Java 泛型和有界类型

Question

我有一个 ConcurrentMap 的包装类，如下所示:

public MapWrapper<K, V> implements ConcurrentMap<K, V> {

    private final ConcurrentMap<K, V> wrappedMap;

    ...
    @Override
    public void putAll(Map<? extends K, ? extends V> map) {
        wrappedMap.putAll(map);  // <--- Gives compilation error
    }
    ...
}

标记的行会触发以下编译错误:

method putAll in interface java.util.Map<K,V> cannot be applied to given types;
required: java.util.Map<? extends capture#5 of ? extends K,? extends capture#6 of ?
    extends V>
found: java.util.Map<capture#7 of ? extends K,capture#8 of ? extends V>
reason: actual argument java.util.Map<capture#7 of ? extends K,capture#8 of ? extends V> 
    cannot be converted to java.util.Map<? extends capture#5 of ? extends K,? extends 
    capture#6 of ? extends V> by method invocation conversion

我怀疑无限通配符是罪魁祸首，但我无法更改方法签名，因为它是从 ConcurrentMap 接口(interface)继承的。有任何想法吗？

Answer 1

你见过吗:

What is the difference between bounded wildcard and type parameters?