Generic method call in Eclipse - eclipse

Question

Tried to run a project in IDEA and got an exception. Before that project was always run on Eclipse only.
Here is the example code:
package com.test;
public class GenericMethod {
private Object value;
#SuppressWarnings("unchecked")
public <X> X getValue() {
return (X) value;
}
public void setValue(Object value) {
this.value = value;
}
}
And the class that uses it:
package com.test;
public class GenericMethodTest {
public static void main(String[] args) {
GenericMethod method = new GenericMethod();
method.setValue(3);
int[] array = new int[] {1, 2};
array[0] = method.getValue();
System.out.println(array[0]);
}
}
So if you try to run this example in Eclipse - everything works fine. It compiles and shows you correct result.
But if you try to run it, say, in IDEA or if you just use ant or your console and javac command - you'll get compile error:
Buildfile: C:\test\build.xml
build:
[javac] C:\test\build.xml:13: warning: 'includeantruntime' was not set, defaulting to build.sysclasspath=last; set to false for repeatable builds
[javac] Compiling 1 source file to C:\test\bin
[javac] C:\test\src\com\test\GenericMethodTest.java:15: type parameters of <X>X cannot be determined; no unique maximal instance exists for type variable X with upper bounds int,java.lang.Object
[javac] array[0] = method.getValue();
[javac] ^
[javac] 1 error
What's happening?
Does Eclipse use it's own compiler?
Who has a bug?

Answer 1

In this case the code you posted has the bug. Eclipse let it slide (because you told it too with the #SuppressWarnings("unchecked")), but IDEA doesn't appear to be so forgiving. You can't cast value to X, because because of erasure you don't know what X is at runtime.
The proper way to do this would be to generify the class, and then store value as type X.
public class GenericMethod<X> {
private X value;
public X getValue() {
return value;
}
public void setValue(X value) {
this.value = value;
}
}
If you can't do that, then don't try to use generics here, just cast. Of course, if you were really really keen to use generics, you could also do something like this:
public <X> X getValue(Class<X> clazz) {
return clazz.cast(value);
}
But you'd have to have the class.