I have faced a weird issue while using generics (on JDK 1.5.0 update 3 for Windows).

Consider the following simple example.

public class Foo { 
     public class FooInner<T> {  }
     public <T> FooInner<T> getInner() { return null; }
}
 
 
public class Bar  {
  final Foo foo=new Foo();  
  
  public Foo.FooInner<Void> i1=foo.getInner(); // incompatible types error on separate compilation
  public Foo.FooInner<Long> i2=foo.<Long>getInner(); // incompatible types error on separate compilation
}




If I compile the both files together

$ javac Foo.java Bar.java

they are compiled fine without any errors or warnings (exactly as I expect).

However, if I then compile just Bar.java

$ javac Bar.java

I get the following errors:



Bar.java:4: incompatible types; no instance(s) of type variable(s) T exist so that Foo.FooInner<T> conforms to Foo.FooInner<java.lang.Void>
found : <T>Foo.FooInner<T>
required: Foo.FooInner<java.lang.Void>
public Foo.FooInner<Void> i1=foo.getInner();
^
Bar.java:5: incompatible types
found : Foo.FooInner<java.lang.Long>
required: Foo.FooInner<java.lang.Long>
public Foo.FooInner<Long> i2=foo.<Long>getInner();
^