LinkedHashMap$Entry 不能转换为 java.util.LinkedHashMap
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/21215681/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
LinkedHashMap$Entry cannot be cast to java.util.LinkedHashMap
提问by quartaela
I'm wrapped LinkedHashMap<String, LinkedHashMap<Date, Double>>into a List with;
我被包裹LinkedHashMap<String, LinkedHashMap<Date, Double>>在一个列表中；
List<LinkedHashMap<String, LinkedHashMap<Date, Double>>> list = new ArrayList(mainCodesMap.entrySet());
which mainCodeMapis type of Map<String, Map<Date, Double>>
这mainCodeMap是类型Map<String, Map<Date, Double>>
the thing is there is no problem with list,however, when I try to get elements of list by index in a for loop like;
问题是列表没有问题，但是，当我尝试在 for 循环中按索引获取列表元素时；
for (int i = 0; i < correMatrix.length; i++) {
LinkedHashMap<String, LinkedHashMap<Date, Double>> entryRow = list.get(i);
LinkedHashMap<Date, Double> entryRowData = (LinkedHashMap<Date, Double>) entryRow.values();
..
..
}
jvm throws ClassCastExceptionwhich says;
jvm throwsClassCastException说；
java.lang.ClassCastException: java.util.LinkedHashMap$Entry cannot be cast to java.util.LinkedHashMap
采纳答案by user253751
List<LinkedHashMap<String, LinkedHashMap<Date, Double>>> list = new ArrayList(mainCodesMap.entrySet());
mainCodesMap.entrySetreturns a Set<Map.Entry<...>>(not literally ...). You then create an ArrayListcontaining these Map.Entrys. Because you are using the raw type ArrayList(instead of ArrayList<something>) the compiler can't catch this problem.
mainCodesMap.entrySet返回一个Set<Map.Entry<...>>（不是字面意思...）。然后创建一个ArrayList包含这些Map.Entrys 的对象。因为您使用的是原始类型ArrayList（而不是ArrayList<something>），所以编译器无法捕捉到这个问题。
It looks like you actually meant this:
看起来你的意思是这样的：
List<LinkedHashMap<String, LinkedHashMap<Date, Double>>> list = new ArrayList<>();
list.add(mainCodesMap)
Note: ArrayList<>means the compiler will automatically fill in the <>. It doesn't work in all contexts.
注意：ArrayList<>表示编译器会自动填写<>。它不适用于所有情况。
