| ←Older revision | Revision as of 15:31, 14 July 2016 | ||
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More info at [[Covariance]]. For possible trick around this behavior see [[Erasure]]. | More info at [[Covariance]]. For possible trick around this behavior see [[Erasure]]. | ||
| + | |||
| + | [[Category:APIDesignPatterns]] | ||
| + | [[Category:APIDesignPatterns:Evolution]] | ||
| ←Older revision | Revision as of 09:21, 13 December 2011 | ||
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<source lang="java" snippet="variance.contravariance.v2"/> | <source lang="java" snippet="variance.contravariance.v2"/> | ||
| - | Existing code would compile against the new library. However because the rules for looking up the right method are different between [[JavaC]] and [[JVM]] | + | Existing code would compile against the new library. However because the rules for looking up the right method are different between [[JavaC]] and [[JVM]], we'll have a problem. Code like this will compile fine, but... |
<source lang="java" snippet="variance.contravariance.test"/> | <source lang="java" snippet="variance.contravariance.test"/> | ||
| - | + | ...if compiled against version 1.0 and executed against version 2.0, it will throw linkage errors: | |
<source lang="bash"> | <source lang="bash"> | ||
| ←Older revision | Revision as of 17:33, 19 October 2011 | ||
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| - | Everything one would ever like to know about [[Covariance]] and [[Contravariance]] is available at [[wikipedia:Covariance_and_contravariance_(computer_science)|wikipedia]]. Here is just a small example how it does not work in [[Java]]. | + | Everything one would ever like to know about [[Covariance]] and [[Contravariance]] is available at [[wikipedia:Covariance_and_contravariance_(computer_science)|wikipedia]]. Here is just a small example how it does not work in [[Java]] (the argumentation is the same as in case of [[Covariance]]). First version would like to be fixed: |
| - | [[ | + | <source lang="java" snippet="variance.contravariance.v1"/> |
| + | |||
| + | However when one tries to change the parameter type: | ||
| + | |||
| + | <source lang="java" snippet="variance.contravariance.v2"/> | ||
| + | |||
| + | Existing code would compile against the new library. However because the rules for looking up the right method are different between [[JavaC]] and [[JVM]] code like following will have problems: | ||
| + | |||
| + | <source lang="java" snippet="variance.contravariance.test"/> | ||
| + | |||
| + | If compiled against version 1.0 and executed against version 2.0, it will throw linkage errors: | ||
| + | |||
| + | <source lang="bash"> | ||
| + | Mixing should not work: Compiling with version 1.0 and running against version 2.0 fails. | ||
| + | Exception in thread "main" java.lang.NoSuchMethodError: api.Contravariance.isPositive(Ljava/lang/Integer;)Z | ||
| + | at test.ContravarianceTest.main(Unknown Source) | ||
| + | Java Result: 1 | ||
| + | </source> | ||
| + | |||
| + | More info at [[Covariance]]. For possible trick around this behavior see [[Erasure]]. | ||
New page: Everything one would ever like to know about Covariance and Contravariance is available at wikipedia. Here is just a ...
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