问题描述
来自 Java 文档:
From the Java doc:
类:注释将由编译器记录在类文件中，但不需要在运行时由 VM 保留.
CLASS: Annotations are to be recorded in the class file by the compiler but need not be retained by the VM at run time.
运行时间:注释将由编译器记录在类文件中，并在运行时由 VM 保留，因此可以反射性地读取它们.
RUNTIME: Annotations are to be recorded in the class file by the compiler and retained by the VM at run time, so they may be read reflectively.
来源:注释将被编译器丢弃.
SOURCE: Annotations are to be discarded by the compiler.
我了解 RUNTIME(为了使用带反射的注解)和 CLASS(对于编译器)的用法，但我不明白什么时候可以使用
I understand the usages of RUNTIME (in order to use annotation with reflection) and CLASS (for the compiler) but I don't understand when it can be usefull to use
@Retention(RetentionPolicy.SOURCE)
@Retention(RetentionPolicy.SOURCE)
你能解释一下吗?
推荐答案
像@SuppressWarnings、@Override 这样的东西是编译器使用的注解——在运行时不需要.对于那些 RetentionPolicy.SOURCE 是有意义的.注释也可用于生成代码(查看 Spring ROO)——在运行时也不需要此类注释.
Things like @SuppressWarnings, @Override are annotations used by the compiler - not needed at runtime. For those RetentionPolicy.SOURCE would make sense. Also annotations can be used to generate code (look at Spring ROO) - such annotation are also not required at run time.
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