What does a tilde in angle brackets mean when creating a Java generic class?

Question

I was reading through some JMockit examples and found this code:

final List<OrderItem> actualItems = new ArrayList<~>();

What does the tilde in the generic identifier mean? I know it's the unary bitwise NOT operator, but I don't see an operand here.

Also, I tried compiling it and got an error. Am I just missing something?

roottraveller · Accepted Answer · 2018-04-08 06:16:48Z

178

It is just a shorthand for "same as in declaration".

Some IDEs, e.g. IntelliJ use this too.

The files on disk do not have this notation, which is only a compaction in the IDE GUI.

edited Apr 8, 2018 at 6:16

roottraveller

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answered Feb 3, 2011 at 15:12

openCage

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5 Comments

Michael K Over a year ago

It was an Intellij screenshot.

Andreas Dolk Over a year ago

Just for personal clarification - IntelliJ produces Java source files with this notation, iaw, source files with illegal Java content??? Or is this just the view of the source and the saved file is correct?

openCage Over a year ago

@Andreas_D: It is just a view. The files on disk are ok.

yshavit Over a year ago

And actually, the tilde is grayed (to indicate that it's different), and if you click on it, it'll expand to the full definition.

Ocie Mitchell Over a year ago

This can be disabled in the intelij settings for editor/general/Code Folding.

Andreas Dolk · Accepted Answer · 2011-02-03 15:51:39Z

If there wasn't a tilde, I'd say, the code was already Java 7. Java 7 allows the diamond operator so this is/will be legal Java code:

Map<String, List<String>> map = new HashMap<>();

(but - no tilde with this syntax)

Ascendant · Accepted Answer · 2015-02-19 22:50:14Z

In IntelliJ IDEA, the ~ here:

Set<String> associations = new LinkedHashSet<~>();

means String, which is the same as in the declaration on the left side.

Andrew White · Accepted Answer · 2011-02-03 15:12:06Z

2

I think that is shorthand to mean whatever the type is, in this case OrderItem.

answered Feb 3, 2011 at 15:12

Andrew White

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