如何在运行时告知Java 1.4类型或成员已弃用？

Question

In Java 6 I can use a technique like this:

@Deprecated
public final class Test {

    public static void main(String[] args) {
        System.out.println(Test.class.isAnnotationPresent(Deprecated.class));
    }   
}

to decide if a type is deprecated. Is there any way at all to do this in 1.4 with the old style (Javadoc-based) deprecation?

Answer 1

You can't make such a check on javadoc tags. Well, you can, if you distribute your source code, load the source file and parse it for the @deprecated tag, but this is not preferable.

The pre-Java5 way of indicating something is by using a marker interface. You can define your own:

public interface Deprecated {
}

and make deprecated classes implement it. You cannot use it on methods, of course.

public final class Test implements Deprecated

And then check whether Deprecated.class.isAssignableFrom(Test.class) .

But deprecation is a purely indicative notion and should not be used at run-time to differentiate behaviour.

Answer 2

没有，因为JavaDoc是一个注释，因此在运行时不可用。

Answer 3

The @deprecated tag is only used by the compiler but not put in the compiled java byte code, so you cannot detect it after compilation.

What is it you want to do?

Answer 4

Actually, you can.

The same pre-1.5 source code, compiled with or without the @deprecated JavaDoc tag, produces class files which differ in a couple of bytes:

00000000  ca fe ba be 00 00 00 34  00 0a 07 00 02 01 00 02  |.......4........|
00000010  43 30 07 00 04 01 00 10  6a 61 76 61 2f 6c 61 6e  |C0......java/lan|
00000020  67 2f 4f 62 6a 65 63 74  01 00 06 3c 69 6e 69 74  |g/Object...<init|
00000030  3e 01 00 03 28 29 56 01  00 04 43 6f 64 65 0a 00  |>...()V...Code..|
00000040  03 00 09 0c 00 05 00 06  00 20 00 01 00 03 00 00  |......... ......|
00000050  00 00 00 01 00 00 00 05  00 06 00 01 00 07 00 00  |................|
00000060  00 11 00 01 00 01 00 00  00 05 2a b7 00 08 b1 00  |..........*.....|
00000070  00 00 00 00 00                                    |.....|

vs

00000000  ca fe ba be 00 00 00 34  00 0b 07 00 02 01 00 02  |.......4........|
00000010  43 30 07 00 04 01 00 10  6a 61 76 61 2f 6c 61 6e  |C0......java/lan|
00000020  67 2f 4f 62 6a 65 63 74  01 00 06 3c 69 6e 69 74  |g/Object...<init|
00000030  3e 01 00 03 28 29 56 01  00 04 43 6f 64 65 0a 00  |>...()V...Code..|
00000040  03 00 09 0c 00 05 00 06  01 00 0a 44 65 70 72 65  |...........Depre|
00000050  63 61 74 65 64 00 20 00  01 00 03 00 00 00 00 00  |cated. .........|
00000060  01 00 00 00 05 00 06 00  01 00 07 00 00 00 11 00  |................|
00000070  01 00 01 00 00 00 05 2a  b7 00 08 b1 00 00 00 00  |.......*........|
00000080  00 01 00 0a 00 00 00 00                           |........|

If you take a look at the JVM Specification, Chapter 4 , there's a Deprecated attribute ( §4.7.15 ) in the ClassFile structure.

There're tools capable to determine whether a class is deprecated or not:

• any of the modern IDEs
• jad (the Java decompiler), closed source, purely native code.
• jclasslib project (GPLv2) by Ingo Kegel .

You can either go ahead and implement the ClassFile structure yourself or, if you have nothing against GPLv2, take a look at org.gjt.jclasslib.structures.AttributeInfo class.

Answer 5

注释从版本1.5开始可用，因此1.4和之前的版本不可用