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