java 设计模式-单例模式
作者:互联网
一·单例模式
保证内存中只有一个实例
方法1:用private修饰构造方法
package singleton; public class Mgr01 { private static final Mgr01 INSTANCE = new Mgr01(); private Mgr01(){}; public static Mgr01 getInstance(){return INSTANCE;}; public void m(){ System.out.println("m"); } public static void main(String[] args) { Mgr01 m1 = Mgr01.getInstance(); Mgr01 m2 = Mgr01.getInstance(); System.out.println(m1 == m2); } }
方法2:定义静态语句块
package singleton; public class Mgr01 { private static final Mgr01 INSTANCE; static { INSTANCE = new Mgr01(); } private Mgr01(){}; public static Mgr01 getInstance(){return INSTANCE;}; public void m(){ System.out.println("m"); } public static void main(String[] args) { Mgr01 m1 = Mgr01.getInstance(); Mgr01 m2 = Mgr01.getInstance(); System.out.println(m1 == m2); } }
方法3:懒汉式,线程不安全,使用时需要加锁,会降低效率
package singleton; public class Mgr01 { private static Mgr01 INSTANCE; private Mgr01(){}; public static Mgr01 getInstance(){ if(INSTANCE == null){ INSTANCE = new Mgr01(); } return INSTANCE; }; public void m(){ System.out.println("m"); } public static void main(String[] args) { Mgr01 m1 = Mgr01.getInstance(); Mgr01 m2 = Mgr01.getInstance(); System.out.println(m1 == m2); } }
方法4: 从静态内部类获取实例,相比方法1,只有在调用getInstance的时候才会加载静态内部类,即实现了懒加载,又保证线程安全
package singleton; public class Mgr01 { private Mgr01(){}; private static class Mgr01Holder{ private static final Mgr01 INSTANCE = new Mgr01(); } public static synchronized Mgr01 getInstance(){ return Mgr01Holder.INSTANCE; }; public void m(){ System.out.println("m"); } public static void main(String[] args) { for (int i = 0; i < 100; i++) { new Thread(() -> System.out.println(Mgr01.getInstance().hashCode())).start(); } } }
方法5:枚举单例
package singleton; public enum Mgr08 { INSTANCE; public void m(){} public static void main(String[] args) { for (int i = 0; i < 100; i++) { new Thread(() -> System.out.println(Mgr08.INSTANCE.hashCode())).start(); } } }
标签:java,getInstance,Mgr01,private,INSTANCE,static,单例,设计模式,public 来源: https://www.cnblogs.com/huaweidog/p/16349041.html