HashMap(key: String, value: ArrayList) returns an Object instead of ArrayList?

Question

I\'m storing data in a HashMap with (key: String, value: ArrayList). The part I\'m having trouble with declares a new ArrayList \"current,\" searches the HashMap for the String

Answer 1

How is the HashMap declaration expressed in that scope? It should be:

HashMap dictMap

If not, it is assumed to be Objects.

For instance, if your code is:

HashMap dictMap = new HashMap();
...
ArrayList current = dictMap.get(dictCode);

that will not work. Instead you want:

HashMap dictMap = new HashMap();
...
ArrayList current = dictMap.get(dictCode);

The way generics work is that the type information is available to the compiler, but is not available at runtime. This is called type erasure. The implementation of HashMap (or any other generics implementation) is dealing with Object. The type information is there for type safety checks during compile time. See the Generics documentation.

Also note that ArrayList is also implemented as a generic class, and thus you might want to specify a type there as well. Assuming your ArrayList contains your class MyClass, the line above might be:

HashMap> dictMap