Source code

001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2025 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.metrics;
021
022import java.math.BigInteger;
023import java.util.ArrayDeque;
024import java.util.Deque;
025
026import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
027import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
028import com.puppycrawl.tools.checkstyle.api.DetailAST;
029import com.puppycrawl.tools.checkstyle.api.TokenTypes;
030import com.puppycrawl.tools.checkstyle.utils.ScopeUtil;
031
032/**
033 * <div>
034 * Checks cyclomatic complexity against a specified limit. It is a measure of
035 * the minimum number of possible paths through the source and therefore the
036 * number of required tests, it is not about quality of code! It is only
037 * applied to methods, c-tors,
038 * <a href="https://docs.oracle.com/javase/tutorial/java/javaOO/initial.html">
039 * static initializers and instance initializers</a>.
040 * </div>
041 *
042 * <p>
043 * The complexity is equal to the number of decision points {@code + 1}.
044 * Decision points:
045 * </p>
046 * <ul>
047 * <li>
048 * {@code if}, {@code while}, {@code do}, {@code for},
049 * {@code ?:}, {@code catch}, {@code switch}, {@code case} statements.
050 * </li>
051 * <li>
052 *  Operators {@code &amp;&amp;} and {@code ||} in the body of target.
053 * </li>
054 * <li>
055 *  {@code when} expression in case labels, also known as guards.
056 * </li>
057 * </ul>
058 *
059 * <p>
060 * By pure theory level 1-4 is considered easy to test, 5-7 OK, 8-10 consider
061 * re-factoring to ease testing, and 11+ re-factor now as testing will be painful.
062 * </p>
063 *
064 * <p>
065 * When it comes to code quality measurement by this metric level 10 is very
066 * good level as a ultimate target (that is hard to archive). Do not be ashamed
067 * to have complexity level 15 or even higher, but keep it below 20 to catch
068 * really bad-designed code automatically.
069 * </p>
070 *
071 * <p>
072 * Please use Suppression to avoid violations on cases that could not be split
073 * in few methods without damaging readability of code or encapsulation.
074 * </p>
075 *
076 * @since 3.2
077 */
078@FileStatefulCheck
079public class CyclomaticComplexityCheck
080    extends AbstractCheck {
081
082    /**
083     * A key is pointing to the warning message text in "messages.properties"
084     * file.
085     */
086    public static final String MSG_KEY = "cyclomaticComplexity";
087
088    /** The initial current value. */
089    private static final BigInteger INITIAL_VALUE = BigInteger.ONE;
090
091    /** Default allowed complexity. */
092    private static final int DEFAULT_COMPLEXITY_VALUE = 10;
093
094    /** Stack of values - all but the current value. */
095    private final Deque<BigInteger> valueStack = new ArrayDeque<>();
096
097    /** Control whether to treat the whole switch block as a single decision point. */
098    private boolean switchBlockAsSingleDecisionPoint;
099
100    /** The current value. */
101    private BigInteger currentValue = INITIAL_VALUE;
102
103    /** Specify the maximum threshold allowed. */
104    private int max = DEFAULT_COMPLEXITY_VALUE;
105
106    /**
107     * Setter to control whether to treat the whole switch block as a single decision point.
108     *
109     * @param switchBlockAsSingleDecisionPoint whether to treat the whole switch
110     *                                          block as a single decision point.
111     * @since 6.11
112     */
113    public void setSwitchBlockAsSingleDecisionPoint(boolean switchBlockAsSingleDecisionPoint) {
114        this.switchBlockAsSingleDecisionPoint = switchBlockAsSingleDecisionPoint;
115    }
116
117    /**
118     * Setter to specify the maximum threshold allowed.
