Java/Reflection/Object

Create an object from a string

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Class[] classParm = null;
   Object[] objectParm = null;
   try {
     String name = "java.lang.String";
     Class cl = Class.forName(name);
     java.lang.reflect.Constructor co = cl.getConstructor(classParm);
     System.out.println(co.newInstance(objectParm));
   } catch (Exception e) {
     e.printStackTrace();
     
   }
 }

}

 </source>
   
  
 
  

Determine the Superclass of an Object

   <source lang="java">

import java.util.ArrayList; public class Main {

 public static void main(String[] args) {
   System.out.println(new ArrayList().getClass().getSuperclass().getName());
 }

} //java.util.AbstractList

 </source>
   
  
 
  

Find the Package of an Object

   <source lang="java">

import java.util.ArrayList; import java.util.Vector; public class Main {

 public static void main(String[] args) {
   System.out.println(new Vector().getClass().getPackage().getName());
   System.out.println(new ArrayList().getClass().getPackage().getName());
   System.out.println("Test String".getClass().getPackage().getName());
   System.out.println(new Integer(1).getClass().getPackage().getName());
 }

} /* java.util java.util java.lang java.lang

• /

 </source>
   
  
 
  

For the primitive tipe the interface will be an empty array

   <source lang="java">

import java.util.Calendar; import java.util.Date; public class Main {

 public static void main(String[] args) {
   Date date = Calendar.getInstance().getTime();
   
   Class c = char.class;
   Class[] interfaces = c.getInterfaces();
   for (Class intf : interfaces) {
     System.out.println("Interface Name = " + intf.getName());
   }
 }

}

 </source>
   
  
 
  

Get the class By way of an object

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Object object = new String();
   // By way of an object
   Class cls = object.getClass();
 }

}

 </source>
   
  
 
  

Get the fully-qualified name of a class

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Class cls = java.lang.String.class;
   String name = cls.getName(); 
   System.out.println(name);
 }

}

 </source>
   
  
 
  

Get the fully-qualified name of a inner class

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Class cls = java.util.Map.Entry.class;
   String name = cls.getName(); 
   System.out.println(name);
 }

}

 </source>
   
  
 
  

Get the name of an array

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   String name = boolean[].class.getName();
   System.out.println(name);
   name = byte[].class.getName();
   System.out.println(name);
   name = char[].class.getName();
   System.out.println(name);
   name = short[].class.getName();
   System.out.println(name);
   name = int[].class.getName();
   System.out.println(name);
   name = long[].class.getName();
   System.out.println(name);
   name = float[].class.getName();
   System.out.println(name);
   name = double[].class.getName();
   System.out.println(name);
   name = String[].class.getName();
   System.out.println(name);
   name = int[][].class.getName();
   System.out.println(name);
 }

}

 </source>
   
  
 
  

Get the name of a primitive type

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   String name = int.class.getName(); // int
   System.out.println(name);
 }

}

 </source>
   
  
 
  

Get the name of void

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Class cls = Void.TYPE;
   String name = cls.getName(); // void
 }

}

 </source>
   
  
 
  

Get the unqualified name of a class

   <source lang="java">

public class Main {

 public static void main(String[] argv) throws Exception {
   Class cls = java.util.Map.Entry.class;
   String name = cls.getName();
   if (name.lastIndexOf(".") > 0) {
     name = name.substring(name.lastIndexOf(".") + 1); // Map$Entry
     name = name.replace("$", ".");      // Map.Entry
   }
 }

}

 </source>
   
  
 
  

Getting the Superclass of a Class Object

   <source lang="java">

public class Main {

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

}

 </source>
   
  
 
  

If a class object is an interface or a class

   <source lang="java">

public class Main {

 public static void main(String[] args) {
   // Checking whether Cloneable is an interface or class
   Class clazz = Cloneable.class;
   boolean isInterface = clazz.isInterface();
   System.out.println("Is Interface = " + isInterface);
 }

}

 </source>
   
  
 
  

Instantiate unknown class at runtime and call the object"s methods

   <source lang="java">

import java.lang.reflect.Method; public class Main {

 public static void main(String[] args) throws Exception {
   Class myclass = Class.forName("java.lang.String");
   Method[] methods = myclass.getMethods();
   //Object object = myclass.newInstance();
   for (int i = 0; i < methods.length; i++) {
     System.out.println(methods[i].getName());
     //System.out.println(methods[i].invoke(object));
   }
 }

} /* hashCode compareTo compareTo indexOf indexOf indexOf indexOf equals toString charAt codePointAt codePointBefore codePointCount compareToIgnoreCase concat contains contentEquals contentEquals copyValueOf copyValueOf endsWith equalsIgnoreCase format format getBytes getBytes getBytes getBytes getChars intern isEmpty lastIndexOf lastIndexOf lastIndexOf lastIndexOf length matches offsetByCodePoints regionMatches regionMatches replace replace replaceAll replaceFirst split split startsWith startsWith subSequence substring substring toCharArray toLowerCase toLowerCase toUpperCase toUpperCase trim valueOf valueOf valueOf valueOf valueOf valueOf valueOf valueOf valueOf getClass wait wait wait notify notifyAll

• /

 </source>
   
  
 
  

Obtain from where a Class is loaded

   <source lang="java">

public class Main {

 public static void main(String args[]) {
   Main m = new Main();
   System.out.println(m.getClass().getName() + " is loaded from "
       + m.getClass().getProtectionDomain().getCodeSource().getLocation());
 }

}

 </source>
   
  
 
  

Using Reflection to browse a java class

   <source lang="java">

import java.lang.reflect.Constructor; import java.lang.reflect.Field; import java.lang.reflect.Method; public class Main {

 public static void main(String argv[]) throws Exception{
   String className = "String";
   Class c = Class.forName(className);
   Constructor cst[] = c.getDeclaredConstructors();
   // get fields from the Class object
   Field f[] = c.getDeclaredFields();
   // get methods from the Class object
   Method m[] = c.getDeclaredMethods();
   // filling the constructors list box
   for (int i = 0; i < cst.length; i++) {
     System.out.println(cst[i].getName());
   }
   // filling the fields list box
   for (int i = 0; i < f.length; i++) {
     System.out.println(f[i].getName());
   }
   // filling the methods list box
   for (int i = 0; i < m.length; i++) {
     System.out.println(m[i].getName());
   }
 }

}

 </source>