Static inner class implementation of singleton mode

Static inner class implementation of singleton mode
Directly upload the code, everyone who understands it can understand it, and those who don’t understand it should read:
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("Singleton does not allow multiple instances"); } };

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

}

Result:
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: Singleton not allowed Multiple instances
Another implementation of the singleton pattern.
The singleton enum implementation method will not be repeated here. A singleton implemented with an enumeration type cannot be destroyed by reflection, clone, or deserialization. If you don't believe me, give it a try.