Java Checkstyle Rule To Restrict Method Empty Lines - checkstyle

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;
doStuff(a);
-
-
doMoreStuff(a);
-
}
In the example above, I have denoted empty lines with - characters.
I'd like to be able to to prevent the leading line, trailing line and more than one line in the method body.

Answer 1

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 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="(?<=\{\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="(?<!\{\s{0,99}$)^$(?=^\s{0,99}\})" />
<property name="fileExtensions" value="groovy,java" />
</module>
"^$" signifies the blank line.

Answer 3

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.

Answer 4

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 5

This is my suggestion for checking for blank lines at the beginning of method
<module name="RegexpMultiline">
<property name="id" value="RegexpMultilineEmptyRowBeforeStartOfMethod"/>
<property name="message" value="Blank line at start of method or block should be removed"/>
<property name="format" value="\)(\s)*\{\r?\n(\s)*\n"/>
<property name="fileExtensions" value="java"/>
</module>