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Java Tutorial » Reflection » Class  
7.1.8.Demonstrates Dynamic class type checkingPrevious/Next
/*
 *     file: DynamicTypeChecking.java
 *  package: oreilly.hcj.reflection
 *
 * This software is granted under the terms of the Common Public License,
 * CPL, which may be found at the following URL:
 * http://www-124.ibm.com/developerworks/oss/CPLv1.0.htm
 *
 * Copyright(c) 2003-2005 by the authors indicated in the @author tags.
 * All Rights are Reserved by the various authors.
 *
 ########## DO NOT EDIT ABOVE THIS LINE ########## */

import java.io.Serializable;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * Demonstrates Dynamic class type checking.
 
 @author <a href=mailto:kraythe@arcor.de>Robert Simmons jr. (kraythe)</a>
 @version $Revision: 1.3 $
 */
public class DynamicTypeChecking {
  /**
   * Demonstrates usage of <tt>isAssignableFrom</tt> on a class object.
   
   @param dataType
   *          The data type to check.
   
   @return The value <tt>true</tt> if the class is a descendant of
   *         <tt>java.lang.Number</tt> or <tt>false</tt> if it isnt.
   */
  public static boolean isNumber(final Class dataType) {
    return Number.class.isAssignableFrom(dataType);
  }

  /**
   * Demonstration Method.
   
   @param args
   *          Command Line arguments.
   */
  public static void main(final String[] args) {

    final Set classes = new HashSet();
    classes.add(Class.class);
    classes.add(Comparable.class);
    classes.add(Serializable.class);
    classes.add(Integer.class);
    classes.add(int.class);
    classes.add(Float[].class);
    classes.add(String.class);
    classes.add(double[].class);
    classes.add(boolean.class);
    System.out.println("Using isAssignableFrom:");
    useAssignable(classes);
    System.out.println("\nUsing isInstance:");
    useIsInstance(classes);
  }

  /**
   * Demonstrates use of <tt>isAssignableFrom</tt> on objects in a set.
   
   @param inputSet
   *          The set to check.
   */
  public static void useAssignable(final Set inputSet) {
    final Iterator iter = inputSet.iterator();
    Object obj = null;

    while (iter.hasNext()) {
      obj = iter.next();
      if (obj != null) {
        if (Number.class.isAssignableFrom(obj.getClass())) {
          System.out.println(obj);
        }
      }
    }
  }

  /**
   * Demonstrates usage of <tt>isInstance</tt> on objects in a set.
   
   @param inputSet
   *          The set to check.
   */
  public static void useIsInstance(final Set inputSet) {
    final Iterator iter = inputSet.iterator();
    Object obj = null;

    while (iter.hasNext()) {
      obj = iter.next();
      if (Number.class.isInstance(obj)) {
        System.out.println(obj);
      }
    }
  }

  /**
   * Demonstration method for class comparison based on passed class and object.
   
   @param dataType
   *          The data type to check.
   @param inputSet
   *          The input set to check.
   
   @throws NullPointerException
   *           If the data type given is null.
   */
  public static void useIsInstance2(final Class dataType, final Set inputSet) {
    if (dataType == null) {
      throw new NullPointerException();
    }

    final Iterator iter = inputSet.iterator();
    Object obj = null;

    while (iter.hasNext()) {
      obj = iter.next();
      if (dataType.isInstance(obj)) {
        System.out.println(obj);
      }
    }
  }

  /**
   * A bad version of useInstance. If you uncomment this method you will get a
   * compiler error.
   */

  // public static void useIsInstance3(final Class dataType, final Set inputSet)
  // {
  // final Iterator iter = inputSet.iterator();
  // Object obj = null;
  // while (iter.hasNext()) {
  // obj = iter.next();
  // if (obj instanceof dataType) {
  // System.out.println(obj);
  // }
  // }
  // }
}

/* ########## End of File ########## */
7.1.Class
7.1.1. Get class name for various object
7.1.2. Create new instance
7.1.3. Get Canonical Name for a class
7.1.4. Demonstrates the use of getDeclaringClass()
7.1.5. Demonstrates the use of instance comparisons
7.1.6. Demonstrates usage of various class information methods
7.1.7. Demonstrates how to get declaration information on a Class
7.1.8. Demonstrates Dynamic class type checking
7.1.9. Demonstrates how to set public field objects
7.1.10. Demonstrates fetching nested class info from a Class object
7.1.11. Demonstration of how to obtain instances of java.lang.Class
7.1.12. Demonstrates getting immediate superclass info
7.1.13. Get declared method by name and parameter type
7.1.14. get class from an object
7.1.15. Returns the name of a class without the package name
7.1.16. Class comparator: compare and sort classes and their superclasses.
7.1.17. Is Type Compatible
7.1.18. Is the Same Signature
7.1.19. Determine whether the supplied string represents a well-formed fully-qualified Java classname.