Java/Reflection/Array Reflection

Array Reflection: create instance

   <source lang="java">
 

/* From http://java.sun.ru/docs/books/tutorial/index.html */ /*

* Copyright (c) 1995-1998 Sun Microsystems, Inc. All Rights Reserved.
* 
* Permission to use, copy, modify, and distribute this software and its
* documentation for NON-COMMERCIAL purposes and without fee is hereby granted
* provided that this copyright notice appears in all copies. Please refer to
* the file "copyright.html" for further important copyright and licensing
* information.
* 
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
* SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
* WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
* NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY
* LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES.
*/

import java.lang.reflect.Array; public class SampleCreateArrayReflection {

 public static void main(String[] args) {
   int[] originalArray = { 55, 66 };
   int[] biggerArray = (int[]) doubleArray(originalArray);
   System.out.println("originalArray:");
   for (int k = 0; k < Array.getLength(originalArray); k++)
     System.out.println(originalArray[k]);
   System.out.println("biggerArray:");
   for (int k = 0; k < Array.getLength(biggerArray); k++)
     System.out.println(biggerArray[k]);
 }
 static Object doubleArray(Object source) {
   int sourceLength = Array.getLength(source);
   Class arrayClass = source.getClass();
   Class componentClass = arrayClass.getComponentType();
   Object result = Array.newInstance(componentClass, sourceLength * 2);
   System.arraycopy(source, 0, result, 0, sourceLength);
   return result;
 }

}

 </source>
   
  
 
  

Array Reflection: getComponentType()

   <source lang="java">
 

/* From http://java.sun.ru/docs/books/tutorial/index.html */ /*

* Copyright (c) 1995-1998 Sun Microsystems, Inc. All Rights Reserved.
* 
* Permission to use, copy, modify, and distribute this software and its
* documentation for NON-COMMERCIAL purposes and without fee is hereby granted
* provided that this copyright notice appears in all copies. Please refer to
* the file "copyright.html" for further important copyright and licensing
* information.
* 
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
* SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
* WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
* NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY
* LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES.
*/

import java.awt.Button; public class SampleComponentReflection {

 public static void main(String[] args) {
   int[] ints = new int[2];
   Button[] buttons = new Button[6];
   String[][] twoDim = new String[4][5];
   printComponentType(ints);
   printComponentType(buttons);
   printComponentType(twoDim);
 }
 static void printComponentType(Object array) {
   Class arrayClass = array.getClass();
   String arrayName = arrayClass.getName();
   Class componentClass = arrayClass.getComponentType();
   String componentName = componentClass.getName();
   System.out.println("Array: " + arrayName + ", Component: "
       + componentName);
 }

}

 </source>
   
  
 
  

Array Reflection: get length

   <source lang="java">
 

/* From http://java.sun.ru/docs/books/tutorial/index.html */ /*

* Copyright (c) 1995-1998 Sun Microsystems, Inc. All Rights Reserved.
* 
* Permission to use, copy, modify, and distribute this software and its
* documentation for NON-COMMERCIAL purposes and without fee is hereby granted
* provided that this copyright notice appears in all copies. Please refer to
* the file "copyright.html" for further important copyright and licensing
* information.
* 
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
* SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
* WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
* NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY
* LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES.
*/

import java.lang.reflect.Array; public class SampleGetArrayReflection {

 public static void main(String[] args) {
   int[] sourceInts = { 12, 78 };
   int[] destInts = new int[2];
   copyArray(sourceInts, destInts);
   String[] sourceStrgs = { "Hello ", "there ", "everybody" };
   String[] destStrgs = new String[3];
   copyArray(sourceStrgs, destStrgs);
 }
 public static void copyArray(Object source, Object dest) {
   for (int i = 0; i < Array.getLength(source); i++) {
     Array.set(dest, i, Array.get(source, i));
     System.out.println(Array.get(dest, i));
   }
 }

}

 </source>
   
  
 
  

Array Reflection: Multi Array Reflection

   <source lang="java">
 

/* From http://java.sun.ru/docs/books/tutorial/index.html */ /*

* Copyright (c) 1995-1998 Sun Microsystems, Inc. All Rights Reserved.
* 
* Permission to use, copy, modify, and distribute this software and its
* documentation for NON-COMMERCIAL purposes and without fee is hereby granted
* provided that this copyright notice appears in all copies. Please refer to
* the file "copyright.html" for further important copyright and licensing
* information.
* 
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
* SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
* WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
* NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY
* LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES.
*/

import java.lang.reflect.Array; public class SampleMultiArrayReflection {

 public static void main(String[] args) {
   // The oneDimA and oneDimB objects are one dimensional int arrays
   // with 5 elements.
   int[] dim1 = { 5 };
   int[] oneDimA = (int[]) Array.newInstance(int.class, dim1);
   int[] oneDimB = (int[]) Array.newInstance(int.class, 5);
   // The twoDimStr object is a 5 X 10 array of String objects.
   int[] dimStr = { 5, 10 };
   String[][] twoDimStr = (String[][]) Array.newInstance(String.class,
       dimStr);
   // The twoDimA object is an array of 12 int arrays. The tail
   // dimension is not defined. It is equivalent to the array
   // created as follows:
   //    int[][] ints = new int[12][];
   int[] dimA = { 12 };
   int[][] twoDimA = (int[][]) Array.newInstance(int[].class, dimA);
 }

}

 </source>
   
  
 
  

Array Reflection: name and type

   <source lang="java">
 

/* From http://java.sun.ru/docs/books/tutorial/index.html */ /*

* Copyright (c) 1995-1998 Sun Microsystems, Inc. All Rights Reserved.
* 
* Permission to use, copy, modify, and distribute this software and its
* documentation for NON-COMMERCIAL purposes and without fee is hereby granted
* provided that this copyright notice appears in all copies. Please refer to
* the file "copyright.html" for further important copyright and licensing
* information.
* 
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
* SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
* WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
* NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY
* LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
* DERIVATIVES.
*/

import java.awt.Button; import java.awt.TextField; import java.lang.reflect.Field; public class SampleArrayReflection {

 public static void main(String[] args) {
   KeyPad target = new KeyPad();
   printArrayNames(target);
 }
 static void printArrayNames(Object target) {
   Class targetClass = target.getClass();
   Field[] publicFields = targetClass.getFields();
   for (int i = 0; i < publicFields.length; i++) {
     String fieldName = publicFields[i].getName();
     Class typeClass = publicFields[i].getType();
     String fieldType = typeClass.getName();
     if (typeClass.isArray()) {
       System.out.println("Name: " + fieldName + ", Type: "
           + fieldType);
     }
   }
 }

} class KeyPad {

 public boolean alive;
 public Button power;
 public Button[] letters;
 public int[] codes;
 public TextField[] rows;
 public boolean[] states;

}

 </source>
   
  
 
  

Check if the given object is an array (primitve or native).

   <source lang="java">

import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; /*

* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/

public class Main {

 /**
  * Check if the given object is an array (primitve or native).
  *
  * @param obj  Object to test.
  * @return     True of the object is an array.
  */
 public static boolean isArray(final Object obj) {
    if (obj != null)
       return obj.getClass().isArray();
    return false;
 }

}

 </source>
   
  
 
  

Creating an Array: A 10x20 2-dimensional int array.

   <source lang="java">
 

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

 public static void main(String[] argv) throws Exception {
   int[][] ints2 = (int[][]) Array.newInstance(int.class, new int[] { 10, 20 });
 }

}

 </source>
   
  
 
  

Creating an Array: An array of 10 int-arrays.

   <source lang="java">
 

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

 public static void main(String[] argv) throws Exception {
   int[][] ints2 = (int[][]) Array.newInstance(int[].class, 10);
 }

}

 </source>
   
  
 
  

Creating an Array: An array of 10 ints.

