-
Bug
-
Resolution: Cannot Reproduce
-
P3
-
None
-
8u45
-
x86
-
windows_8
FULL PRODUCT VERSION :
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.3.9600]
A DESCRIPTION OF THE PROBLEM :
There is a certain kind of generic type inference that no longer works with Java 8 compilers.
REGRESSION. Last worked in version 7u76
ADDITIONAL REGRESSION INFORMATION:
java version "1.7.0_67"
Java(TM) SE Runtime Environment (build 1.7.0_67-b01)
Java HotSpot(TM) 64-Bit Server VM (build 24.65-b04, mixed mode)
STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
javac fails to compile the following code
--------------------------------------------
import java.util.List;
public class Test {
static final void a(Class<? extends List<?>> type) {
b(newList(type));
}
static final <T> List<T> b(List<T> list) {
return list;
}
static final <L extends List<?>> L newList(Class<L> type) {
try {
return type.newInstance();
}
catch (Exception e) {
throw new RuntimeException(e);
}
}
}
EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The above program should compile
ACTUAL -
A compilation error
ERROR MESSAGES/STACK TRACES THAT OCCUR :
Test.java:5: error: method b in class Test cannot be applied to given types;
b(newList(type));
^
required: List<T>
found: CAP#1
reason: inference variable L has incompatible bounds
equality constraints: CAP#2
upper bounds: List<CAP#3>,List<?>
where T,L are type-variables:
T extends Object declared in method <T>b(List<T>)
L extends List<?> declared in method <L>newList(Class<L>)
where CAP#1,CAP#2,CAP#3 are fresh type-variables:
CAP#1 extends List<?> from capture of ? extends List<?>
CAP#2 extends List<?> from capture of ? extends List<?>
CAP#3 extends Object from capture of ?
1 error
REPRODUCIBILITY :
This bug can be reproduced always.
---------- BEGIN SOURCE ----------
See above
---------- END SOURCE ----------
CUSTOMER SUBMITTED WORKAROUND :
Assign the argument to b() to a local variable to prevent the need for type inference.
--------------------------------------------
import java.util.List;
public class Test {
static final void a(Class<? extends List<?>> type) {
List<?> list = newList(type);
b(list);
}
static final <T> List<T> b(List<T> list) {
return list;
}
static final <L extends List<?>> L newList(Class<L> type) {
try {
return type.newInstance();
}
catch (Exception e) {
throw new RuntimeException(e);
}
}
}
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.3.9600]
A DESCRIPTION OF THE PROBLEM :
There is a certain kind of generic type inference that no longer works with Java 8 compilers.
REGRESSION. Last worked in version 7u76
ADDITIONAL REGRESSION INFORMATION:
java version "1.7.0_67"
Java(TM) SE Runtime Environment (build 1.7.0_67-b01)
Java HotSpot(TM) 64-Bit Server VM (build 24.65-b04, mixed mode)
STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
javac fails to compile the following code
--------------------------------------------
import java.util.List;
public class Test {
static final void a(Class<? extends List<?>> type) {
b(newList(type));
}
static final <T> List<T> b(List<T> list) {
return list;
}
static final <L extends List<?>> L newList(Class<L> type) {
try {
return type.newInstance();
}
catch (Exception e) {
throw new RuntimeException(e);
}
}
}
EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The above program should compile
ACTUAL -
A compilation error
ERROR MESSAGES/STACK TRACES THAT OCCUR :
Test.java:5: error: method b in class Test cannot be applied to given types;
b(newList(type));
^
required: List<T>
found: CAP#1
reason: inference variable L has incompatible bounds
equality constraints: CAP#2
upper bounds: List<CAP#3>,List<?>
where T,L are type-variables:
T extends Object declared in method <T>b(List<T>)
L extends List<?> declared in method <L>newList(Class<L>)
where CAP#1,CAP#2,CAP#3 are fresh type-variables:
CAP#1 extends List<?> from capture of ? extends List<?>
CAP#2 extends List<?> from capture of ? extends List<?>
CAP#3 extends Object from capture of ?
1 error
REPRODUCIBILITY :
This bug can be reproduced always.
---------- BEGIN SOURCE ----------
See above
---------- END SOURCE ----------
CUSTOMER SUBMITTED WORKAROUND :
Assign the argument to b() to a local variable to prevent the need for type inference.
--------------------------------------------
import java.util.List;
public class Test {
static final void a(Class<? extends List<?>> type) {
List<?> list = newList(type);
b(list);
}
static final <T> List<T> b(List<T> list) {
return list;
}
static final <L extends List<?>> L newList(Class<L> type) {
try {
return type.newInstance();
}
catch (Exception e) {
throw new RuntimeException(e);
}
}
}
- relates to
-
JDK-8043926 javac, code valid in 7 is not compiling for 8
- Closed