Array Class Introspection

JVM Tutorials - Herong's Tutorial Examples

∟Array Class Introspection

This section provides a tutorial example on how to reflect arrays as classes and introspect its properties like superclass, element type, etc.

Arrays are represented as classes in JVM:

All arrays of the same element type and the same dimension are instances of one array class.
On a array class, the getComponentType() method returns the class type of its elements.
The element class type of a multiple dimension array is an array class.

Here is tutorial example program showing you some array classes:

/* ClassArrayReflection.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.lang.reflect.*;
class ClassArrayReflection {
   static java.io.PrintStream out = System.out;
   public static void main(String[] a) {

      out.println("");
      out.println("   byte[] class information...");
      byte[] b = new byte[10];
      arrayIntrospection(b.getClass());

      out.println("");
      out.println("   int[] class information...");
      int[] i = new int[100];
      arrayIntrospection(i.getClass());

      out.println("");
      out.println("   byte[][] class information...");
      byte[][] bb = new byte[10][100];
      arrayIntrospection(bb.getClass());
   }
   public static void arrayIntrospection(Class cls) {
      out.println("Class name:");
      out.println("   "+cls.getName());

      Class p = cls.getSuperclass();
      out.println("Parent class:");
      out.println("   "+p);

      Class t = cls.getComponentType();
      out.println("Element type:");
      out.println("   "+t.getName());

      Constructor[] c  = cls.getDeclaredConstructors();
      out.println("Constructors:");
      for (int i = 0; i<c.length; i++)
         out.println("   "+c[i].toString());

      Field[] f  = cls.getDeclaredFields();
      out.println("Fields:");
      for (int i = 0; i<f.length; i++)
         out.println("   "+f[i].toString());

      Method[] m  = cls.getDeclaredMethods();
      out.println("Methods:");
      for (int i = 0; i<m.length; i++)
         out.println("   "+m[i].toString());
   }
}

When executed, I got this result:

herong>java ClassArrayReflection

   byte[] class information...
Class name:
   [B
Parent class:
   class java.lang.Object
Element type:
   byte
Constructors:
Fields:
Methods:

   int[] class information...
Class name:
   [I
Parent class:
   class java.lang.Object
Element type:
   int
Constructors:
Fields:
Methods:

   byte[][] class information...
Class name:
   [[B
Parent class:
   class java.lang.Object
Element type:
   [B
Constructors:
Fields:
Methods: