类似字典的数据结构。这是一个好习惯吗？ [英] Dictionary-like data structure. Is this a good practice?

问题描述

我需要一个数据结构来存储不同类型的对象。 String ，布尔值和其他类。

使用 Map< ; String，Object> 其中使用你获得相应对象的键，假设你知道如何投掷它一个很好的做法？

有更好的解决方案吗？

I need a data structure to store different type of objects.E.g. String, Boolean and other classes.
Is using a Map<String, Object> where using the key you get the according object which assumes that you know how to cast it a good practice?
Is there a better solution?

推荐答案

这是一个完美的用例，一段时间以前写过的 PropretyHolder 您可以在我的博客上阅读更多信息。我开发了它与不变性的心灵，随意适应你的需要。

That's a perfect use case for a PropretyHolder I wrote a while ago. You can read in length about it on my blog. I developed it with immutability in mind, feel free to adapt it to your needs.

一般来说，我想说如果你想从Java中的类型安全性中获利知道你的钥匙我的意思是 - 几乎不可能开发类型的安全解决方案，其中钥匙来自外部来源。

In general I'd say if you want to profit from type safety in Java you need to know your keys. What I mean by that - it will be hardly possible to develop type safe solution where keys come from external source.

这里是知道其价值类型的特殊键（不完整，请下载源完整版本）：

Here's a special key that knows type of its value (it's not complete please download the source for complete version):

public class PropertyKey<T> {
    private final Class<T> clazz;
    private final String name;

    public PropertyKey(Class<T> valueType, String name) {
        this.clazz = valueType;
        this.name = name;
    }

    public boolean checkType(Object value) {
        if (null == value) {
            return true;
        }
        return this.clazz.isAssignableFrom(value.getClass());
    }

    ... rest of the class

}

然后你开发一个利用它的数据结构：

Then you develop a data structure that utilizes it:

public class PropertyHolder {

    private final ImmutableMap<PropertyKey<?>, ?> storage;

    /**
     * Returns value for the key of the type extending-the-one-declared-in-the {@link PropertyKey}.
     * 
     * @param key {@link PropertyKey} instance.
     * @return Value of the type declared in the key.
     */
    @SuppressWarnings("unchecked")
    public <T extends Serializable> T get(PropertyKey<T> key) {
        return (T) storage.get(key);
    }

    /**
     * Adds key/value pair to the state and returns new 
     * {@link PropertyHolder} with this state.
     * 
     * @param key {@link PropertyKey} instance.
     * @param value Value of type specified in {@link PropertyKey}.
     * @return New {@link PropertyHolder} with updated state.
     */
    public <T> PropertyHolder put(PropertyKey<T> key, T value) {
        Preconditions.checkNotNull(key, "PropertyKey cannot be null");
        Preconditions.checkNotNull(value, "Value for key %s is null", 
                key);
        Preconditions.checkArgument(key.checkType(value), 
                "Property \"%s\" was given " 
                + "value of a wrong type \"%s\"", key, value);
        // Creates ImmutableMap.Builder with new key/value pair.
        return new PropertyHolder(filterOutKey(key)
                .put(key, value).build());
    }

    /**
     * Returns {@link Builder} with all the elements from the state except for the given ket.
     * 
     * @param key The key to remove.
     * @return {@link Builder} for further processing.
     */
    private <T> Builder<PropertyKey<? extends Serializable>, Serializable> filterOutKey(PropertyKey<T> key) {
        Builder<PropertyKey<? extends Serializable>, Serializable> builder = ImmutableMap
                .<PropertyKey<? extends Serializable>, Serializable> builder();
        for (Entry<PropertyKey<? extends Serializable>, Serializable> entry : this.storage.entrySet()) {
            if (!entry.getKey().equals(key)) {
                builder.put(entry);
            }
        }
        return builder;
    }

    ... rest of the class

}

我在这里省略了很多不必要的细节，如果有什么不清楚，请告诉我。

I omit here a lot of unnecessary details please let me know if something is not clear.

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