Source code

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 java.util.ArrayDeque;
023import java.util.Deque;
024
025import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
026import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
027import com.puppycrawl.tools.checkstyle.api.DetailAST;
028import com.puppycrawl.tools.checkstyle.api.TokenTypes;
029
030/**
031 * <p>
032 * Checks that there is only one statement per line.
033 * </p>
034 * <p>
035 * Rationale: It's very difficult to read multiple statements on one line.
036 * </p>
037 * <p>
038 * In the Java programming language, statements are the fundamental unit of
039 * execution. All statements except blocks are terminated by a semicolon.
040 * Blocks are denoted by open and close curly braces.
041 * </p>
042 * <p>
043 * OneStatementPerLineCheck checks the following types of statements:
044 * variable declaration statements, empty statements, import statements,
045 * assignment statements, expression statements, increment statements,
046 * object creation statements, 'for loop' statements, 'break' statements,
047 * 'continue' statements, 'return' statements, resources statements (optional).
048 * </p>
049 * <ul>
050 * <li>
051 * Property {@code treatTryResourcesAsStatement} - Enable resources processing.
052 * Default value is {@code false}.
053 * </li>
054 * </ul>
055 * <p>
056 * An example of how to configure this Check:
057 * </p>
058 * <pre>
059 * &lt;module name=&quot;OneStatementPerLine&quot;/&gt;
060 * </pre>
061 * <p>
062 * The following examples will be flagged as a violation:
063 * </p>
064 * <pre>
065 * //Each line causes violation:
066 * int var1; int var2;
067 * var1 = 1; var2 = 2;
068 * int var1 = 1; int var2 = 2;
069 * var1++; var2++;
070 * Object obj1 = new Object(); Object obj2 = new Object();
071 * import java.io.EOFException; import java.io.BufferedReader;
072 * ;; //two empty statements on the same line.
073 *
074 * //Multi-line statements:
075 * int var1 = 1
076 * ; var2 = 2; //violation here
077 * int o = 1, p = 2,
078 * r = 5; int t; //violation here
079 * </pre>
080 * <p>
081 * An example of how to configure the check to treat resources
082 * in a try statement as statements to require them on their own line:
083 * </p>
084 * <pre>
085 * &lt;module name=&quot;OneStatementPerLine&quot;&gt;
086 *   &lt;property name=&quot;treatTryResourcesAsStatement&quot; value=&quot;true&quot;/&gt;
087 * &lt;/module&gt;
088 * </pre>
089 * <p>
090 * Note: resource declarations can contain variable definitions
091 * and variable references (from java9).
092 * When property "treatTryResourcesAsStatement" is enabled,
093 * this check is only applied to variable definitions.
094 * If there are one or more variable references
095 * and one variable definition on the same line in resources declaration,
096 * there is no violation.
097 * The following examples will illustrate difference:
098 * </p>
099 * <pre>
100 * OutputStream s1 = new PipedOutputStream();
101 * OutputStream s2 = new PipedOutputStream();
102 * // only one statement(variable definition) with two variable references
103 * try (s1; s2; OutputStream s3 = new PipedOutputStream();) // OK
104 * {}
105 * // two statements with variable definitions
106 * try (Reader r = new PipedReader(); s2; Reader s3 = new PipedReader() // violation
107 * ) {}
108 * </pre>
109 *
110 * @since 5.3
111 */
112@FileStatefulCheck
113public final class OneStatementPerLineCheck extends AbstractCheck {
114
115    /**
116     * A key is pointing to the warning message text in "messages.properties"
117     * file.
118     */
119    public static final String MSG_KEY = "multiple.statements.line";
120
121    /**
122     * Counts number of semicolons in nested lambdas.
123     */
124    private final Deque<Integer> countOfSemiInLambda = new ArrayDeque<>();
125
126    /**
127     * Hold the line-number where the last statement ended.
128     */
129    private int lastStatementEnd = -1;
130
131    /**
132     * Hold the line-number where the last 'for-loop' statement ended.
133     */
134    private int forStatementEnd = -1;
135
136    /**
137     * The for-header usually has 3 statements on one line, but THIS IS OK.
138     */
139    private boolean inForHeader;
140
141    /**
142     * Holds if current token is inside lambda.
143     */
144    private boolean isInLambda;
145
146    /**
147     * Hold the line-number where the last lambda statement ended.
148     */
149    private int lambdaStatementEnd = -1;
150
151    /**
152     * Hold the line-number where the last resource variable statement ended.
153     */
154    private int lastVariableResourceStatementEnd = -1;
155
156    /**
157     * Enable resources processing.
158     */
159    private boolean treatTryResourcesAsStatement;
160
161    /**
162     * Setter to enable resources processing.
163     * @param treatTryResourcesAsStatement user's value of treatTryResourcesAsStatement.