   <source lang="java">
 

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

 public static void main(String[] argv) throws Exception {
   int[] ints = (int[]) Array.newInstance(int.class, 10);
 }

}

 </source>
   
  
 
  

Determining If an Object Is an Array

   <source lang="java">
 

public class Main {

 public static void main(String[] argv) throws Exception {
   boolean b = "".getClass().isArray();
   if (b) {
     System.out.println("object is an array");
   }
 }

}

 </source>
   
  
 
  

Getting and Setting the Value of an Element in an Array Object

   <source lang="java">
 

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

 public static void main(String[] argv) throws Exception {
   int[] array = { 1, 2, 3 };
   // Get the value of the third element.
   Object o = Array.get(array, 2);
   // Set the value of the third element.
   Array.set(array, 2, 1);
 }

}

 </source>
   
  
 
  

Getting the Component Type of an Array Object

   <source lang="java">
 

public class Main {

 public static void main(String[] argv) throws Exception {
   Object o = new int[1][2][3];
   o.getClass().getComponentType();
 }

}

 </source>
   
  
 
  

Getting the Length and Dimensions of an Array Object

   <source lang="java">
 

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

 public static void main(String[] argv) throws Exception {
   Object o = new int[1][2][3];
   int len = Array.getLength(o); // 1
   System.out.println(len);
   int dim = getDim(o); // 3
   System.out.println(dim);
 }
 public static int getDim(Object array) {
   int dim = 0;
   Class cls = array.getClass();
   while (cls.isArray()) {
     dim++;
     cls = cls.getComponentType();
   }
   return dim;
 }

}

 </source>
   
  
 
  

return an Object array for the given object.

   <source lang="java">

import java.lang.reflect.Array; /*

* JBoss, Home of Professional Open Source
* Copyright 2005, JBoss Inc., and individual contributors as indicated
* by the @authors tag. See the copyright.txt in the distribution for a
* full listing of individual contributors.
*
* This is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this software; if not, write to the Free
* Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA, or see the FSF site: http://www.fsf.org.
*/

public class Main {

 /**
  * @return an Object array for the given object.
  *
  * @param obj  Object to convert to an array.  Converts primitive
  *             arrays to Object arrays consisting of their wrapper
  *             classes.  If the object is not an array (object or primitve)
  *             then a new array of the given type is created and the
  *             object is set as the sole element.
  */
 public static Object[] toArray(final Object obj) {
    // if the object is an array, the cast and return it.
    if (obj instanceof Object[]) {
       return (Object[])obj;
    }
    // if the object is an array of primitives then wrap the array
    Class type = obj.getClass();
    Object array; 
    if (type.isArray()) {
       int length = Array.getLength(obj);
       Class componentType = type.getComponentType();
       array = Array.newInstance(componentType, length);
       for (int i=0; i<length; i++) {
          Array.set(array, i, Array.get(obj, i));
       }
    }
    else {
       array = Array.newInstance(type, 1);
       Array.set(array, 0, obj);
    }
    return (Object[])array;
 }

}

 </source>
   
  
 
  

Using reflection to check array type and length

   <source lang="java">
 

import java.lang.reflect.Array; public class MainClass {

 public static void main(String args[]) {
   String data[] = new String[3];
   data[0] = "Java";
   printType(data);
 }
 private static void printType(Object object) {
   Class type = object.getClass();
   if (type.isArray()) {
     Class dataType = type.getComponentType();
     System.out.println("Array of: " + dataType);
     System.out.println(" Length: " + Array.getLength(object));
   }
 }

}

 </source>
   
  
 
  

Using reflection to create, fill, and display an array

   <source lang="java">
 

import java.lang.reflect.Array; import java.util.Random; public class MainClass {

 public static void main(String args[]) {
   Object array = Array.newInstance(int.class, 3);
   printType(array);
   fillArray(array);
   displayArray(array);
 }
 private static void printType(Object object) {
   Class type = object.getClass();
   if (type.isArray()) {
     Class elementType = type.getComponentType();
     System.out.println("Array of: " + elementType);
     System.out.println("Array size: " + Array.getLength(object));
   }
 }
 private static void fillArray(Object array) {
   int length = Array.getLength(array);
   Random generator = new Random(System.currentTimeMillis());
   for (int i = 0; i < length; i++) {
     int random = generator.nextInt();
     Array.setInt(array, i, random);
   }
 }
 private static void displayArray(Object array) {
   int length = Array.getLength(array);
   for (int i = 0; i < length; i++) {
     int value = Array.getInt(array, i);
     System.out.println("Position: " + i + ", value: " + value);
   }
 }

}

 </source>