Mercurial > hg4j

comparison src/org/tmatesoft/hg/util/Adaptable.java @ 356:91d75e1bac9f

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Consistent approach to deal with adaptable objects. Give adaptable precedence over instanceof to allow conditional response when classes do implement desired interface
author Artem Tikhomirov <tikhomirov.artem@gmail.com>
date Tue, 06 Dec 2011 14:25:52 +0100
parents 1a7a9a20e1f9
children
comparison
equal deleted inserted replaced
355:f2c11fe7f3e9 356:91d75e1bac9f
23 * @author TMate Software Ltd. 23 * @author TMate Software Ltd.
24 */ 24 */
25 public interface Adaptable { 25 public interface Adaptable {
26 26
27 <T> T getAdapter(Class<T> adapterClass); 27 <T> T getAdapter(Class<T> adapterClass);
28
29 class Factory<T> {
30
31 private final Class<T> adapterClass;
32
33 public Factory(Class<T> adapterClass) {
34 assert adapterClass != null;
35 this.adapterClass = adapterClass;
36 }
37
38 public T get(Object target) {
39 return getAdapter(target, adapterClass, null);
40 }
41
42 public T get(Object target, T defaultValue) {
43 return getAdapter(target, adapterClass, defaultValue);
44 }
45
46 /**
47 * Try to adapt target to specified class, resort to defaultValue when not possible.
48 * Instance lookup order is as follows: first, target is checked for being {@link Adaptable} and, if yes,
49 * consulted for adapter. Then, plain {@link Class#isInstance(Object) instanceof} checks if target itself is
50 * of desired type. {@link Adaptable} check comes first to allow classed that are in fact <code>instanceof</code>
51 * desired type to respond to the demand conditionally
52 *
53 * @param target object to adapt, <code>null</code> value, although meaningless, is tolerable.
54 * @param adapterClass desired target class
55 * @param defaultValue value to use if target cannot be adapted to desired class, may be <code>null</code>
56 * @return instance of the desired class
57 */
58 public static <C> C getAdapter(Object target, Class<C> adapterClass, C defaultValue) {
59 if (target instanceof Adaptable) {
60 return ((Adaptable) target).getAdapter(adapterClass);
61 }
62 if (adapterClass.isInstance(target)) {
63 return adapterClass.cast(target);
64 }
65 return defaultValue;
66 }
67 }
28 } 68 }