001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2026 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 applied to methods, c-tors,
037 * <a href="https://docs.oracle.com/javase/tutorial/java/javaOO/initial.html">
038 * static initializers and instance initializers</a>.
039 * </div>
040 *
041 * <p>
042 * The complexity is equal to the number of decision points {@code + 1}.
043 * Decision points:
044 * </p>
045 * <ul>
046 * <li>
047 * {@code if}, {@code while}, {@code do}, {@code for},
048 * {@code ?:}, {@code catch}, {@code switch}, {@code case} statements.
049 * </li>
050 * <li>
051 *  Operators {@code &&} and {@code ||} in the body of target.
052 * </li>
053 * <li>
054 *  {@code when} expression in case labels, also known as guards.
055 * </li>
056 * </ul>
057 *
058 * <p>
059 * By pure theory level 1-4 is considered easy to test, 5-7 OK, 8-10 consider
060 * re-factoring to ease testing, and 11+ re-factor now as testing will be painful.
061 * </p>
062 *
063 * <p>
064 * When it comes to code quality measurement by this metric level 10 is very
065 * good level as a ultimate target (that is hard to archive). Do not be ashamed
066 * to have complexity level 15 or even higher, but keep it below 20 to catch
067 * really bad-designed code automatically.
068 * </p>
069 *
070 * <p>
071 * Please use Suppression to avoid violations on cases that could not be split
072 * in few methods without damaging readability of code or encapsulation.
073 * </p>
074 *
075 * @since 3.2
076 */
077@FileStatefulCheck
078public class CyclomaticComplexityCheck extends AbstractCheck {
079
080    /**
081     * A key is pointing to the warning message text in "messages.properties" file.
082     */
083    public static final String MSG_KEY = "cyclomaticComplexity";
084
085    /** The initial current value. */
086    private static final BigInteger INITIAL_VALUE = BigInteger.ONE;
087
088    /** Default allowed complexity. */
089    private static final int DEFAULT_COMPLEXITY_VALUE = 10;
090
091    /** Stack of values - all but the current value. */
092    private final Deque<BigInteger> valueStack = new ArrayDeque<>();
093
094    /** Control whether to treat the whole switch block as a single decision point. */
095    private boolean switchBlockAsSingleDecisionPoint;
096
097    /** The current value. */
098    private BigInteger currentValue = INITIAL_VALUE;
099
100    /** Specify the maximum threshold allowed. */
101    private int max = DEFAULT_COMPLEXITY_VALUE;
102
103    /**
104     * Creates a new {@code CyclomaticComplexityCheck} instance.
105     */
106    public CyclomaticComplexityCheck() {
107        // no code by default
108    }
109
110    /**
111     * Setter to control whether to treat the whole switch block as a single decision point.
112     *
113     * @param switchBlockAsSingleDecisionPoint whether to treat the whole switch
114     *                                          block as a single decision point.
115     * @since 6.11
116     */
117    public void setSwitchBlockAsSingleDecisionPoint(boolean switchBlockAsSingleDecisionPoint) {
118        this.switchBlockAsSingleDecisionPoint = switchBlockAsSingleDecisionPoint;
119    }
120
121    /**
122     * Setter to specify the maximum threshold allowed.