164     */
165    public void setTreatTryResourcesAsStatement(boolean treatTryResourcesAsStatement) {
166        this.treatTryResourcesAsStatement = treatTryResourcesAsStatement;
167    }
168
169    @Override
170    public int[] getDefaultTokens() {
171        return getRequiredTokens();
172    }
173
174    @Override
175    public int[] getAcceptableTokens() {
176        return getRequiredTokens();
177    }
178
179    @Override
180    public int[] getRequiredTokens() {
181        return new int[] {
182            TokenTypes.SEMI,
183            TokenTypes.FOR_INIT,
184            TokenTypes.FOR_ITERATOR,
185            TokenTypes.LAMBDA,
186        };
187    }
188
189    @Override
190    public void beginTree(DetailAST rootAST) {
191        inForHeader = false;
192        lastStatementEnd = -1;
193        forStatementEnd = -1;
194        isInLambda = false;
195        lastVariableResourceStatementEnd = -1;
196    }
197
198    @Override
199    public void visitToken(DetailAST ast) {
200        switch (ast.getType()) {
201            case TokenTypes.SEMI:
202                checkIfSemicolonIsInDifferentLineThanPrevious(ast);
203                break;
204            case TokenTypes.FOR_ITERATOR:
205                forStatementEnd = ast.getLineNo();
206                break;
207            case TokenTypes.LAMBDA:
208                isInLambda = true;
209                countOfSemiInLambda.push(0);
210                break;
211            default:
212                inForHeader = true;
213                break;
214        }
215    }
216
217    @Override
218    public void leaveToken(DetailAST ast) {
219        switch (ast.getType()) {
220            case TokenTypes.SEMI:
221                lastStatementEnd = ast.getLineNo();
222                forStatementEnd = -1;
223                lambdaStatementEnd = -1;
224                break;
225            case TokenTypes.FOR_ITERATOR:
226                inForHeader = false;
227                break;
228            case TokenTypes.LAMBDA:
229                countOfSemiInLambda.pop();
230                if (countOfSemiInLambda.isEmpty()) {
231                    isInLambda = false;
232                }
233                lambdaStatementEnd = ast.getLineNo();
234                break;
235            default:
236                break;
237        }
238    }
239
240    /**
241     * Checks if given semicolon is in different line than previous.
242     * @param ast semicolon to check
243     */
244    private void checkIfSemicolonIsInDifferentLineThanPrevious(DetailAST ast) {
245        DetailAST currentStatement = ast;
246        final boolean hasResourcesPrevSibling =
247                currentStatement.getPreviousSibling() != null
248                        && currentStatement.getPreviousSibling().getType() == TokenTypes.RESOURCES;
249        if (!hasResourcesPrevSibling && isMultilineStatement(currentStatement)) {
250            currentStatement = ast.getPreviousSibling();
251        }
252        if (isInLambda) {
253            checkLambda(ast, currentStatement);
254        }
255        else if (isResource(ast.getParent())) {
256            checkResourceVariable(ast);
257        }
258        else if (!inForHeader && isOnTheSameLine(currentStatement, lastStatementEnd,
259                forStatementEnd, lambdaStatementEnd)) {
260            log(ast, MSG_KEY);
261        }
262    }
263
264    private void checkLambda(DetailAST ast, DetailAST currentStatement) {
265        int countOfSemiInCurrentLambda = countOfSemiInLambda.pop();
266        countOfSemiInCurrentLambda++;
267        countOfSemiInLambda.push(countOfSemiInCurrentLambda);
268        if (!inForHeader && countOfSemiInCurrentLambda > 1
269                && isOnTheSameLine(currentStatement,
270                lastStatementEnd, forStatementEnd,
271                lambdaStatementEnd)) {
272            log(ast, MSG_KEY);
273        }
274    }
275
276    private static boolean isResource(DetailAST ast) {
277        return ast != null
278            && (ast.getType() == TokenTypes.RESOURCES
279                 || ast.getType() == TokenTypes.RESOURCE_SPECIFICATION);
280    }
281
282    private void checkResourceVariable(DetailAST currentStatement) {
283        if (treatTryResourcesAsStatement) {
284            final DetailAST nextNode = currentStatement.getNextSibling();
285            if (currentStatement.getPreviousSibling().findFirstToken(TokenTypes.ASSIGN) != null) {
286                lastVariableResourceStatementEnd = currentStatement.getLineNo();
287            }
288            if (nextNode.findFirstToken(TokenTypes.ASSIGN) != null
289                && nextNode.getLineNo() == lastVariableResourceStatementEnd) {
290                log(currentStatement, MSG_KEY);
291            }
292        }
293    }
294
295    /**
296     * Checks whether two statements are on the same line.
297     * @param ast token for the current statement.
298     * @param lastStatementEnd the line-number where the last statement ended.
299     * @param forStatementEnd the line-number where the last 'for-loop'
300     *                        statement ended.
301     * @param lambdaStatementEnd the line-number where the last lambda
302     *                        statement ended.
303     * @return true if two statements are on the same line.
304     */
305    private static boolean isOnTheSameLine(DetailAST ast, int lastStatementEnd,
306                                           int forStatementEnd, int lambdaStatementEnd) {
307        return lastStatementEnd == ast.getLineNo() && forStatementEnd != ast.getLineNo()
308                && lambdaStatementEnd != ast.getLineNo();
309    }
310
311    /**
312     * Checks whether statement is multiline.
313     * @param ast token for the current statement.
314     * @return true if one statement is distributed over two or more lines.
315     */
316    private static boolean isMultilineStatement(DetailAST ast) {
317        final boolean multiline;
318        if (ast.getPreviousSibling() == null) {
319            multiline = false;
320        }
321        else {
322            final DetailAST prevSibling = ast.getPreviousSibling();
323            multiline = prevSibling.getLineNo() != ast.getLineNo()
324                    && ast.getParent() != null;
325        }
326        return multiline;
327    }
328
329}