HashMap get(Object)总是返回String而不是其他Object

问题描述：

遇到一个困扰我的问题.我有一个HashMap声明为使用字符串作为键，并使用我自己的KWIKattribute作为值.

Having an issue that is just stumping me. I have a HashMap declared to use a String as the Key and my own KWIKattribute as the Value.

private HashMap<String, KWIKattribute> attributes = new HashMap<String, KWIKattribute>();

我将对象放入其中，其中sgml_xml_tag是字符串，而kattr是KWIKattribute的实例.

I put objects into it, where sgml_xml_tag is a String and kattr is an instance of KWIKattribute.

attributes.put(sgml_xml_tag, kattr);

当我尝试将其值作为KWIKattribute收回时

When I try to get the value back out as a KWIKattribute

for (Map.Entry<String, KWIKattribute> e : attributes.entrySet()) {
        String key = e.getKey();
        KWIKattribute kattr = (KWIKattribute) attributes.get(e.getKey());
}

引发异常

javax.faces.el.EvaluationException: java.lang.ClassCastException: java.lang.String cannot be cast to com.northgrum.adt.kwik.model.KWIKattribute

我知道这对我而言可能是一个简单的愚蠢错误，但我看不到它是什么.有什么建议吗?

I know this is probably a simple stupid error on my part somewhere, but I'm not seeing what it is. Any suggestions?

答

用于迭代Map条目集的 Map.Entry 类具有 getValue()-方法，它将值返回到当前键.

The Map.Entry-class, which you use to iterate over the entry-set of your Map has a getValue()-method, which returns the value to the current key.

否则，如果您仅对Map中的值感兴趣，则还可以遍历

Otherwise, if you're only interested in the values from the Map, you can also iterate over the values-collection:

for (KWIKattribute attr : attributes.values()){
  // Do your work with attr
}

HashMap get(Object)总是返回String而不是其他Object

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