How do annotations prevent mutations of an array parameter?
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15
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I understand that annotations are immutable, however, arrays in Java are by themselves not immutable. After running a test I notice that the array returned from an annotation parameter can be mutated but it does not effect the source array:
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@interface ArrayAnnotation {
String value() default {};
}
@ArrayAnnotation({"foo"})
public class Main {
public static void main(String args) {
ArrayAnnotation test = Main.class.getAnnotation(ArrayAnnotation.class);
String test0 = test.value();
test0[0] = "bar";
System.out.println(test0[0]);
String test1 = test.value();
System.out.println(test1[0]);
}
}
This prints:
bar
foo
What is going on behind the scenes here? Is there simply an array copy happening during each call to value(), or is it something more complex?
java arrays annotations immutability
asked Nov 22 at 18:59
flakes
6,51311850
add a comment |
up vote
15
down vote
favorite
I understand that annotations are immutable, however, arrays in Java are by themselves not immutable. After running a test I notice that the array returned from an annotation parameter can be mutated but it does not effect the source array:
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@interface ArrayAnnotation {
String value() default {};
}
@ArrayAnnotation({"foo"})
public class Main {
public static void main(String args) {
ArrayAnnotation test = Main.class.getAnnotation(ArrayAnnotation.class);
String test0 = test.value();
test0[0] = "bar";
System.out.println(test0[0]);
String test1 = test.value();
System.out.println(test1[0]);
}
}
This prints:
bar
foo
What is going on behind the scenes here? Is there simply an array copy happening during each call to value(), or is it something more complex?
java arrays annotations immutability
asked Nov 22 at 18:59
flakes
6,51311850
add a comment |
up vote
15
down vote
favorite
up vote
15
down vote
favorite
I understand that annotations are immutable, however, arrays in Java are by themselves not immutable. After running a test I notice that the array returned from an annotation parameter can be mutated but it does not effect the source array:
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@interface ArrayAnnotation {
String value() default {};
}
@ArrayAnnotation({"foo"})
public class Main {
public static void main(String args) {
ArrayAnnotation test = Main.class.getAnnotation(ArrayAnnotation.class);
String test0 = test.value();
test0[0] = "bar";
System.out.println(test0[0]);
String test1 = test.value();
System.out.println(test1[0]);
}
}
This prints:
bar
foo
What is going on behind the scenes here? Is there simply an array copy happening during each call to value(), or is it something more complex?
java arrays annotations immutability
asked Nov 22 at 18:59
flakes
6,51311850
I understand that annotations are immutable, however, arrays in Java are by themselves not immutable. After running a test I notice that the array returned from an annotation parameter can be mutated but it does not effect the source array:
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@interface ArrayAnnotation {
String value() default {};
}
@ArrayAnnotation({"foo"})
public class Main {
public static void main(String args) {
ArrayAnnotation test = Main.class.getAnnotation(ArrayAnnotation.class);
String test0 = test.value();
test0[0] = "bar";
System.out.println(test0[0]);
String test1 = test.value();
System.out.println(test1[0]);
}
}
This prints:
bar
foo
What is going on behind the scenes here? Is there simply an array copy happening during each call to value(), or is it something more complex?
java arrays annotations immutability
java arrays annotations immutability
asked Nov 22 at 18:59
flakes
6,51311850
asked Nov 22 at 18:59
flakes
6,51311850
edited Nov 22 at 19:05
asked Nov 22 at 18:59
flakes
6,51311850
asked Nov 22 at 18:59
flakes
6,51311850
asked Nov 22 at 18:59
flakes
6,51311850
6,51311850
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
up vote
13
down vote
accepted
Is there simply an array copy happening during each call to value(), or is it something more complex?
Yes, the array is copied.
Annotations are a special kind of interface type. (JLS)
They are implemented by some Proxy classes at runtime.
You can debug it if you set breakpoint at Proxy.newProxyInstance().
Invocations on annotation are intercepted by AnnotationInvocationHandler which copies arrays:
if (result.getClass().isArray() && Array.getLength(result) != 0)
result = cloneArray(result);
answered Nov 22 at 19:17
caco3
1,0171417
1
Ah, very cool! The step-into feature in my IDE's debugger wasn't triggering anything forvalues()but adding a breakpoint directly in theAnnotationInvocationHandlerproxy does the trick! Thanks a lot!
– flakes
Nov 22 at 19:23
add a comment |
up vote
5
down vote
You are right, it returns a copy each time to ensure it is not changed.
In a future version of Java, this copy might be optimised away.
answered Nov 22 at 19:16
Peter Lawrey
439k55557958
Yeah, I was thinking that it seems pretty expensive to copy the array every time that it is viewed!
– flakes
Nov 22 at 19:24
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
13
down vote
accepted
Is there simply an array copy happening during each call to value(), or is it something more complex?
Yes, the array is copied.
Annotations are a special kind of interface type. (JLS)
They are implemented by some Proxy classes at runtime.
You can debug it if you set breakpoint at Proxy.newProxyInstance().
Invocations on annotation are intercepted by AnnotationInvocationHandler which copies arrays:
if (result.getClass().isArray() && Array.getLength(result) != 0)
result = cloneArray(result);
answered Nov 22 at 19:17
caco3
1,0171417
1
Ah, very cool! The step-into feature in my IDE's debugger wasn't triggering anything forvalues()but adding a breakpoint directly in theAnnotationInvocationHandlerproxy does the trick! Thanks a lot!
