1 /*
2  * Copyright (C) 2011 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package android.util;
17 
18 
19 /**
20  * A property is an abstraction that can be used to represent a <emb>mutable</em> value that is held
21  * in a <em>host</em> object. The Property's {@link #set(Object, Object)} or {@link #get(Object)}
22  * methods can be implemented in terms of the private fields of the host object, or via "setter" and
23  * "getter" methods or by some other mechanism, as appropriate.
24  *
25  * @param <T> The class on which the property is declared.
26  * @param <V> The type that this property represents.
27  */
28 @android.ravenwood.annotation.RavenwoodKeepWholeClass
29 public abstract class Property<T, V> {
30 
31     private final String mName;
32     private final Class<V> mType;
33 
34     /**
35      * This factory method creates and returns a Property given the <code>class</code> and
36      * <code>name</code> parameters, where the <code>"name"</code> parameter represents either:
37      * <ul>
38      *     <li>a public <code>getName()</code> method on the class which takes no arguments, plus an
39      *     optional public <code>setName()</code> method which takes a value of the same type
40      *     returned by <code>getName()</code>
41      *     <li>a public <code>isName()</code> method on the class which takes no arguments, plus an
42      *     optional public <code>setName()</code> method which takes a value of the same type
43      *     returned by <code>isName()</code>
44      *     <li>a public <code>name</code> field on the class
45      * </ul>
46      *
47      * <p>If either of the get/is method alternatives is found on the class, but an appropriate
48      * <code>setName()</code> method is not found, the <code>Property</code> will be
49      * {@link #isReadOnly() readOnly}. Calling the {@link #set(Object, Object)} method on such
50      * a property is allowed, but will have no effect.</p>
51      *
52      * <p>If neither the methods nor the field are found on the class a
53      * {@link NoSuchPropertyException} exception will be thrown.</p>
54      */
of(Class<T> hostType, Class<V> valueType, String name)55     public static <T, V> Property<T, V> of(Class<T> hostType, Class<V> valueType, String name) {
56         return new ReflectiveProperty<T, V>(hostType, valueType, name);
57     }
58 
59     /**
60      * A constructor that takes an identifying name and {@link #getType() type} for the property.
61      */
Property(Class<V> type, String name)62     public Property(Class<V> type, String name) {
63         mName = name;
64         mType = type;
65     }
66 
67     /**
68      * Returns true if the {@link #set(Object, Object)} method does not set the value on the target
69      * object (in which case the {@link #set(Object, Object) set()} method should throw a {@link
70      * NoSuchPropertyException} exception). This may happen if the Property wraps functionality that
71      * allows querying the underlying value but not setting it. For example, the {@link #of(Class,
72      * Class, String)} factory method may return a Property with name "foo" for an object that has
73      * only a <code>getFoo()</code> or <code>isFoo()</code> method, but no matching
74      * <code>setFoo()</code> method.
75      */
isReadOnly()76     public boolean isReadOnly() {
77         return false;
78     }
79 
80     /**
81      * Sets the value on <code>object</code> which this property represents. If the method is unable
82      * to set the value on the target object it will throw an {@link UnsupportedOperationException}
83      * exception.
84      */
set(T object, V value)85     public void set(T object, V value) {
86         throw new UnsupportedOperationException("Property " + getName() +" is read-only");
87     }
88 
89     /**
90      * Returns the current value that this property represents on the given <code>object</code>.
91      */
get(T object)92     public abstract V get(T object);
93 
94     /**
95      * Returns the name for this property.
96      */
getName()97     public String getName() {
98         return mName;
99     }
100 
101     /**
102      * Returns the type for this property.
103      */
getType()104     public Class<V> getType() {
105         return mType;
106     }
107 }
108