How to fix incompatible types: java.lang.Object cannot be converted to java.util.List

Question

I have a hashmap defined like this that I cant change

private Map<String, Object> attributes;

The object is a list of Strings (sometimes size == 1, other times > 1).

I have an instance of the attributes map later on in the execution. I am wanna get the Object as List.

This:

List<String> outputs = attributes.get("keys");

throws this error.

incompatible types: java.lang.Object cannot be converted to java.util.List<java.lang.String>

How can I fix it?

`List outputs = (List) attributes.get("keys");` – Unmitigated Apr 21 '21 at 20:33 — Unmitigated, Apr 21 '21 at 20:33

score 3 · Accepted Answer · edited Apr 22 '21 at 18:30

3

Use an explicit cast:

List<String> outputs = (List<String>) attributes.get("keys");

Note that this is an unchecked cast and may throw ClassCastException at runtime.

edited Apr 22 '21 at 18:30

answered Apr 21 '21 at 20:34

Unmitigated

You should explain that this is an unchecked cast, and what that means for type safety. – Andy Turner Apr 21 '21 at 20:35

1 Answers1