Java泛型 - 将一个子类型的集合传递给一个需要基类型集合的方法 [英] Java generics - passing a collection of subtype to a method requiring a collection of base type
问题描述
如何在Java中执行此操作 - 将一个子类型的集合传递给需要基类型集合的方法?
下面的例子给出了:
方法foo(Map< String,List>)不适用于参数(Map< String,MyList>)
我可以通过为类型化集合创建类层次结构来实现 - 但是否有可能?
public void testStackOverflow(){
$ b $ class MyList extends AbstractList {
public Object get(int index){
返回null;
}
public int size(){
return 0;
}
};
地图< String,List> baseColl = null;
地图< String,MyList> subColl = null;
foo(subColl);
$ b $ private void foo(Map< String,List> in){
}
编辑:从答案中发现,这需要有界通配符,因此添加此文本以便搜索
将 foo
更改为:
private void foo (Map< String,?extends List> in){
}
你可以在 foo
中做什么,但这是合理的。您知道,您从地图中获取的任何值都是一个列表,但您不知道要将哪种值放入地图。
How to do this in Java - passing a collection of subtype to a method requiring a collection of base type?
The example below gives:
The method foo(Map<String,List>) is not applicable for the arguments (Map<String,MyList>)
I can implement by creating a class hierarchy for the typed collections - but is it possible otherwise?
public void testStackOverflow() {
class MyList extends AbstractList {
public Object get(int index) {
return null;
}
public int size() {
return 0;
}
};
Map <String, List> baseColl = null;
Map <String, MyList> subColl = null;
foo (subColl);
}
private void foo (Map <String, List> in) {
}
EDIT: Turns out from the answers that this requires "bounded wildcard" so adding this text for searchability
Change foo
to:
private void foo(Map <String, ? extends List> in) {
}
That will restrict what you can do within foo
, but that's reasonable. You know that any value you fetch from the map will be a list, but you don't know what kind of value is valid to put into the map.
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