LambdaBodyLengthCheck.java
///////////////////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
// Copyright (C) 2001-2022 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
///////////////////////////////////////////////////////////////////////////////////////////////
package com.puppycrawl.tools.checkstyle.checks.sizes;
import com.puppycrawl.tools.checkstyle.StatelessCheck;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
/**
* <p>
* Checks lambda body length.
* </p>
* <p>
* Rationale: Similar to anonymous inner classes, if lambda body becomes very long
* it is hard to understand and to see the flow of the method
* where the lambda is defined. Therefore, long lambda body
* should usually be extracted to method.
* </p>
* <ul>
* <li>
* Property {@code max} - Specify the maximum number of lines allowed.
* Type is {@code int}.
* Default value is {@code 10}.
* </li>
* </ul>
* <p>
* To configure the check to accept lambda bodies with up to 10 lines:
* </p>
* <pre>
* <module name="LambdaBodyLength"/>
* </pre>
* <p>
* Example:
* </p>
* <pre>
* class Test {
* Runnable r = () -> { // violation, 11 lines
* System.out.println(2); // line 2 of lambda
* System.out.println(3);
* System.out.println(4);
* System.out.println(5);
* System.out.println(6);
* System.out.println(7);
* System.out.println(8);
* System.out.println(9);
* System.out.println(10);
* }; // line 11
*
* Runnable r2 = () -> // violation, 11 lines
* "someString".concat("1") // line 1 of lambda
* .concat("2")
* .concat("3")
* .concat("4")
* .concat("5")
* .concat("6")
* .concat("7")
* .concat("8")
* .concat("9")
* .concat("10")
* .concat("11"); // line 11
*
* Runnable r3 = () -> { // ok, 10 lines
* System.out.println(2); // line 2 of lambda
* System.out.println(3);
* System.out.println(4);
* System.out.println(5);
* System.out.println(6);
* System.out.println(7);
* System.out.println(8);
* System.out.println(9);
* }; // line 10
* }
* </pre>
* <p>
* To configure the check to accept lambda bodies with max 5 lines:
* </p>
* <pre>
* <module name="LambdaBodyLength">
* <property name="max" value="5"/>
* </module>
* </pre>
* <p>
* Example:
* </p>
* <pre>
* class Test {
* Runnable r = () -> { // violation, 6 lines
* System.out.println(2); // line 2 of lambda
* System.out.println(3);
* System.out.println(4);
* System.out.println(5);
* };
*
* Runnable r2 = () -> // violation, 6 lines
* "someString".concat("1")
* .concat("2")
* .concat("3")
* .concat("4")
* .concat("5")
* .concat("6");
*
* Runnable r3 = () -> { // ok, 5 lines
* System.out.println(2);
* System.out.println(3);
* System.out.println(4);
* };
* }
* </pre>
* <p>
* Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
* </p>
* <p>
* Violation Message Keys:
* </p>
* <ul>
* <li>
* {@code maxLen.lambdaBody}
* </li>
* </ul>
*
* @since 8.37
*/
@StatelessCheck
public class LambdaBodyLengthCheck extends AbstractCheck {
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_KEY = "maxLen.lambdaBody";
/** Default maximum number of lines. */
private static final int DEFAULT_MAX = 10;
/** Specify the maximum number of lines allowed. */
private int max = DEFAULT_MAX;
/**
* Setter to specify the maximum number of lines allowed.
*
* @param length the maximum length of lambda body.
*/
public void setMax(int length) {
max = length;
}
@Override
public int[] getDefaultTokens() {
return getRequiredTokens();
}
@Override
public int[] getAcceptableTokens() {
return getRequiredTokens();
}
@Override
public int[] getRequiredTokens() {
return new int[] {TokenTypes.LAMBDA};
}
@Override
public void visitToken(DetailAST ast) {
if (ast.getParent().getType() != TokenTypes.SWITCH_RULE) {
final int length = getLength(ast);
if (length > max) {
log(ast, MSG_KEY, length, max);
}
}
}
/**
* Get length of lambda body.
*
* @param ast lambda body node.
* @return length of lambda body.
*/
private static int getLength(DetailAST ast) {
final DetailAST lambdaBody = ast.getLastChild();
final int length;
if (lambdaBody.getType() == TokenTypes.SLIST) {
length = lambdaBody.getLastChild().getLineNo() - lambdaBody.getLineNo();
}
else {
length = getLastNodeLineNumber(lambdaBody) - getFirstNodeLineNumber(lambdaBody);
}
return length + 1;
}
/**
* Get last child node in the tree line number.
*
* @param lambdaBody lambda body node.
* @return last child node in the tree line number.
*/
private static int getLastNodeLineNumber(DetailAST lambdaBody) {
DetailAST node = lambdaBody;
int result;
do {
result = node.getLineNo();
node = node.getLastChild();
} while (node != null);
return result;
}
/**
* Get first child node in the tree line number.
*
* @param lambdaBody lambda body node.
* @return first child node in the tree line number.
*/
private static int getFirstNodeLineNumber(DetailAST lambdaBody) {
DetailAST node = lambdaBody;
int result;
do {
result = node.getLineNo();
node = node.getFirstChild();
} while (node != null);
return result;
}
}