五种单例实现:
(1)饿汉模式:(线程安全,调用率高,但是不能延时加载)
public class Singleton1{
private static Singleton1 singleton1 = new Singleton1();
private Singleton1() {
}
public static Singleton1 getInstance(){
return singleton1;
}
}
(2)懒汉模式:(线程安全,调用率不高,但是可以延时加载)
public class Singleton2{
private static Singleton2 singleton2;
private Singleton2(){
}
public synchronized static Singleton2 getInstance2(){
if(singleton2 == null){
singleton2 = new Singleton2();
}
return singleton2();
}
}
(3)双重检测锁模式:(由于JVM底层模型问题,偶尔会出问题,不建议使用)
public class Singleton3{
private volatile static Singleton3 singleton3;
private Singleton3(){
}
public static Singleton3 getInstance3(){
if(singleton3 == null){
synchronized (Singleton3.class){
if(singleton3 == null){
singleton3 = new Singleton3();
}
}
}
return singleton3;
}
}
(4)静态内部类模式:(线程安全,调用率高,可以延时加载)
- 通过内部类机制使得单例对象可以延迟加载,同时内部类相当于是外部类的静态部分,所以可以通过JVM来保证线程安全。
public class Singleton4{
private static class Singleton4Holder{
private static Singleton4 singleton4 = new Singleton4();
}
private Singleton4(){
}
public static Singleton4 getInstance(){
return Singleton4Holder.singleton4;
}
}
(5)枚举模式:(线程安全,调用率高,不能延时加载,但是可以天然防止反射和反序列化调用)
public enum Singleton5{
singleton5
}
}