dynamicproxymixin39.java

JAVA编程思想第四版英文原版习题答案. pdf原版的

// generics/DynamicProxyMixin39.java
// TIJ4 Chapter Generics, Exercise 39, page 721
// Add a new mixin class Colored to DynamicProxyMixin.java, mix it into mixin and 
// show that it works.
import java.lang.reflect.*;
import java.util.*;
import net.mindview.util.*;
import static net.mindview.util.Tuple.*;

class MixinProxy implements InvocationHandler {
	Map<String,Object> delegatesByMethod;
	public MixinProxy(TwoTuple<Object,Class<?>>... pairs) {
		delegatesByMethod = new HashMap<String,Object>();
		for(TwoTuple<Object,Class<?>> pair : pairs) {
			for(Method method : pair.second.getMethods()) {
				String methodName = method.getName();
				// The first interface in the map
				// implements the method.
				if(!delegatesByMethod.containsKey(methodName))
					delegatesByMethod.put(methodName, pair.first);
			}
		}
	}
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		String methodName = method.getName();
		Object delegate = delegatesByMethod.get(methodName);
		return method.invoke(delegate, args);
	}
	@SuppressWarnings("unchecked")
	public static Object newInstance(TwoTuple... pairs) {
		Class[] interfaces = new Class[pairs.length];
		for(int i = 0; i < pairs.length; i++) {
			interfaces[i] = (Class)pairs[i].second;
		}
		ClassLoader cl = pairs[0].first.getClass().getClassLoader();
		return Proxy.newProxyInstance(cl, interfaces, new MixinProxy(pairs));
	}
}

public class DynamicProxyMixin39 {
	public static void main(String[] args) {
		Object mixin = MixinProxy.newInstance(tuple(new BasicImp(), Basic.class), 
			tuple(new TimeStampedImp(), TimeStamped.class),
			tuple(new SerialNumberedImp(), SerialNumbered.class),
			tuple(new Colored(), Color.class));
		Basic b = (Basic)mixin;
		TimeStamped t = (TimeStamped)mixin;
		SerialNumbered s = (SerialNumbered)mixin;
		b.set("Hello");
		Color c = (Color)mixin;
		System.out.println(b.get());
		System.out.println(t.getStamp());
		System.out.println(s.getSerialNumber());
		System.out.println(c.getColor());		
	}
}