Saturday, August 10, 2013
In our last post we were only concerned in retrieving the declaration details of any class. Today I will go further and try to sniff inside any class. So today I will show you how you can retrieve all the constructors, fields and methods of any class using Java Reflection. For now we will only try to discover all the public members of a class and deal with private ones later. The java.lang.Class provides suitable methods for discovering the members. Here in our sample code we will first take as input the concerned class name and load it using Class.forName(). Then in order to get all its public constructors we vwill use getConstructors(), for fields use getFields() and for methods use getMethods(). An important thing to mention here is that these will return all the public members declared in that class as well as those inherited from its parent. You wont be able to retrieve the private members declarec using these methods. In order to get private members also use getDeclaredConstructors(), getDeclaredFields() and getDeclaredMethods(); but in this case you wont be able to get the inherited members.
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Java Source Code
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import static java.lang.System.out;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class ClassSniffer {
        public static void main(String[] args) {
        out.print("Enter Class Name : ");
        String cname=System.console().readLine();
        try {
        Class c=Class.forName(cname);
        out.println("\n------OUTPUT------");
            //getting all constructors
        out.println("\nConstructors : ");
            Constructor<?> cons[]=c.getConstructors();
            for(Constructor<?> con : cons)
                 out.println("  "+con);
            //getting all fields
            out.println("\nFields : ");
            Field fs[]=c.getFields();
            if(fs.length>0)
                for(Field f : fs)
                      out.println("  "+f);
            else
                out.println("  --No Fields Declared--");
            //getting all methods
            out.println("\nMethods : ");
            Method ms[]=c.getMethods();
            for(Method m : ms)
                     out.println("  "+m);
   } catch (ClassNotFoundException e) {
          e.printStackTrace();
   }
}
}
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Output
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Enter Class Name : ClassSniffer

------OUTPUT------

Constructors :
  public ClassSniffer()

Fields :
  --No Fields Declared--

Methods :
  public static void ClassSniffer.main(java.lang.String[])
  public final void java.lang.Object.wait(long,int) throws java.lang.Interrupted
Exception
  public final native void java.lang.Object.wait(long) throws java.lang.Interrup
tedException
  public final void java.lang.Object.wait() throws java.lang.InterruptedExceptio
n
  public boolean java.lang.Object.equals(java.lang.Object)
  public java.lang.String java.lang.Object.toString()
  public native int java.lang.Object.hashCode()
  public final native java.lang.Class java.lang.Object.getClass()
  public final native void java.lang.Object.notify()
  public final native void java.lang.Object.notifyAll()

NOTE : Here you can see that the methods inherited from Object class are also listed. The name of the class is mentioned just before the method name which shows the methods inherited from other class and those declared in the class itself. Try running this code with getDeclaredConstructors(), getDeclaredFields() and getDeclaredMethods() instead and see the output.
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I am a student of BTech Computer Science Engineering from RCCIIT,Kolkata. I am a crazy lover of Java and wants to settle as a Java developer. I have a seven years Java experience with an application developer experience for 2 years. Recently from March 2012 I am a registered S40 app developer for Nokia and has corrected an app of them. I am currently writing blogs to encourage and grow interest in all those who don't know or learning Java.