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Copier.java

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// file:    Copier.java
// author:  Robert Keller
// purpose: To give a general purpose copy method that will clone if possible,
//          otherwise just return its argument.

import java.lang.reflect.*;     // to use getMethod() and invoke()

/**
 * Copier exists to provide one static method, maybeClone which makes a clone
 * of its argument, or returns the argument itself if not.
 */

class Copier
{
static Class[] noArgs = new Class[0];   // a Class array of size 0
static Object[] args = new Object[0];   // an Object array of size 0

/**
 * Copies an Object, as far as that is possible.
 * If the Object implements the Cloneable interface, then returns a Clone of 
 * the Object.  Otherwise returns the Object itself.
 */

static Object maybeClone(Object ob)
  {
  // One cannot apply clone() to any class unless it implements the Cloneable
  // interface, which class Object does not.  (It does so as a protected
  // method, but we need a public method.)
  //
  // The only means I could find of implementing a method of the desired
  // generality is  to use the "reflection" ideas in java.lang.reflect.  
  // These allow one to determine whether there is a method with a specific
  // name and arguments of a specific type, to get such a method if there is,
  // and to invoke the method on actual arguments.  
  // In our case we are interested in whether the clone()
  // method exists with no arguments.

  if( ob instanceof Cloneable )
    {
    try
      {
      // System.out.println(ob + " is instanceof Cloneable");

      // If Cloneable, clone it.

      return ob.getClass().getMethod("clone", noArgs).invoke(ob, args);
      }
    catch( Exception e)
      {
      // System.out.println(ob + " is not instanceof Cloneable");
      }
    }
  return ob;      // If Otherwise just return the argument.
  }
}

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