code format: using the same code style

[liukun4515]

We use the different code style, which leads to a lot of diffs in prs. Unifying the code style is better. We can reference to google-java-format and checkstyle

[MyXOF]

We used different environments(Windows, OSX, Linux) during previous development. Now since everyone has an OSX environment, it will be convenient to unify our code style.

[liukun4515]

We can add checkstyle plugin in pom.xml to check code style

[jt2594838]

I think a simple Reformat the code command before any commit will just do the trick. For non-IDE-users, figure out your own way.

[liukun4515]

Using the google-java-format plugin can help us to format code when compiling the code. You can use mvn compile to format your code, before submitting it. We can add checkstyle plugin to validate the code style and add checker in CI. @jt2594838

[jixuan1989]

checkstyle +1