123     *
124     * @param max the maximum threshold
125     * @since 3.2
126     */
127    public final void setMax(int max) {
128        this.max = max;
129    }
130
131    @Override
132    public int[] getDefaultTokens() {
133        return new int[] {
134            TokenTypes.CTOR_DEF,
135            TokenTypes.METHOD_DEF,
136            TokenTypes.INSTANCE_INIT,
137            TokenTypes.STATIC_INIT,
138            TokenTypes.LITERAL_WHILE,
139            TokenTypes.LITERAL_DO,
140            TokenTypes.LITERAL_FOR,
141            TokenTypes.LITERAL_IF,
142            TokenTypes.LITERAL_SWITCH,
143            TokenTypes.LITERAL_CASE,
144            TokenTypes.LITERAL_CATCH,
145            TokenTypes.QUESTION,
146            TokenTypes.LAND,
147            TokenTypes.LOR,
148            TokenTypes.COMPACT_CTOR_DEF,
149            TokenTypes.LITERAL_WHEN,
150        };
151    }
152
153    @Override
154    public int[] getAcceptableTokens() {
155        return new int[] {
156            TokenTypes.CTOR_DEF,
157            TokenTypes.METHOD_DEF,
158            TokenTypes.INSTANCE_INIT,
159            TokenTypes.STATIC_INIT,
160            TokenTypes.LITERAL_WHILE,
161            TokenTypes.LITERAL_DO,
162            TokenTypes.LITERAL_FOR,
163            TokenTypes.LITERAL_IF,
164            TokenTypes.LITERAL_SWITCH,
165            TokenTypes.LITERAL_CASE,
166            TokenTypes.LITERAL_CATCH,
167            TokenTypes.QUESTION,
168            TokenTypes.LAND,
169            TokenTypes.LOR,
170            TokenTypes.COMPACT_CTOR_DEF,
171            TokenTypes.LITERAL_WHEN,
172        };
173    }
174
175    @Override
176    public final int[] getRequiredTokens() {
177        return new int[] {
178            TokenTypes.CTOR_DEF,
179            TokenTypes.METHOD_DEF,
180            TokenTypes.INSTANCE_INIT,
181            TokenTypes.STATIC_INIT,
182            TokenTypes.COMPACT_CTOR_DEF,
183        };
184    }
185
186    @Override
187    public void beginTree(DetailAST rootAST) {
188        valueStack.clear();
189        currentValue = INITIAL_VALUE;
190    }
191
192    @Override
193    public void visitToken(DetailAST ast) {
194        switch (ast.getType()) {
195            case TokenTypes.CTOR_DEF,
196                 TokenTypes.METHOD_DEF,
197                 TokenTypes.INSTANCE_INIT,
198                 TokenTypes.STATIC_INIT,
199                 TokenTypes.COMPACT_CTOR_DEF -> visitMethodDef();
200
201            default -> visitTokenHook(ast);
202        }
203    }
204
205    @Override
206    public void leaveToken(DetailAST ast) {
207        switch (ast.getType()) {
208            case TokenTypes.CTOR_DEF,
209                 TokenTypes.METHOD_DEF,
210                 TokenTypes.INSTANCE_INIT,
211                 TokenTypes.STATIC_INIT,
212                 TokenTypes.COMPACT_CTOR_DEF -> leaveMethodDef(ast);
213
214            default -> {
215                // Do nothing
216            }
217        }
218    }
219
220    /**
221     * Hook called when visiting a token. Will not be called the method definition tokens.
222     *
223     * @param ast the token being visited
224     */
225    private void visitTokenHook(DetailAST ast) {
226        if (switchBlockAsSingleDecisionPoint) {
227            if (!ScopeUtil.isInBlockOf(ast, TokenTypes.LITERAL_SWITCH)) {
228                incrementCurrentValue(BigInteger.ONE);
229            }
230        }
231        else if (ast.getType() != TokenTypes.LITERAL_SWITCH) {
232            incrementCurrentValue(BigInteger.ONE);
233        }
234    }
235
236    /**
237     * Process the end of a method definition.
238     *
239     * @param ast the token representing the method definition
240     */
241    private void leaveMethodDef(DetailAST ast) {
242        final BigInteger bigIntegerMax = BigInteger.valueOf(max);
243        if (currentValue.compareTo(bigIntegerMax) > 0) {
244            log(ast, MSG_KEY, currentValue, bigIntegerMax);
245        }
246        popValue();
247    }
248
249    /**
250     * Increments the current value by a specified amount.
251     *
252     * @param amount the amount to increment by
253     */
254    private void incrementCurrentValue(BigInteger amount) {
255        currentValue = currentValue.add(amount);
256    }
257
258    /** Push the current value on the stack. */
259    private void pushValue() {
260        valueStack.push(currentValue);
261        currentValue = INITIAL_VALUE;
262    }
263
264    /**
265     * Pops a value off the stack and makes it the current value.
266     */
267    private void popValue() {
268        currentValue = valueStack.pop();
269    }
270
271    /** Process the start of the method definition. */
272    private void visitMethodDef() {
273        pushValue();
274    }
275
276}