– flakes
Nov 22 at 19:23
add a comment |
up vote
13
down vote
accepted
Is there simply an array copy happening during each call to value(), or is it something more complex?
Yes, the array is copied.
Annotations are a special kind of interface type. (JLS)
They are implemented by some Proxy classes at runtime.
You can debug it if you set breakpoint at Proxy.newProxyInstance().
Invocations on annotation are intercepted by AnnotationInvocationHandler which copies arrays:
if (result.getClass().isArray() && Array.getLength(result) != 0)
result = cloneArray(result);
answered Nov 22 at 19:17
caco3
1,0171417
1
Ah, very cool! The step-into feature in my IDE's debugger wasn't triggering anything forvalues()but adding a breakpoint directly in theAnnotationInvocationHandlerproxy does the trick! Thanks a lot!
– flakes
Nov 22 at 19:23
add a comment |
up vote
13
down vote
accepted
up vote
13
down vote
accepted
Is there simply an array copy happening during each call to value(), or is it something more complex?
Yes, the array is copied.
Annotations are a special kind of interface type. (JLS)
They are implemented by some Proxy classes at runtime.
You can debug it if you set breakpoint at Proxy.newProxyInstance().
Invocations on annotation are intercepted by AnnotationInvocationHandler which copies arrays:
if (result.getClass().isArray() && Array.getLength(result) != 0)
result = cloneArray(result);
answered Nov 22 at 19:17
caco3
1,0171417
Is there simply an array copy happening during each call to value(), or is it something more complex?
Yes, the array is copied.
Annotations are a special kind of interface type. (JLS)
They are implemented by some Proxy classes at runtime.
You can debug it if you set breakpoint at Proxy.newProxyInstance().
Invocations on annotation are intercepted by AnnotationInvocationHandler which copies arrays:
if (result.getClass().isArray() && Array.getLength(result) != 0)
result = cloneArray(result);
answered Nov 22 at 19:17
caco3
1,0171417
answered Nov 22 at 19:17
caco3
1,0171417
answered Nov 22 at 19:17
caco3
1,0171417
answered Nov 22 at 19:17
caco3
1,0171417
1,0171417
1
Ah, very cool! The step-into feature in my IDE's debugger wasn't triggering anything forvalues()but adding a breakpoint directly in theAnnotationInvocationHandlerproxy does the trick! Thanks a lot!
– flakes
Nov 22 at 19:23
add a comment |
1
Ah, very cool! The step-into feature in my IDE's debugger wasn't triggering anything forvalues()but adding a breakpoint directly in theAnnotationInvocationHandlerproxy does the trick! Thanks a lot!
– flakes
Nov 22 at 19:23
1
1
Ah, very cool! The step-into feature in my IDE's debugger wasn't triggering anything for
values() but adding a breakpoint directly in the AnnotationInvocationHandler proxy does the trick! Thanks a lot!– flakes
Nov 22 at 19:23
Ah, very cool! The step-into feature in my IDE's debugger wasn't triggering anything for
values() but adding a breakpoint directly in the AnnotationInvocationHandler proxy does the trick! Thanks a lot!– flakes
Nov 22 at 19:23
add a comment |
up vote
5
down vote
You are right, it returns a copy each time to ensure it is not changed.
In a future version of Java, this copy might be optimised away.
answered Nov 22 at 19:16
Peter Lawrey
439k55557958
Yeah, I was thinking that it seems pretty expensive to copy the array every time that it is viewed!
– flakes
Nov 22 at 19:24
add a comment |
up vote
5
down vote
You are right, it returns a copy each time to ensure it is not changed.
In a future version of Java, this copy might be optimised away.
answered Nov 22 at 19:16
Peter Lawrey
439k55557958
Yeah, I was thinking that it seems pretty expensive to copy the array every time that it is viewed!
– flakes
Nov 22 at 19:24
add a comment |
up vote
5
down vote
up vote
5
down vote
You are right, it returns a copy each time to ensure it is not changed.
In a future version of Java, this copy might be optimised away.
answered Nov 22 at 19:16
Peter Lawrey
439k55557958
You are right, it returns a copy each time to ensure it is not changed.
In a future version of Java, this copy might be optimised away.
answered Nov 22 at 19:16
Peter Lawrey
439k55557958
answered Nov 22 at 19:16
Peter Lawrey
439k55557958
answered Nov 22 at 19:16
Peter Lawrey
439k55557958
answered Nov 22 at 19:16
Peter Lawrey
439k55557958
439k55557958
Yeah, I was thinking that it seems pretty expensive to copy the array every time that it is viewed!
– flakes
Nov 22 at 19:24
add a comment |
Yeah, I was thinking that it seems pretty expensive to copy the array every time that it is viewed!
– flakes
Nov 22 at 19:24
Yeah, I was thinking that it seems pretty expensive to copy the array every time that it is viewed!
– flakes
Nov 22 at 19:24
Yeah, I was thinking that it seems pretty expensive to copy the array every time that it is viewed!
– flakes
Nov 22 at 19:24
add a comment |
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