build: Add OperatorWrap rule to checkstyle

[Oliver-Loeffler]

As learned with issue-73, operators are supposed to be wrapped into spaces.
Nicely Checkstyle has a rule for that.

Expected Behavior

Unwrapped operators such as in content=textArea.getText(); should be detected by Checkstyle.
Checkstyle should issue a warning for such cases. Ideally the source looks like: content = textArea.getText();.

Current Behavior

Checkstyle does not detect those, as it does not check for this pattern.

Context

Inconvenience / extra effort in Pull Request reviews. Would be good if we could avoid this by using Checkstyle.

I'll open a PR with a modified checkstyle.xml.
If there other rules we should implement, we can do this in the related PR.

[Oliver-Loeffler]

Actually I was wrong with this one. Just played around with Checkstyle and found that OperatorWrap only ensures that we get the following pattern when line wraps are needed:

Checkstyle will complain this one:

        int d = c +
                10;

It will permit:

        int d = c
                + 10;

Nevertheless, this rule is okay to have. What I actually wanted (I am sorry, did not check carefully enough) is the following:

        <module name="WhitespaceAfter"/>
        <module name="WhitespaceAround"/>

This setup ensures that we actually get the whitespaces around lambdas, around operators +, ||, etc.
Interestingly this also ensures that we have actually no whitespace before comma but a following whitespace after the comma.
I'll test my PRs using those settings and rework them accordingly.

If you agree @abhinayagarwal, I'll issue an updated PR referring this issue.

[Oliver-Loeffler]

One more question @abhinayagarwal , should we apply Checkstyle also to the test sources?

[abhinayagarwal]

My preference would be for all java sources to have these checkstyles.

[Oliver-Loeffler]

I will see to geht this working for the tests as well.