Java reflection to get multiple classes

Question

How do i get all of the class names for a .java file using reflection.

When i run the following code it only prints out Boat. I have tried making an array of Classes like:

Class c[] = Class.forName("boat.Boat")

but it results in a syntax error

public class Reflection {
public static void main(String[] args) {
    try {           
         Class c = Class.forName("boat.Boat");
         System.out.println(c.getSimpleName()); 
    } catch(Exception e) {
        e.printStackTrace();
    }
  }
}

Boat.java

package boat;
public class Boat extends Vehicle {
     public Boat() {}
}

class Vehicle {
     public Vehicle() {
         name = "";
     }
     private name;
}

You can't as far as I know without reading the Java source file and parsing it that way. Once the class is compiled it retains no knowledge of the source file location. You can make some educated guesses, like a public class could have come from a Java source file of a similar name, but you can't even do this for the non public classes. — Paul Grime
– Paul Grime, Commented Apr 12, 2013 at 7:15

Sudhanshu Umalkar · Accepted Answer · 2013-04-12 07:15:13Z

3

Even if you write multiple classes in a single .java file (with only one public class), you will get multiple .class files. Hence, you cannot get the list of classes from .java file.

You do have an option of writing a custom parser to parse the .java file and retrieve the class names. Not sure what would be the use of that?

answered Apr 12, 2013 at 7:15

Sudhanshu Umalkar

4,2021 gold badge26 silver badges33 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

AmitG · Accepted Answer · 2013-04-12 07:17:51Z

0

It is the .class file we are providing in Class.forName(""); not .java file. So there is no provision to get all classes from .java file with the usage of Class.forName() method.

answered Apr 12, 2013 at 7:17

AmitG

10.6k5 gold badges33 silver badges55 bronze badges

Comments

dierre · Accepted Answer · 2013-04-12 07:18:10Z

If you are willing to use additional libraries you can use Reflections Project that allows you to search for classes listed in a package.

 Reflections reflections = new Reflections("my.package.prefix");
 //or
 Reflections reflections = new Reflections(ClasspathHelper.forPackage("my.package.prefix"), 
      new SubTypesScanner(), new TypesAnnotationScanner(), new FilterBuilder().includePackage(...), ...);

 //or using the ConfigurationBuilder
 new Reflections(new ConfigurationBuilder()
      .filterInputsBy(new FilterBuilder().includePackage("my.project.prefix"))
      .setUrls(ClasspathHelper.forPackage("my.project.prefix"))
      .setScanners(new SubTypesScanner(), new TypeAnnotationsScanner().filterResultsBy(optionalFilter), ...));

 //then query, for example:
 Set<Class<? extends Module>> modules = reflections.getSubTypesOf(com.google.inject.Module.class);
 Set<Class<?>> singletons =             reflections.getTypesAnnotatedWith(javax.inject.Singleton.class);

 Set<String> properties =       reflections.getResources(Pattern.compile(".*\\.properties"));
 Set<Constructor> injectables = reflections.getConstructorsAnnotatedWith(javax.inject.Inject.class);
 Set<Method> deprecateds =      reflections.getMethodsAnnotatedWith(javax.ws.rs.Path.class);
 Set<Field> ids =               reflections.getFieldsAnnotatedWith(javax.persistence.Id.class);

 Set<Method> someMethods =      reflections.getMethodsMatchParams(long.class, int.class);
 Set<Method> voidMethods =      reflections.getMethodsReturn(void.class);
 Set<Method> pathParamMethods = reflections.getMethodsWithAnyParamAnnotated(PathParam.class);
 Set<Method> floatToString =    reflections.getConverters(Float.class, String.class);

As you can see you can search with different filters. I don't think you can't do for java file but you can search all the classes for package name.

AmitG · Accepted Answer · 2013-04-12 07:28:12Z

0

You can get the superclass of class Boat by calling getSuperclass() on the Class object:

Class<?> c = Boat.class;

Class<?> superClass = c.getSuperclass();
System.out.println(superClass.getSimpleName());  // will print: Vehicle

Look at the API documentation for java.lang.Class.

edited Apr 12, 2013 at 7:28

AmitG

10.6k5 gold badges33 silver badges55 bronze badges

answered Apr 12, 2013 at 7:17

Jesper

208k47 gold badges325 silver badges361 bronze badges

Collectives™ on Stack Overflow

Java reflection to get multiple classes

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related