枚举是实现单例模式的最佳实践
public class HungryStaticSingleton {
//先静态后动态
//先上,后下
//先属性后方法
private static final HungryStaticSingleton hungrySingleton;
//装个B
static {
hungrySingleton = new HungryStaticSingleton();
}
private HungryStaticSingleton(){}
public static HungryStaticSingleton getInstance(){
return hungrySingleton;
}
}
/**
* 优点:节省了内存,线程安全
* 缺点:性能低
*/
public class LazySimpleSingletion {
private static LazySimpleSingletion instance;
private LazySimpleSingletion(){}
public synchronized static LazySimpleSingletion getInstance(){
if(instance == null){
instance = new LazySimpleSingletion();
}
return instance;
}
}
/**
* 优点:性能高了,线程安全了
* 缺点:可读性难度加大,不够优雅
*/
public class LazyDoubleCheckSingleton {
private volatile static LazyDoubleCheckSingleton instance;
private LazyDoubleCheckSingleton(){}
public static LazyDoubleCheckSingleton getInstance(){
//检查是否要阻塞
if (instance == null) {
synchronized (LazyDoubleCheckSingleton.class) {
//检查是否要重新创建实例
if (instance == null) {
instance = new LazyDoubleCheckSingleton();
//指令重排序的问题
}
}
}
return instance;
}
}
/**
ClassPath : LazyStaticInnerClassSingleton.class
LazyStaticInnerClassSingleton$LazyHolder.class
优点:写法优雅,利用了Java本身语法特点,性能高,避免了内存浪费,不能被反射破坏
缺点:不优雅
*/
public class LazyStaticInnerClassSingleton {
private LazyStaticInnerClassSingleton(){
if(LazyHolder.INSTANCE != null){
throw new RuntimeException("不允许非法访问");
}
}
private static LazyStaticInnerClassSingleton getInstance(){
return LazyHolder.INSTANCE;
}
private static class LazyHolder{
private static final LazyStaticInnerClassSingleton INSTANCE = new LazyStaticInnerClassSingleton();
}
}
/**
* Created by Tom.
* 容器注册式单例
*/
public class ContainerSingleton {
private ContainerSingleton(){}
private static Map<String,Object> ioc = new ConcurrentHashMap<String, Object>();
public static Object getInstance(String className){
Object instance = null;
if(!ioc.containsKey(className)){
try {
instance = Class.forName(className).newInstance();
ioc.put(className, instance);
}catch (Exception e){
e.printStackTrace();
}
return instance;
}else{
return ioc.get(className);
}
}
}
/**
* Created by Tom.
* 枚举式单例,最优雅的单例
*/
public enum EnumSingleton {
INSTANCE;
private Object data;
public Object getData() {
return data;
}
public void setData(Object data) {
this.data = data;
}
public static EnumSingleton getInstance(){return INSTANCE;}
}
public class SeriableSingleton implements Serializable {
//序列化
//把内存中对象的状态转换为字节码的形式
//把字节码通过IO输出流,写到磁盘上
//永久保存下来,持久化
//反序列化
//将持久化的字节码内容,通过IO输入流读到内存中来
//转化成一个Java对象
public final static SeriableSingleton INSTANCE = new SeriableSingleton();
private SeriableSingleton(){}
public static SeriableSingleton getInstance(){
return INSTANCE;
}
private Object readResolve(){ return INSTANCE;}
public static void main(String[] args) {
SeriableSingleton s1 = null;
SeriableSingleton s2 = SeriableSingleton.getInstance();
FileOutputStream fos = null;
try {
fos = new FileOutputStream("SeriableSingleton.obj");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(s2);
oos.flush();
oos.close();
FileInputStream fis = new FileInputStream("SeriableSingleton.obj");
ObjectInputStream ois = new ObjectInputStream(fis);
s1 = (SeriableSingleton)ois.readObject();
ois.close();
System.out.println(s1);
System.out.println(s2);
System.out.println(s1 == s2);
} catch (Exception e) {
e.printStackTrace();
}
}
}
public class ThreadLocalSingleton {
private static final ThreadLocal<ThreadLocalSingleton> threadLocaLInstance =
new ThreadLocal<ThreadLocalSingleton>(){
@Override
protected ThreadLocalSingleton initialValue() {
return new ThreadLocalSingleton();
}
};
private ThreadLocalSingleton(){}
public static ThreadLocalSingleton getInstance(){
return threadLocaLInstance.get();
}
}
原创声明:本文系作者授权腾讯云开发者社区发表,未经许可,不得转载。
如有侵权,请联系 cloudcommunity@tencent.com 删除。
原创声明:本文系作者授权腾讯云开发者社区发表,未经许可,不得转载。
如有侵权,请联系 cloudcommunity@tencent.com 删除。