check whether a object is interface or class

[rajeev]

public class CheckForInterface {

	public static  void main(String[] args) throws ClassNotFoundException {
		Class class1=Class.forName("OneClass");
		Class class2=Class.forName("MyInterface");

		System.out.println(class1.isLocalClass());
		System.out.println(class1.isInterface());
		System.out.println(class2.isInterface());

	}
}

interface MyInterface {

}

public class OneClass {

}

The above code showing output
false
false
true

"OneClass" is a class still it is printing false..........then how can check it is a class or not..........is there any other code?

[jim829]

That shouldn't even compile. OneClass should be in its own file since it is declare public.

Regards,
Jim

[allaudin]

Because class one is not a local class .
see Local Classes (The Java™ Tutorials > Learning the Java Language > Classes and Objects)

[allaudin]

right jim

[rajeev]

public class CheckForInterface {
 
    public static  void main(String[] args) throws ClassNotFoundException {
        Class class1=Class.forName("OneClass");
        Class class2=Class.forName("MyInterface");
 
        System.out.println(class1.isLocalClass());
        System.out.println(class1.isInterface());
        System.out.println(class2.isInterface());
 
    }
}

interface MyInterface {
 
}

 
public class OneClass {
 
}

all these classes and interface are in separate files..................how can i check the object class1,class2 is class type or interface type.............

[JosAH]

Everything in Java is a type; classes and interaces are types; if something isn't an interface it must be a class; the Class object can tell what sort of class it is: local, anonymous, member (or simply a top level class).

kind regards,

Jos

[gimbal2]

"OneClass" is a class still it is printing false..........then how can check it is a class or not

Its not an interface, so if you ask it "are you an interface" it is going to reply FALSE! Or perhaps you were referring to the isLocalClass() call?

I must admit that I don't even know what a local class is. What I do know is that OneClass is not a local class.

[DarrylBurke]

I'm not terribly sure, but I think a local class is one that's declared inside a method, constructor or initializer.

db

[gimbal2]

I was guessing more towards that it is a standard JDK class or something. But your idea seems more plausible.

[jim829]

I did some testing on this. I find the tests rely on the actual .class name which includes either a $ or a $ followed by a digit in the name.

package examples;

public class ClassTest {

   public static void main(String[] args) throws ClassNotFoundException{
      // TODO Auto-generated method stub
      new ClassTest().startUp();
   }
   public void startUp() throws ClassNotFoundException {
      Class<?> firstLocalClass = foo(1).getClass();
      Class<?> secondLocalClass = foo(2).getClass();
      Class<?> firstLocalClass1 = foo1(1).getClass();
      Class<?> secondLocalClass1 = foo1(2).getClass();
      Class<?> thirdLocalClass1 = foo1(3).getClass();
      Class<?> memberClass = (this.new MemberClass()).getClass();
      Class<?> interfaceType = Class.forName("examples.Interface");
      
      
      System.out.println(firstLocalClass.getName() + " = " + firstLocalClass.isLocalClass());
      System.out.println(secondLocalClass.getName() + " = " +secondLocalClass.isLocalClass());
      System.out.println(firstLocalClass1.getName() + " = " + firstLocalClass1.isLocalClass());
      System.out.println(secondLocalClass1.getName() + " = " +secondLocalClass1.isLocalClass());
      System.out.println(thirdLocalClass1.getName() + " = " +thirdLocalClass1.isLocalClass());
      System.out.println(memberClass.getName() + " = " +memberClass.isMemberClass());
      System.out.println(interfaceType.getName() + " = " +interfaceType.isInterface());
      
      System.out.println("Testing for anonymous classes");
      ClassTest anon1 = new ClassTest() {};
      ClassTest anon2 = new ClassTest() {};
      Class<?> anon1Class = anon1.getClass();
      Class<?> anon2Class = anon2.getClass();
      
      System.out.println(anon1Class.getName() + " = " + anon1Class.isAnonymousClass());
      System.out.println(anon2Class.getName() + " = " + anon2Class.isAnonymousClass());
   }
 
   public Object foo(int which) {
      class FirstLocalClass {}
      class SecondLocalClass {}
      switch (which) {
         case 1:
            return new FirstLocalClass();
         case 2:
            return new SecondLocalClass();
      }
      return null;
   }
   public Object foo1(int which) {
      class FirstLocalClass {}
      class SecondLocalClass {}
      class ThirdLocalClass {}
      switch (which) {
         case 1:
            return new FirstLocalClass();
         case 2:
            return new SecondLocalClass();
         case 3:
            return new ThirdLocalClass();
      }
      return null;
   }
   
   public class MemberClass{
      MemberClass(){}  
   }
}

interface Interface {}

When run, the following output was produced:

examples.ClassTest$1FirstLocalClass = true
examples.ClassTest$1SecondLocalClass = true
examples.ClassTest$2FirstLocalClass = true
examples.ClassTest$2SecondLocalClass = true
examples.ClassTest$1ThirdLocalClass = true
examples.ClassTest$MemberClass = true
examples.Interface = true

