JDK泛型中的问号(?)的用途 (泛型集合类的作为参数的时候的继承问题)
(转载自http://www.blogjava.net/dreamstone/archive/2007/02/10/99195.html)
Jdk1.5中支持了泛型,在泛型的使用过程中经常会遇到这样一类问题
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调用的地方
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你会发现编译错误,但是在我们的需求中Child的集合类是可以代替Parent的集合类来使用的,但是因为编译器不认同,因为两个集合类之间 没有直接的继承关系。如何实现呢?在Jdk1.5的Source中我们找到了答案,随便找一个带有泛型的类,点进去可以看到泛型的定义,例如 ArrayList<E> HashMap<K,V> 等等
这里以ArrayList为例:注意addAll这个函数
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ok,明白了,这个就是问号的作用.更改我们的函数
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