Java Tutorial/Reflection/Super Class

Get all methods including the inherited method. Using the getMethods(), we can only access public methods.

import java.lang.reflect.Method;
class GetMethods {
  public int add(int numberA, int numberB) {
    return numberA + numberB;
  }
  protected int multiply(int numberA, int numberB) {
    return numberA * numberB;
  }
  private double div(int numberA, int numberB) {
    return numberA / numberB;
  }
}
public class Main {
  public static void main(String[] args) throws Exception {
    GetMethods object = new GetMethods();
    Class clazz = object.getClass();
    Method[] methods = clazz.getMethods();
    for (Method method : methods) {
      System.out.println("Method name        = " + method.getName());
      System.out.println("Method return type = " + method.getReturnType().getName());
      Class[] paramTypes = method.getParameterTypes();
      for (Class c : paramTypes) {
        System.out.println("Param type         = " + c.getName());
      }
    }
    Method method = clazz.getMethod("add", new Class[] { int.class, int.class });
    System.out.println("Method name: " + method.getName());
  }
}

Get super class of an object

public class Main {
  public static void main(String[] args) {
    Object o = new String("Hello");
    Class clazz = o.getClass().getSuperclass();
    System.out.println("Super Class = " + clazz);
    o = new StringIndexOutOfBoundsException("Error message");
    clazz = o.getClass().getSuperclass();
    System.out.println("Super Class = " + clazz);
  }
}

Getting the Superclass of an Object

public class Main {
  public static void main(String[] argv) throws Exception {
    Object o = new String();
    Class sup = o.getClass().getSuperclass(); // java.lang.Object
  }
}

Is Inheritable

//
//$Id: IntrospectionUtil.java 1540 2007-01-19 12:24:10Z janb $
//Copyright 2006 Mort Bay Consulting Pty. Ltd.
//------------------------------------------------------------------------
//Licensed under the Apache License, Version 2.0 (the "License");
//you may not use this file except in compliance with the License.
//You may obtain a copy of the License at 
//http://www.apache.org/licenses/LICENSE-2.0
//Unless required by applicable law or agreed to in writing, software
//distributed under the License is distributed on an "AS IS" BASIS,
//WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//See the License for the specific language governing permissions and
//limitations under the License.
//

import java.lang.reflect.Member;
import java.lang.reflect.Modifier;
public class Utils {
  public static boolean isInheritable(Package pack, Member member) {
    if (pack == null)
      return false;
    if (member == null)
      return false;
    int modifiers = member.getModifiers();
    if (Modifier.isPublic(modifiers))
      return true;
    if (Modifier.isProtected(modifiers))
      return true;
    if (!Modifier.isPrivate(modifiers) && pack.equals(member.getDeclaringClass().getPackage()))
      return true;
    return false;
  }
}

Superclass of Object is null

public class Main {
  public static void main(String[] argv) throws Exception {
    Object o = new Object();
    Class sup = o.getClass().getSuperclass(); // null
  }
}

The superclass of primitive types is always null

public class Main {
  public static void main(String[] argv) throws Exception {
    Class cls = int.class;
    Class sup = cls.getSuperclass(); // null
  }
}