001////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code for adherence to a set of rules.
003// Copyright (C) 2001-2020 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.checks.coding;
021
022import com.puppycrawl.tools.checkstyle.StatelessCheck;
023import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
024import com.puppycrawl.tools.checkstyle.api.DetailAST;
025import com.puppycrawl.tools.checkstyle.api.TokenTypes;
026
027/**
028 * <p>
029 * Checks for over-complicated boolean expressions. Currently finds code like
030 * {@code if (b == true)}, {@code b || true}, {@code !false},
031 * etc.
032 * </p>
033 * <p>
034 * Rationale: Complex boolean logic makes code hard to understand and maintain.
035 * </p>
036 * <p>
037 * To configure the check:
038 * </p>
039 * <pre>
040 * &lt;module name=&quot;SimplifyBooleanExpression&quot;/&gt;
041 * </pre>
042 * <p>Example:</p>
043 * <pre>
044 * public class Test {
045 *
046 *   public void bar() {
047 *
048 *     boolean a, b;
049 *     Foo c, d, e;
050 *
051 *     if (!false) {}; // violation, can be simplified to true
052 *
053 *     if (a == true) {}; // violation, can be simplified to a
054 *     if (a == b) {}; // OK
055 *     if (a == false) {}; // violation, can be simplified to !a
056 *     if (!(a != true)) {}; // violation, can be simplified to a
057 *
058 *     e = (a || b) ? c : d; // OK
059 *     e = (a || false) ? c : d; // violation, can be simplified to a
060 *     e = (a &amp;&amp; b) ? c : d; // OK
061 *
062 *  }
063 *
064 * }
065 * </pre>
066 * <p>
067 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
068 * </p>
069 * <p>
070 * Violation Message Keys:
071 * </p>
072 * <ul>
073 * <li>
074 * {@code simplify.expression}
075 * </li>
076 * </ul>
077 *
078 * @since 3.0
079 */
080@StatelessCheck
081public class SimplifyBooleanExpressionCheck
082        extends AbstractCheck {
083
084    /**
085     * A key is pointing to the warning message text in "messages.properties"
086     * file.
087     */
088    public static final String MSG_KEY = "simplify.expression";
089
090    @Override
091    public int[] getDefaultTokens() {
092        return getRequiredTokens();
093    }
094
095    @Override
096    public int[] getAcceptableTokens() {
097        return getRequiredTokens();
098    }
099
100    @Override
101    public int[] getRequiredTokens() {
102        return new int[] {TokenTypes.LITERAL_TRUE, TokenTypes.LITERAL_FALSE};
103    }
104
105    @Override
106    public void visitToken(DetailAST ast) {
107        final DetailAST parent = ast.getParent();
108        switch (parent.getType()) {
109            case TokenTypes.NOT_EQUAL:
110            case TokenTypes.EQUAL:
111            case TokenTypes.LNOT:
112            case TokenTypes.LOR:
113            case TokenTypes.LAND:
114                log(parent, MSG_KEY);
115                break;
116            default:
117                break;
118        }
119    }
120
121}