Testing for anonymous classes
examples.ClassTest$1 = true
examples.ClassTest$2 = true

A couple observations:

1. Local class names have a digit after the $. It only changes when the names are duplicated in other methods.
2. I could not seem to get an instantiated designation of an interface to return true. I had to specify the name in Class.forName. All instantiations or assignments of interfaces are reported as false for isInterface().
3. I didn't do an exhaustive test for false reports. But what I did test above reported false when applied to other type checks.


Edit: Idiot! I left out the foo1() method and calls. At least now the code matches the output. Shouldn't affect any previous posts.

Regards,
Jim

[chandrasekhar.melam]

public class OneClass {

}

i have small doubt in the ave program that is , is it possible to define two public classes in a program? in the above program there are two public classes one is OneClass and another one is CheckForInterface

[rajeev]

i got it thanx.......

[allaudin]

i have small doubt in the ave program that is , is it possible to define two public classes in a program? in the above program there are two public classes one is OneClass and another one is CheckForInterface

Rajeev already said that "all these classes and interface are in separate files". and yes it is possible to define two public classes in a programe but defining two public classes in a single source file is not possible ...

[allaudin]

I did some testing on this. I find the tests rely on the actual .class name which includes either a $ or a $ followed by a digit in the name.

When run, the following output was produced:

examples.ClassTest$1FirstLocalClass = true
examples.ClassTest$1SecondLocalClass = true
examples.ClassTest$2FirstLocalClass = true
examples.ClassTest$2SecondLocalClass = true
examples.ClassTest$1ThirdLocalClass = true
examples.ClassTest$MemberClass = true
examples.Interface = true

Testing for anonymous classes
examples.ClassTest$1 = true
examples.ClassTest$2 = true

A couple observations:

1. Local class names have a digit after the $. It only changes when the names are duplicated in other methods.

Are these synthetic classes ? I don't know the exact definition but I think their names have $ sign

[allaudin]

     
      
      System.out.println("Testing for anonymous classes");
      ClassTest anon1 = new ClassTest() {}; 
      ClassTest anon2 = new ClassTest() {};
      Class<?> anon1Class = anon1.getClass();
      Class<?> anon2Class = anon2.getClass();
      
      System.out.println(anon1Class.getName() + " = " + anon1Class.isAnonymousClass());
      System.out.println(anon2Class.getName() + " = " + anon2Class.isAnonymousClass());
   }

How are these anonymous classes ? I read that anonymous classes are those which donot hava names ...

[DarrylBurke]

How are these anonymous classes ? I read that anonymous classes are those which donot hava names ...

Try running this line of code:

System.out.println(new Object() {}.getClass().getName());

db

[jim829]

I would say not. Since isSynthetic returns false for anonymous classes. The JLS says this:

Chapter*13.*Binary Compatibility

"7. Any constructs introduced by a Java compiler that do not have a corresponding construct in the source code must be marked as synthetic, except for default constructors, the class initialization method, and the values and valueOf methods of the Enum class."

So I would equate a synthetic class as similar to a regular class as a bridge method is to a regular method within generics. The compiler generates bridge methods to help with wildcard capture situations, yet they don't appear in the code. I have never seen a synthetic class nor can I give an example of how one is manifested.

I had never heard of any of these terms until this thread.

Regards,
Jim

[allaudin]

Try running this line of code:

System.out.println(new Object() {}.getClass().getName());

db

you mean $(digit) is for anonymous and local classes ?

[allaudin]

Can't understand why is this

 Class<?> anon1Class = anon1.getClass();

anonymouse .. it shouldn't be ClassTest ????

[jim829]

No because anon1Class is an instance of an anonymous class.

Class Foo {
    public void cheer() {
          System.out.println("Rah!");
    }
}

Foo f1 = new Foo();  // regular instance, not anonymous
Foo f2 = new Foo() { // creating anonymous instance
       public void cheer() {
            System.out.println("Ole!");
       }
 };

f2 is anonymous. What is the name of the instance which overrides method()?

This is also anonymous (doesn't override anything but note the syntax).

Foo f3 = new Foo() {};

Regards,
Jim