[SOLVED] Why not Set<String> set = new HashSet() instead of Set<String> set = new HashSet<String>()?

Why not Set<String> set = new HashSet() instead of Set<String> set = new HashSet<String>()?

Everywhere I look, I see the typing of Collections done like this:

Set<String> set = new HashSet<String>();

However, I define my Collections like this

Set<String> set = new HashSet();

and I still get the type checking (and my way is just cleaner to look at).

Maybe this has something to do when creating generic collections? But, let's say I just want nothing more than a HashSet of Strings, then is not

Set<String> set = new HashSet();

enough?

Solution

You are using a generic class when creating a new collection.

The generic class must get the generic type it encapsulates, otherwise it is considered a Raw Type.

The proper declaration of the collection value, should therefore be:

Set<String> mySet = new HashSet<>();

Your JVM will be able to infer the generic type being used in your HashSet thanks to the declaration on Set<String>

Most IDEs (Eclipse and ItelliJ, for example) will have their linters configured to provide a warning when using a Raw Type class. This warning can be suppressed, but that is considered a bad practice.

References:

Bonus:

What is "Linting"?