Analysis of Android Support Library Annotations framework in the Java class library

Android Support Library Annotations is a commonly used tool library in Android development, which provides a technology that uses annotations in the Java library.This article will analyze the technical principles of Android Support Library Annotations and provide some Java code examples. Android SUPPORT LIBARARY AnNotations, as an annotation library, is mainly used to add annotations to the Java class and methods to provide additional auxiliary information or functions.It marks the special places in the Java code by annotating, so that developers can use and understand these code more conveniently. The technical principles of Android SUPPORT LIBRARY Annotation's framework mainly include the following aspects: 1. RMB Note: Android SUPPORT LIBRARY Annotations define some meta -annotations to modify other annotations.The role of meta annotations is the behavior and usage method of specified annotations. For example, the @RETENTION annotation is used to specify the retention strategy of the annotation, and the@Target annotation is used to specify the scope of the annotation. 2. Note processor: Android Support Library Annotations also provides an annotation processor for processing the annotation during compilation.The annotation processor can generate additional code or perform other operations according to the definition and marking position of the annotation.For example, auxiliary code can be generated according to the scrapped class to help developers use this class more conveniently. 3. Support Library: Android Support Library Annotations framework itself depends on the Android Support library.The library provides some general classes and methods to assist the logic related to the annotation.Through the introduction of this library, developers can more easily use the annotations and functions provided by Android Support Library Annotations. Here are some examples of Java code for Java code using Android Support Library Annotations: // Use the @NONNULL annotation marker method parameter must not be null public void foo(@NonNull String param) { // Operate Param } // Use the @NULLABLE annotation marker method to return the value can be NULL @Nullable public String bar() { // Return a string return null; } // Use @StringDef to define an annotation, limit one of the string constants defined by the parameter as defined @StringDef({COLOR_RED, COLOR_GREEN, COLOR_BLUE}) @Retention(RetentionPolicy.SOURCE) public @interface Color {} public void setColor(@Color String color) { // Set color } In the above code example, the@Nonnull annotation is used for the marking method parameters cannot be NULL,@nullable annotation is used to marked the method return value,@stringDef annotation is used to limit the number of string constants specified as specified.These annotations can improve the readability and robustness of the code, and can also perform some additional logic processing through the annotation processor during the compilation period. In summary, Android Support Library Annotations framework adds additional auxiliary information and functions to the Java library through annotations.Its technical principles mainly include the use of meta -injection modification and solution, the annotation processor processing the annotation, and the relevant class and methods that depend on the Android Support library.Developers can improve the readability and robustness of the code by using Android Support Library Annotations, and add some additional auxiliary functions.