Instanceof operator usage

A instanceof B;

 

A must be a specific instance, and B must be a type (or interface ).

 

B cannot be a wildcard parameter.

 

If a determines the specific type during compilation, A must be able to convert (B) A to B. Otherwise, the compiler reports an error.

 

If a cannot be converted to B, you can (object) A instanceof B.

 

If a is actually running, there is no such limit.

 

In the specific example, the following information is obtained on the Forum:

Package instan;

Import java. util. List;

Public class test {

Public static void main (string [] ARGs ){
// The exact type of the reference type returned by GetObject () cannot be determined during compilation. The following two statements can be compiled
System. Out. println (GetObject () instanceof object );
System. Out. println (GetObject () instanceof string );
System. Out. println (GetObject () instanceof test );

// The type can be determined during compilation. If cast can be used, the compilation succeeds; otherwise, the compilation fails.
Test test = new test ();
System. Out. println (test instanceof test); // OK
System. Out. println (test instanceof object); // OK
// System. Out. println (test instanceof string); // error, you can use the following method
System. Out. println (object) test instanceof string );

// Notes related to generics
// List is a generic type. If no generic parameter is specified, the compilation is successful.
System. Out. println (test instanceof list );
// If you do not limit the type limit, compile
System. Out. println (test instanceof list <?> );

// Specify generic parameters. The type can be determined during compilation. If cast is not supported, compilation fails.
// System. Out. println (GetObject () instanceof list <Test>); // Error
// System. Out. println (test instanceof list <Test>); // Error
}

Public static object GetObject (){
Return new test ();
}
}