1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2026 the original author or authors.
4 //
5 // This library is free software; you can redistribute it and/or
6 // modify it under the terms of the GNU Lesser General Public
7 // License as published by the Free Software Foundation; either
8 // version 2.1 of the License, or (at your option) any later version.
9 //
10 // This library is distributed in the hope that it will be useful,
11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 // Lesser General Public License for more details.
14 //
15 // You should have received a copy of the GNU Lesser General Public
16 // License along with this library; if not, write to the Free Software
17 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18 ///////////////////////////////////////////////////////////////////////////////////////////////
19
20 package com.puppycrawl.tools.checkstyle.checks.coding;
21
22 import com.puppycrawl.tools.checkstyle.StatelessCheck;
23 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
24 import com.puppycrawl.tools.checkstyle.api.DetailAST;
25 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
26 import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
27
28 /**
29 * <div>
30 * Checks for over-complicated boolean expressions. Currently, it finds code like
31 * {@code if (b == true)}, {@code b || true}, {@code !false},
32 * {@code boolean a = q > 12 ? true : false},
33 * etc.
34 * </div>
35 *
36 * <p>
37 * Rationale: Complex boolean logic makes code hard to understand and maintain.
38 * </p>
39 *
40 * @since 3.0
41 */
42 @StatelessCheck
43 public class SimplifyBooleanExpressionCheck
44 extends AbstractCheck {
45
46 /**
47 * A key is pointing to the warning message text in "messages.properties"
48 * file.
49 */
50 public static final String MSG_KEY = "simplify.expression";
51
52 /**
53 * Creates a new {@code SimplifyBooleanExpressionCheck} instance.
54 */
55 public SimplifyBooleanExpressionCheck() {
56 // no code by default
57 }
58
59 @Override
60 public int[] getDefaultTokens() {
61 return getRequiredTokens();
62 }
63
64 @Override
65 public int[] getAcceptableTokens() {
66 return getRequiredTokens();
67 }
68
69 @Override
70 public int[] getRequiredTokens() {
71 return new int[] {TokenTypes.LITERAL_TRUE, TokenTypes.LITERAL_FALSE};
72 }
73
74 @Override
75 public void visitToken(DetailAST ast) {
76 final DetailAST parent = ast.getParent();
77 switch (parent.getType()) {
78 case TokenTypes.NOT_EQUAL,
79 TokenTypes.EQUAL,
80 TokenTypes.LNOT,
81 TokenTypes.LOR,
82 TokenTypes.LAND -> log(parent, MSG_KEY);
83
84 case TokenTypes.QUESTION -> {
85 final DetailAST firstChild = skipParentheses(parent.getFirstChild());
86 final DetailAST nextSibling = skipParentheses(ast.getNextSibling());
87 if (TokenUtil.isBooleanLiteralType(firstChild.getType())
88 || nextSibling != null
89 && TokenUtil.isBooleanLiteralType(
90 skipParentheses(nextSibling.getNextSibling()).getType())) {
91 log(parent, MSG_KEY);
92 }
93 }
94
95 default -> {
96 // do nothing
97 }
98 }
99 }
100
101 /**
102 * Iterates sibling nodes, skipping parentheses.
103 *
104 * @param node The starting node.
105 * @return The first sibling not of type {@code TokenTypes.LPAREN} or
106 * {@code TokenTypes.RPAREN}, or {@code null} if no such node exists.
107 */
108 private static DetailAST skipParentheses(DetailAST node) {
109 DetailAST result = node;
110 while (TokenUtil.isOfType(result, TokenTypes.LPAREN, TokenTypes.RPAREN)) {
111 result = result.getNextSibling();
112 }
113 return result;
114 }
115
116 }