通过反射访问Java静态最终变量值 [英] Accessing Java static final variable value through reflection
问题描述
可以通过反射检索Java静态最终类变量的值吗?
Can the value of a Java static final class variable be retrieved through reflection?
推荐答案
我猜这个它取决于类型和编译器(第二个想法,它最好不要!)。 Sun的编译器内联了原始常量,但我不知道它们是否完全从类中删除了该条目。我会发现。
I would guess that it depends on the type and the compiler (on second thought, it had sure better not!). Sun's compiler inlines primitive constants, but I don't know if they remove the entry from the class entirely. I'll find out.
编辑是的,即使内联它们,您仍然可以访问它们。测试类:
Yes, you can still access them even if they are inlined. Test class:
public class ReflectionConstantTest {
private static final int CONST_INT = 100;
private static final String CONST_STRING = "String";
private static final Object CONST_OBJECT = new StringBuilder("xyz");
public static void main(String[] args) throws Exception {
int testInt = CONST_INT;
String testString = CONST_STRING;
Object testObj = CONST_OBJECT;
for (Field f : ReflectionConstantTest.class.getDeclaredFields()) {
f.setAccessible(true);
System.out.println(f.getName() + ": " + f.get(null));
}
}
}
输出:
CONST_INT: 100
CONST_STRING: String
CONST_OBJECT: xyz
javap -c
输出:
Compiled from "ReflectionConstantTest.java"
public class scratch.ReflectionConstantTest extends java.lang.Object{
public scratch.ReflectionConstantTest();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."":()V
4: return
public static void main(java.lang.String[]) throws java.lang.Exception;
Code:
0: bipush 100
2: istore_1
3: ldc #2; //String String
5: astore_2
6: getstatic #3; //Field CONST_OBJECT:Ljava/lang/Object;
9: astore_3
10: ldc_w #4; //class scratch/ReflectionConstantTest
13: invokevirtual #5; //Method java/lang/Class.getDeclaredFields:()[Ljava/lang/reflect/Field;
16: astore 4
18: aload 4
20: arraylength
21: istore 5
23: iconst_0
24: istore 6
26: iload 6
28: iload 5
30: if_icmpge 90
33: aload 4
35: iload 6
37: aaload
38: astore 7
40: aload 7
42: iconst_1
43: invokevirtual #6; //Method java/lang/reflect/Field.setAccessible:(Z)V
46: getstatic #7; //Field java/lang/System.out:Ljava/io/PrintStream;
49: new #8; //class java/lang/StringBuilder
52: dup
53: invokespecial #9; //Method java/lang/StringBuilder."":()V
56: aload 7
58: invokevirtual #10; //Method java/lang/reflect/Field.getName:()Ljava/lang/String;
61: invokevirtual #11; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
64: ldc #12; //String :
66: invokevirtual #11; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
69: aload 7
71: aconst_null
72: invokevirtual #13; //Method java/lang/reflect/Field.get:(Ljava/lang/Object;)Ljava/lang/Object;
75: invokevirtual #14; //Method java/lang/StringBuilder.append:(Ljava/lang/Object;)Ljava/lang/StringBuilder;
78: invokevirtual #15; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
81: invokevirtual #16; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
84: iinc 6, 1
87: goto 26
90: return
static {};
Code:
0: new #8; //class java/lang/StringBuilder
3: dup
4: ldc #17; //String xyz
6: invokespecial #18; //Method java/lang/StringBuilder."":(Ljava/lang/String;)V
9: putstatic #3; //Field CONST_OBJECT:Ljava/lang/Object;
12: return
}
你可以看到 CONST_INT
是内联的,但 CONST_STRING
和 CONST_OBJECT
(当然)不是。然而 CONST_INT
仍然可以反映。
You can see that CONST_INT
is inlined, but CONST_STRING
and CONST_OBJECT
(of course) are not. Yet CONST_INT
is still available reflectively.
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