在静态初始化程序中将子类添加到超类型的ConcurrentHashMap中？ [英] Add subclasses to ConcurrentHashMap of super type in a static initializer?

问题描述

  public class People {
 
 class Family extends People {
 
} 
 
} 
 
 
 public class Together {
 private static Collection< Family> familyList = new ArrayList< Family>（）; 
 private static ConcurrentMap< String，Collection< People>> registry = new ConcurrentHashMap< String，Collection< People>>（）; 
 
 static {
 registry.put（Family.class.toString（），familyList）; 
 
 
 $ / code $ / pre 
 
 
错误信息：
 
 
 方法put（String，Collection< people>）类型为Map< String，Collection< people>>不适用于参数（String，Collection< family>）
  
为什么我不能把 familyList 到注册表？我认为，因为 family 扩展了 people ，所以我应该能够将子类型放入超类型 registry 。
 
 
 
编辑：上面已解决。这个问题的最后一部分涉及到一个更复杂的例子：
 
 
  public class Together {
 private static ConcurrentMap< String，Collection< Family>> familyMap = new ConcurrentHashMap< String，Collection< Family>>（）; 
 private static ConcurrentMap< String，ConcurrentMap< String，Collection< People>>> registry2 = new ConcurrentHashMap< String，ConcurrentMap< String，Collection< People>>>（）; 
 
 static {
 registry2.put（Family.class.toString（），familyMap）; 
 
 
 $ / code $ / pre 
 
 
（我已经试过改变 registry2 具有？extends People  
 
 
 
现在错误是：
 类型Map< String，ConcurrentMap< String，Collection< People>>中的方法put（String，ConcurrentMap< String，Collection< People>>）不适用于（String，ConcurrentMap< String，Collection< Family>>）  试试这个： 
 
 
 
  people.java   
 
  public class people {
 
 public class family extends people {
 
} 
 
 public static void main（String [] args）{
 together t = new together（）; 
 System.out.println（together.registry）; 
} 
 
} 
  
  together.java   
 
 
  import java.util.ArrayList; 
 import java.util.C ollection; 
 import java.util.concurrent.ConcurrentHashMap; 
 import java.util.concurrent.ConcurrentMap; 
 
公共课程{b $ b private static Collection< people.family> familyList = new ArrayList< people.family>（）; 
 public static ConcurrentMap< String，Collection< ;?扩展人员>> registry = new ConcurrentHashMap< String，Collection <？扩展人员>>（）; 
 
 static {
 registry.put（people.family.class.toString（），familyList）; 
} 
 
} 
  
 
public class People {

    class Family extends People {

    }

}


public class Together {
    private static Collection<Family> familyList = new ArrayList<Family>();
    private static ConcurrentMap<String, Collection<People>> registry = new ConcurrentHashMap<String, Collection<People>>();

    static {
        registry.put(Family.class.toString(), familyList); 
    }
}
Error message:
The method put(String, Collection<people>) in the type Map<String,Collection<people>> is not applicable for the arguments (String, Collection<family>)
Why can't I put familyList into registry?  I figure that since family extendspeople that i should be able to place the sub types into the super type registry .


EDIT:  The above is solved.  My last part of the question involves a more complicated example using the same names:
public class Together {
    private static ConcurrentMap<String, Collection<Family>> familyMap= new ConcurrentHashMap<String, Collection<Family>>();
    private static ConcurrentMap<String, ConcurrentMap<String, Collection<People>>> registry2 = new ConcurrentHashMap<String, ConcurrentMap<String, Collection<People>>>();

    static {
        registry2.put(Family.class.toString(), familyMap); 
    }
}
(I already tried changing the declaration of registry2 to having ?extends People

Now the error is:
The method put(String, ConcurrentMap<String,Collection<People>>) in the type Map<String,ConcurrentMap<String,Collection<People>>> is not applicable for the arguments (String, ConcurrentMap<String,Collection<Family>>)
解决方案
Try this:

people.java
public class people {

    public class family extends people {

    }

    public static void main(String[] args) {
        together t = new together();
        System.out.println(together.registry);
    }

}
together.java
import java.util.ArrayList;
import java.util.Collection;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

public class together {
    private static Collection<people.family> familyList = new ArrayList<people.family>();
    public static ConcurrentMap<String, Collection<? extends people>> registry = new ConcurrentHashMap<String, Collection<? extends people>>();

    static {
        registry.put(people.family.class.toString(), familyList);
    }

}


                        
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