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.
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.
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>
"^$" signifies the blank line.
To prevent multiple empty lines you can use the EmptyLineSeparator check. Its primary purpose is to ensure that there is an empty line between members in a file, but it also has a allowMultipleEmptyLines property which you can set to "false" to disallow them.
There is however currently a bug with the check that means it doesn't correctly detect multiple empty lines between methods where there is a comment (including JavaDoc) between the methods. I am working on a fix for this at the moment.
As for checking for new lines at the beginning or end of a block, I think the RegexpMultiline check would be the only option as mentioned in Pankaj's answer.
Can use it:
<module name="Regexp">
<property name="message" value="Blank line at start of block is not allowed"/>
<property name="format" value="\{\s*$^\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>
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>
check-tfij-style contains a checkstyle check to restrict any empty lines in methods or constructors. Just add maven/gradle dependency to checkstyle plugin:
plugins {
java
checkstyle
}
dependencies {
checkstyle("pl.tfij:check-tfij-style:1.5.1")
}
Then add the check to your checkstyle config:
<module name="MethodEmptyLines"/>
The answers here discuss preventing leading and trailing lines at the beginning and ends of method blocks, but don't answer the part of the question that asks how to prevent multiple repeating empty lines (non-leading or trailing) within a method block.
To prevent that we can use:
<module name="EmptyLineSeparator">
<property name="allowMultipleEmptyLinesInsideClassMembers" value="false"/>
</module>
https://checkstyle.sourceforge.io/version/8.40/config_whitespace.html