119     *
120     * @param max the maximum threshold
121     * @since 3.2
122     */
123    public final void setMax(int max) {
124        this.max = max;
125    }
126
127    @Override
128    public int[] getDefaultTokens() {
129        return new int[] {
130            TokenTypes.CTOR_DEF,
131            TokenTypes.METHOD_DEF,
132            TokenTypes.INSTANCE_INIT,
133            TokenTypes.STATIC_INIT,
134            TokenTypes.LITERAL_WHILE,
135            TokenTypes.LITERAL_DO,
136            TokenTypes.LITERAL_FOR,
137            TokenTypes.LITERAL_IF,
138            TokenTypes.LITERAL_SWITCH,
139            TokenTypes.LITERAL_CASE,
140            TokenTypes.LITERAL_CATCH,
141            TokenTypes.QUESTION,
142            TokenTypes.LAND,
143            TokenTypes.LOR,
144            TokenTypes.COMPACT_CTOR_DEF,
145            TokenTypes.LITERAL_WHEN,
146        };
147    }
148
149    @Override
150    public int[] getAcceptableTokens() {
151        return new int[] {
152            TokenTypes.CTOR_DEF,
153            TokenTypes.METHOD_DEF,
154            TokenTypes.INSTANCE_INIT,
155            TokenTypes.STATIC_INIT,
156            TokenTypes.LITERAL_WHILE,
157            TokenTypes.LITERAL_DO,
158            TokenTypes.LITERAL_FOR,
159            TokenTypes.LITERAL_IF,
160            TokenTypes.LITERAL_SWITCH,
161            TokenTypes.LITERAL_CASE,
162            TokenTypes.LITERAL_CATCH,
163            TokenTypes.QUESTION,
164            TokenTypes.LAND,
165            TokenTypes.LOR,
166            TokenTypes.COMPACT_CTOR_DEF,
167            TokenTypes.LITERAL_WHEN,
168        };
169    }
170
171    @Override
172    public final int[] getRequiredTokens() {
173        return new int[] {
174            TokenTypes.CTOR_DEF,
175            TokenTypes.METHOD_DEF,
176            TokenTypes.INSTANCE_INIT,
177            TokenTypes.STATIC_INIT,
178            TokenTypes.COMPACT_CTOR_DEF,
179        };
180    }
181
182    @Override
183    public void visitToken(DetailAST ast) {
184        switch (ast.getType()) {
185            case TokenTypes.CTOR_DEF,
186                 TokenTypes.METHOD_DEF,
187                 TokenTypes.INSTANCE_INIT,
188                 TokenTypes.STATIC_INIT,
189                 TokenTypes.COMPACT_CTOR_DEF -> visitMethodDef();
190
191            default -> visitTokenHook(ast);
192        }
193    }
194
195    @Override
196    public void leaveToken(DetailAST ast) {
197        switch (ast.getType()) {
198            case TokenTypes.CTOR_DEF,
199                 TokenTypes.METHOD_DEF,
200                 TokenTypes.INSTANCE_INIT,
201                 TokenTypes.STATIC_INIT,
202                 TokenTypes.COMPACT_CTOR_DEF -> leaveMethodDef(ast);
203
204            default -> {
205                // Do nothing
206            }
207        }
208    }
209
210    /**
211     * Hook called when visiting a token. Will not be called the method
212     * definition tokens.
213     *
214     * @param ast the token being visited
215     */
216    private void visitTokenHook(DetailAST ast) {
217        if (switchBlockAsSingleDecisionPoint) {
218            if (!ScopeUtil.isInBlockOf(ast, TokenTypes.LITERAL_SWITCH)) {
219                incrementCurrentValue(BigInteger.ONE);
220            }
221        }
222        else if (ast.getType() != TokenTypes.LITERAL_SWITCH) {
223            incrementCurrentValue(BigInteger.ONE);
224        }
225    }
226
227    /**
228     * Process the end of a method definition.
229     *
230     * @param ast the token representing the method definition
231     */
232    private void leaveMethodDef(DetailAST ast) {
233        final BigInteger bigIntegerMax = BigInteger.valueOf(max);
234        if (currentValue.compareTo(bigIntegerMax) > 0) {
235            log(ast, MSG_KEY, currentValue, bigIntegerMax);
236        }
237        popValue();
238    }
239
240    /**
241     * Increments the current value by a specified amount.
242     *
243     * @param amount the amount to increment by
244     */
245    private void incrementCurrentValue(BigInteger amount) {
246        currentValue = currentValue.add(amount);
247    }
248
249    /** Push the current value on the stack. */
250    private void pushValue() {
251        valueStack.push(currentValue);
252        currentValue = INITIAL_VALUE;
253    }
254
255    /**
256     * Pops a value off the stack and makes it the current value.
257     */
258    private void popValue() {
259        currentValue = valueStack.pop();
260    }
261
262    /** Process the start of the method definition. */
263    private void visitMethodDef() {
264        pushValue();
265    }
266
267}