将通用Class参数限制为实现Map的类 [英] Restrict a generic Class parameter to classes that implement Map

问题描述

我正在尝试编写一个Map构建器.其中一个构造函数将允许客户端指定他们希望构建的Map的类型

I'm trying to write a Map builder. One of the constructors will allow the client to specify the type of Map they wish to build

public class MapBuilder<K, V> {

    private Map<K, V> map;

    /**
     * Create a Map builder
     * @param mapType the type of Map to build. This type must support a default constructor
     * @throws Exception
     */
    public MapBuilder(Class<? extends Map<K, V>> mapType) throws Exception {
        map = mapType.newInstance();
    }

    // remaining implementation omitted
}

目的是应该可以通过以下方式构造构建器的实例:

The intent is that it should be possible to construct instances of the builder with:

MapBuilder<Integer, String> builder = new MapBuilder<Integer, String>(LinkedHashMap.class);

或

MapBuilder<Integer, String> builder = new MapBuilder<Integer, String>(HashMap.class);

似乎构造函数参数的类型签名当前不支持此功能，因为上面的行会导致无法解析构造函数"编译错误.

It seems that the type signature of the constructor argument doesn't currently support this, because the line above causes a "Cannot resolve constructor" compilation error.

如何更改构造函数，使其接受仅实现Map的类?

How can I change my constructor so that it accepts classes that implement Map only?

推荐答案

使用Supplier代替Class:

public MapBuilder(Supplier<? extends Map<K, V>> supplier) {
    map = supplier.get();
}

然后可以这样称呼它:

MapBuilder<Integer, Integer> builder = new MapBuilder<>(LinkedHashMap::new);

这也更安全，因为Class<Map>可能没有默认构造函数，这会引发错误(代码响应性不强)

This is also safer, because a Class<Map> could have no default constructor, which would throw an error (which is not very responsive code)

这篇关于将通用Class参数限制为实现Map的类的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！