单例模式之静态内部类实现

单例模式之静态内部类实现
直接上代码，懂的都懂，不懂的更要看看：
package singleton;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;

public class InnerSingletonTest {
public static void main(String[] args) throws NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
Constructor declaredconstructor=InnerSingleon.class.getDeclaredConstructor();
declaredconstructor.setAccessible(true);
InnerSingleon instance2=declaredconstructor.newInstance();
InnerSingleon instance1=InnerSingleon.getInstance();
System.out.println(instance1==instance2);
}
}
class InnerSingleon{
private static class InnerSingletonHolder{
private static InnerSingleon instance=new InnerSingleon();
}
//防止反射创建多个实例
private InnerSingleon(){
if(InnerSingletonHolder.instance!=null){
throw new RuntimeException(“单例不允许多个实例”);
}
};

public static InnerSingleon getInstance(){
	return InnerSingletonHolder.instance;
}

}

结果：
Exception in thread “main” java.lang.reflect.InvocationTargetException
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
at singleton.InnerSingletonTest.main(InnerSingletonTest.java:10)
Caused by: java.lang.RuntimeException: 单例不允许多个实例
单例模式的另外一种实现方式。
单例的enum实现方式，不再此处赘述，用枚举类型实现的单例，是无法通过反射，clone，反序列化来破坏单例的。不信的话，动手试试。