如何从具有不同值类型的Map中获取值?(Java) [英] How to get values from a Map with different value types? (Java)

问题描述

我有一个实用函数，该函数返回 Map< String，Object> ，但是Map始终具有以下结构:

I have a utility function that returns Map<String, Object>, but that Map always has this structure:

{ "a": <something of type1>, "b": <something of type2> }

在外部函数中，我将其称为实用程序函数，我想获取与键 a 相关的值.我正在尝试执行以下操作:

In outer function, where I call this utility function, I want to get the value associated with key a. I'm trying to do something such as:

Map<String, Object> data = findData(input); // findData is the utility function
Type1 type1obj = data.get("a"); // error here

但随后出现不兼容类型"错误:

But then I get the Incompatible Types error:

Required: com.blah.blah.Type1
Found: java.lang.Object

我应该如何获取与键 a 相关的值?仅供参考:我是Java的新手.

How am I supposed to grab the value associated with key a? FYI: I'm VERY new to Java.

推荐答案

您需要将从Map检索到的对象转换为所需的类型:

You need to cast the Object retrieved from Map to the type you required:

Type1 type1obj = (Type1) data.get("a");

但是在上面的代码中，您必须确保与键"a"关联的值的类型为Type1，否则将在运行时引发 ClassCastException .

But with the code above you have to make sure the type of value associated with key "a" is Type1, otherwise a ClassCastException will thrown at runtime.

如果您不能保证所检索对象的类型，可以按照以下方式进行检查:

If you cannot guarantee the type of the Object retrieved, you can check it like:

Object obj = data.get("a");
Type1 type1obj;
if(obj instanceof Type1) {
    type1obj = (Type1) obj;
} else {
    //to print error log or do some workaround
}

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