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 *
067 * @since 3.0
068 */
069@StatelessCheck
070public class SimplifyBooleanExpressionCheck
071        extends AbstractCheck {
072
073    /**
074     * A key is pointing to the warning message text in "messages.properties"
075     * file.
076     */
077    public static final String MSG_KEY = "simplify.expression";
078
079    @Override
080    public int[] getDefaultTokens() {
081        return getRequiredTokens();
082    }
083
084    @Override
085    public int[] getAcceptableTokens() {
086        return getRequiredTokens();
087    }
088
089    @Override
090    public int[] getRequiredTokens() {
091        return new int[] {TokenTypes.LITERAL_TRUE, TokenTypes.LITERAL_FALSE};
092    }
093
094    @Override
095    public void visitToken(DetailAST ast) {
096        final DetailAST parent = ast.getParent();
097        switch (parent.getType()) {
098            case TokenTypes.NOT_EQUAL:
099            case TokenTypes.EQUAL:
100            case TokenTypes.LNOT:
101            case TokenTypes.LOR:
102            case TokenTypes.LAND:
103                log(parent, MSG_KEY);
104                break;
105            default:
106                break;
107        }
108    }
109
110}