一、UML
Singleton.png
二、基本步骤
1、私有化构造方法
2、通过一个静态方法或者枚举返回单例对象
3、多线程时保证线程安全
4、确保单例类对象序列化时不会重新构建对象
三、实现方式
1、饿汉式
代码
/**
* @author lizihanglove
* @email one_mighty@163.com
* @date 2018-01-02
* @time 13:02
* @desc 恶汉式单例模式
*/
public class HungrySinglton {
private static HungrySinglton instance = new HungrySinglton();
private HungrySinglton() {
}
public static HungrySinglton getInstance(){
return instance;
}
}
2、懒汉式
代码
/**
* @author lizihanglove
* @email one_mighty@163.com
* @date 2018-01-02
* @time 13:06
* @desc 懒汉式单例
*/
public class LazySingleton {
private static LazySingleton instance;
private LazySingleton() {
}
private static LazySingleton getInstance() {
if (instance == null) {
instance = new LazySingleton();
}
return instance;
}
}
3、双重校验锁式
代码
**
* @author lizihanglove
* @email one_mighty@163.com
* @date 2018-01-02
* @time 13:10
* @desc 双重校验锁单例
*/
public class DoubleCheckLockSingleton {
private static DoubleCheckLockSingleton instance;
private DoubleCheckLockSingleton() {
}
public static DoubleCheckLockSingleton getInstance() {
if (instance == null) {
synchronized (DoubleCheckLockSingleton.class) {
if (instance == null) {
instance = new DoubleCheckLockSingleton();
}
}
}
return instance;
}
}
4、静态内部类式
代码
/**
* @author lizihanglove
* @email one_mighty@163.com
* @date 2018-01-02
* @time 13:14
* @desc 静态内部类单例
*/
public class StaticInnerClassSingleton {
private StaticInnerClassSingleton() {
}
public static StaticInnerClassSingleton getInstance(){
return SingletonHolder.instance;
}
private static class SingletonHolder{
private static final StaticInnerClassSingleton instance= new StaticInnerClassSingleton();
}
}
5、枚举式
代码
/**
* @author lizihanglove
* @email one_mighty@163.com
* @date 2018-01-02
* @time 13:18
* @desc 枚举单列
*/
public enum EnumSingleton {
INSTANCE;
public void doSomething(){
//do something
}
}
6、容器式
代码
/**
* @author lizihanglove
* @email one_mighty@163.com
* @date 2018-01-02
* @time 13:22
* @desc 容器式单例,可忽略
*/
public class ContainerSingleton {
private static Map<String, Object> objectMap = new HashMap<String, Object>();
private ContainerSingleton() {
}
public static void registerInstance(String key, Object value) {
if (!objectMap.containsKey(key)) {
objectMap.put(key, value);
}
}
public static ContainerSingleton getInstance(String key) {
return (ContainerSingleton) objectMap.get(key);
}
