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5 <title>javafx.beans.binding</title>
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8 <h1>Characteristics of Bindings</h1>
9 <p>Bindings are assembled from one or more sources, usually called
10 their dependencies. A binding observes its dependencies for changes
11 and updates its own value according to changes in the dependencies.</p>
12 <p>Almost all bindings defined in this library require
13 implementations of {@link javafx.beans.Observable} for their
14 dependencies. There are two types of implementations already provided,
15 the properties in the package {@link javafx.beans.property} and the
16 observable collections ({@link javafx.collections.ObservableList} and
17 {@link javafx.collections.ObservableMap}). Bindings also implement
18 {@code Observable} and can again serve as sources for other bindings
19 allowing to construct very complex bindings from simple ones.</p>
20 <p>Bindings in our implementation are always calculated lazily.
21 That means, if a dependency changes, the result of a binding is not
22 immediately recalculated, but it is marked as invalid. Next time the
23 value of an invalid binding is requested, it is recalculated.</p>
24 <h1>High Level API and Low Level API</h1>
25 <p>The Binding API is roughly divided in two parts, the High Level
26 Binding API and the Low Level Binding API. The High Level Binding API
27 allows to construct simple bindings in an easy to use fashion.
28 Defining a binding with the High Level API should be straightforward,
29 especially when used in an IDE that provides code completion.
30 Unfortunately it has its limitation and at that point the Low Level
31 API comes into play. Experienced Java developers can use the Low Level
32 API to define bindings, if the functionality of the High Level API is
33 not sufficient or to improve the performance. The main goals of the
34 Low Level API are fast execution and small memory footprint.</p>
35 <p>Following is an example of how both APIs can be used. Assuming
36 we have four instances of {@link
37 javafx.beans.property.DoubleProperty} {@code a}, {@code b}, {@code
38 c} , and {@code d}, we can define a binding that calculates {@code a*b
39 + c*d} with the High Level API for example like this:</p>
40 <p>{@code NumberBinding result = Bindings.add (a.multiply(b),
41 c.multiply(d)); }</p>
42 <p>Defining the same binding using the Low Level API could be done
43 like this:</p>
44 <pre>
45 <code>
46 DoubleBinding foo = new DoubleBinding() {
47
48 {
49 super.bind(a, b, c, d);
50 }
51
52 @Override
53 protected double computeValue() {
54 return a.getValue() * b.getValue() + c.getValue() * d.getValue();
55 }
56 };
57 </code>
58 </pre>
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