bf493e3b88
git-svn-id: https://svn.apache.org/repos/asf/poi/branches/ooxml@613951 13f79535-47bb-0310-9956-ffa450edef68
45 lines
1.6 KiB
Plaintext
45 lines
1.6 KiB
Plaintext
Fun with Interfaces
|
|
-------------------
|
|
|
|
Let us consider a simple case
|
|
|
|
public Interface IFoo {}
|
|
public Interface IBar {
|
|
public IFoo getFoo();
|
|
}
|
|
|
|
public class RealFoo implements IFoo {}
|
|
public class RealBar implements IBar {
|
|
public RealFoo getFoo() { return new RealFoo(); }
|
|
}
|
|
|
|
Looks ok, doesn't it? If you access RealBar directly, you get back a
|
|
RealFoo. If you access RealBar via the IBar interface, you get back a
|
|
IFoo object instead. All looks good.
|
|
|
|
Only snag - this doesn't work with any JDK older than 1.5. If you're on
|
|
JDK 1.3 or JDK 1.4, you will get a compile time error about incompatible
|
|
return signatures.
|
|
|
|
|
|
At the moment, we're still committed to having the core of POI work on
|
|
JDK 1.3 / JDK 1.4. If you want the OOXML support, then you need to move
|
|
to JDK 1.5. This allows us a sort of work-around for the problems:
|
|
|
|
JDK 1.3 / JDK 1.4:
|
|
You can't use the OOXML stuff anyway, so you probably don't care about
|
|
the new interfaces
|
|
So, have the existing code (hssf) compile against dummy interfaces, which
|
|
don't actually provide any methods
|
|
You can't then use the interfaces, but you probably didn't want to anyway
|
|
These live in src/ooxml/interfaces-jdk14
|
|
|
|
JDK 1.5:
|
|
Compile the existing code (hssf) against full interfaces. Users can still
|
|
use the concrete HSSF classes if they want, or if they use the interfaces,
|
|
their code will work with the ooxml support too
|
|
Need to change any methods that take a concrete object (eg HSSFCell) to
|
|
take the interface (eg Cell), and cast, otherwise they're not compatible
|
|
with the interface contract (which specifies Cell not HSSFCell).
|
|
These live in src/ooxml/interfaces-jdk15
|