Mega Code Archive
This program demonstrates the use of proxies and reflection
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/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.Random;
/**
* This program demonstrates the use of proxies.
* @version 1.00 2000-04-13
* @author Cay Horstmann
*/
public class ProxyTest
{
public static void main(String[] args)
{
Object[] elements = new Object[1000];
// fill elements with proxies for the integers 1 ... 1000
for (int i = 0; i < elements.length; i++)
{
Integer value = i + 1;
InvocationHandler handler = new TraceHandler(value);
Object proxy = Proxy.newProxyInstance(null, new Class[] { Comparable.class } , handler);
elements[i] = proxy;
}
// construct a random integer
Integer key = new Random().nextInt(elements.length) + 1;
// search for the key
int result = Arrays.binarySearch(elements, key);
// print match if found
if (result >= 0) System.out.println(elements[result]);
}
}
/**
* An invocation handler that prints out the method name and parameters, then
* invokes the original method
*/
class TraceHandler implements InvocationHandler
{
/**
* Constructs a TraceHandler
* @param t the implicit parameter of the method call
*/
public TraceHandler(Object t)
{
target = t;
}
public Object invoke(Object proxy, Method m, Object[] args) throws Throwable
{
// print implicit argument
System.out.print(target);
// print method name
System.out.print("." + m.getName() + "(");
// print explicit arguments
if (args != null)
{
for (int i = 0; i < args.length; i++)
{
System.out.print(args[i]);
if (i < args.length - 1) System.out.print(", ");
}
}
System.out.println(")");
// invoke actual method
return m.invoke(target, args);
}
private Object target;
}
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