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+/* Adapted from: http://thinking-in-code.blogspot.com/2008/11/duck-typing-in-java-using-dynamic.html */
+
+package de.danoeh.antennapod.util;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.Method;
+import java.lang.reflect.Proxy;
+
+/**
+ * Allows "duck typing" or dynamic invocation based on method signature rather
+ * than type hierarchy. In other words, rather than checking whether something
+ * IS-a duck, check whether it WALKS-like-a duck or QUACKS-like a duck.
+ *
+ * To use first use the coerce static method to indicate the object you want to
+ * do Duck Typing for, then specify an interface to the to method which you want
+ * to coerce the type to, e.g:
+ *
+ * public interface Foo { void aMethod(); } class Bar { ... public void
+ * aMethod() { ... } ... } Bar bar = ...; Foo foo =
+ * DuckType.coerce(bar).to(Foo.class); foo.aMethod();
+ *
+ *
+ */
+public class DuckType {
+
+ private final Object objectToCoerce;
+
+ private DuckType(Object objectToCoerce) {
+ this.objectToCoerce = objectToCoerce;
+ }
+
+ private class CoercedProxy implements InvocationHandler {
+ @Override
+ public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+ Method delegateMethod = findMethodBySignature(method);
+ assert delegateMethod != null;
+ return delegateMethod.invoke(DuckType.this.objectToCoerce, args);
+ }
+ }
+
+ /**
+ * Specify the duck typed object to coerce.
+ *
+ * @param object
+ * the object to coerce
+ * @return
+ */
+ public static DuckType coerce(Object object) {
+ return new DuckType(object);
+ }
+
+ /**
+ * Coerce the Duck Typed object to the given interface providing it
+ * implements all the necessary methods.
+ *
+ * @param
+ * @param iface
+ * @return an instance of the given interface that wraps the duck typed
+ * class
+ * @throws ClassCastException
+ * if the object being coerced does not implement all the
+ * methods in the given interface.
+ */
+ @SuppressWarnings({ "rawtypes", "unchecked" })
+ public <T> T to(Class iface) {
+ assert iface.isInterface() : "cannot coerce object to a class, must be an interface";
+ if (isA(iface)) {
+ return (T) iface.cast(objectToCoerce);
+ }
+ if (quacksLikeA(iface)) {
+ return generateProxy(iface);
+ }
+ throw new ClassCastException("Could not coerce object of type " + objectToCoerce.getClass() + " to " + iface);
+ }
+
+ @SuppressWarnings("rawtypes")
+ private boolean isA(Class iface) {
+ return objectToCoerce.getClass().isInstance(iface);
+ }
+
+ /**
+ * Determine whether the duck typed object can be used with the given
+ * interface.
+ *
+ * @param Type
+ * of the interface to check.
+ * @param iface
+ * Interface class to check
+ * @return true if the object will support all the methods in the interface,
+ * false otherwise.
+ */
+ @SuppressWarnings("rawtypes")
+ public boolean quacksLikeA(Class iface) {
+ for (Method method : iface.getMethods()) {
+ if (findMethodBySignature(method) == null) {
+ return false;
+ }
+ }
+ return true;
+ }
+
+ @SuppressWarnings({ "unchecked", "rawtypes" })
+ private <T> T generateProxy(Class iface) {
+ return (T) Proxy.newProxyInstance(iface.getClassLoader(), new Class[] { iface }, new CoercedProxy());
+ }
+
+ private Method findMethodBySignature(Method method) {
+ try {
+ return objectToCoerce.getClass().getMethod(method.getName(), method.getParameterTypes());
+ } catch (NoSuchMethodException e) {
+ return null;
+ }
+ }
+
+} \ No newline at end of file