Java Checkstyle Rule To Restrict Method Empty Lines

Question

Is there a way to setup checkstyle to prevent leading, multiple or trailing empty lines in method bodies:

e.g.

private void a() {
-
int a = 1;
doStu         


        

Answer 1

Can use it:

<module name="Regexp">
    <property name="message" value="Blank line at start of block is not allowed"/>
    <property name="format" value="\{\s*$^\s*$"/>
    <property name="ignoreComments" value="true"/>
    <property name="illegalPattern" value="true"/>
</module>
<module name="Regexp">
    <property name="message" value="Blank line at end of block is not allowed"/>
    <property name="format" value="^\s*$^\s*\}"/>
    <property name="ignoreComments" value="true"/>
    <property name="illegalPattern" value="true"/>
</module>

Answer 2

To enforce no blank lines at the beginning and end of any block, you can use multi-line regular expression checks:

<module name="RegexpMultiline">
    <property name="message" value="Blank line at start of block should be removed" />
    <property name="format" value="(?&lt;=\{\s{0,99}$)^$" />
    <property name="fileExtensions" value="groovy,java" />
</module>
<module name="RegexpMultiline">
    <property name="message" value="Blank line at end of block should be removed" />
    <property name="format" value="(?&lt;!\{\s{0,99}$)^$(?=^\s{0,99}\})" />
    <property name="fileExtensions" value="groovy,java" />
</module>

"^$" signifies the blank line.

Answer 3

To prevent leading empty lines in method bodies, you can use:

<module name="RegexpMultiline">
    <property name="message" value="Blank line at start of method should be removed"/>
    <property name="format" value="\(.*\)\s*\{\s*\n\s*\n"/>
</module>

We can find method by parentheses.

Answer 4

To prevent multiple empty lines you can use the EmptyLineSeparator check. Its primary purpose is to ensure that there is an empty line between members in a file, but it also has a allowMultipleEmptyLines property which you can set to "false" to disallow them.

There is however currently a bug with the check that means it doesn't correctly detect multiple empty lines between methods where there is a comment (including JavaDoc) between the methods. I am working on a fix for this at the moment.

As for checking for new lines at the beginning or end of a block, I think the RegexpMultiline check would be the only option as mentioned in Pankaj's answer.