleton;public class LazySingleton {    private static final LazySingleton instance = null;        private LazySingleton(){}        public static LazySingleton getLazySingleton(){        if(null==instance){            return new LazySingleton();        }                return instance;    }}

2：餓漢式，安全執行緒

package com.yan.singleton;public class HungrySingleton {    private HungrySingleton(){}        private static final HungrySingleton instance = new HungrySingleton();        public static HungrySingleton getInstance(){        return instance;    }}

3：靜態內部類，安全執行緒

package com.yan.singleton;public class InnerClassSingleton {        private InnerClassSingleton(){}        public static final InnerClassSingleton getInstance(){        return InnerClassSingletonHolder.INSTANCE;    }        private static class InnerClassSingletonHolder{        private static final InnerClassSingleton INSTANCE = new InnerClassSingleton();    }}

4：枚舉，安全執行緒，可以還原序列化（推薦此種方式）JDK1.5之後才可以使用

package com.yan.singleton;public enum EnumSingleton {    INSTANCE;        public void todo(){        System.out.println("todo");    }}

 

方式1,2,3都可以使用反射機制來破壞其單例特性，採用枚舉類型可以避免反射的破壞。

例如：

package com.yan.test;import com.yan.singleton.LazySingleton;import java.lang.reflect.Constructor;import java.lang.reflect.InvocationTargetException;import java.util.logging.Level;import java.util.logging.Logger;public class Test {        public static void main(String[] args) {                Constructor<LazySingleton>cs ;                try {            cs = (Constructor<LazySingleton>)                    Class.forName("com.yan.singleton.LazySingleton")                            .getDeclaredConstructor();                        cs.setAccessible(true);//得到私人存取權限，如果不設定，則無法執行個體化對象                            LazySingleton ls = cs.newInstance();                        System.out.println("===ls:"+ls);            System.out.println("===ls:"+cs.newInstance());                    } catch (ClassNotFoundException ex) {            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);        }catch (SecurityException ex) {            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);        } catch (InstantiationException ex) {            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);        } catch (IllegalAccessException ex) {            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);        } catch (IllegalArgumentException ex) {            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);        } catch (InvocationTargetException ex) {            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);        } catch (NoSuchMethodException ex) {            Logger.getLogger(Test.class.getName()).log(Level.SEVERE, null, ex);        }            }}

 

Java 單例總結