1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2026 the original author or authors.
4 //
5 // This library is free software; you can redistribute it and/or
6 // modify it under the terms of the GNU Lesser General Public
7 // License as published by the Free Software Foundation; either
8 // version 2.1 of the License, or (at your option) any later version.
9 //
10 // This library is distributed in the hope that it will be useful,
11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 // Lesser General Public License for more details.
14 //
15 // You should have received a copy of the GNU Lesser General Public
16 // License along with this library; if not, write to the Free Software
17 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18 ///////////////////////////////////////////////////////////////////////////////////////////////
19
20 package com.puppycrawl.tools.checkstyle.checks.imports;
21
22 import java.util.HashSet;
23 import java.util.Set;
24
25 import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
26 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
27 import com.puppycrawl.tools.checkstyle.api.DetailAST;
28 import com.puppycrawl.tools.checkstyle.api.FullIdent;
29 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
30
31 /**
32 * <div>
33 * Checks for redundant import statements. An import statement is
34 * considered redundant if:
35 * </div>
36 * <ul>
37 * <li>It is a duplicate of another import. This is, when a class or a module
38 * is imported more than once.</li>
39 * <li>The class non-statically imported is from the {@code java.lang}
40 * package, e.g. importing {@code java.lang.String}.</li>
41 * <li>The class non-statically imported is from the same package as the
42 * current package.</li>
43 * </ul>
44 *
45 * @since 3.0
46 */
47 @FileStatefulCheck
48 public class RedundantImportCheck
49 extends AbstractCheck {
50
51 /**
52 * A key is pointing to the warning message text in "messages.properties"
53 * file.
54 */
55 public static final String MSG_LANG = "import.lang";
56
57 /**
58 * A key is pointing to the warning message text in "messages.properties"
59 * file.
60 */
61 public static final String MSG_SAME = "import.same";
62
63 /**
64 * A key is pointing to the warning message text in "messages.properties"
65 * file.
66 */
67 public static final String MSG_DUPLICATE = "import.duplicate";
68
69 /** Set of the imports. */
70 private final Set<FullIdent> imports = new HashSet<>();
71 /** Set of static and module imports. */
72 private final Set<FullIdent> staticAndModuleImports = new HashSet<>();
73
74 /** Name of package in file. */
75 private String pkgName;
76
77 /**
78 * Creates a new {@code RedundantImportCheck} instance.
79 */
80 public RedundantImportCheck() {
81 // no code by default
82 }
83
84 @Override
85 public void beginTree(DetailAST aRootAST) {
86 pkgName = null;
87 imports.clear();
88 staticAndModuleImports.clear();
89 }
90
91 @Override
92 public int[] getDefaultTokens() {
93 return getRequiredTokens();
94 }
95
96 @Override
97 public int[] getAcceptableTokens() {
98 return getRequiredTokens();
99 }
100
101 @Override
102 public int[] getRequiredTokens() {
103 return new int[] {
104 TokenTypes.IMPORT,
105 TokenTypes.STATIC_IMPORT,
106 TokenTypes.PACKAGE_DEF,
107 TokenTypes.MODULE_IMPORT,
108 };
109 }
110
111 @Override
112 public void visitToken(DetailAST ast) {
113 if (ast.getType() == TokenTypes.PACKAGE_DEF) {
114 pkgName = FullIdent.createFullIdent(
115 ast.getLastChild().getPreviousSibling()).getText();
116 }
117 else if (ast.getType() == TokenTypes.IMPORT) {
118 final FullIdent imp = FullIdent.createFullIdentBelow(ast);
119 final String importText = imp.getText();
120 if (isFromPackage(importText, "java.lang")) {
121 log(ast, MSG_LANG, importText);
122 }
123 // imports from unnamed package are not allowed,
124 // so we are checking SAME rule only for named packages
125 else if (pkgName != null && isFromPackage(importText, pkgName)) {
126 log(ast, MSG_SAME, importText);
127 }
128 // Check for a duplicate import
129 imports.stream().filter(full -> importText.equals(full.getText()))
130 .forEach(full -> log(ast, MSG_DUPLICATE, full.getLineNo(), importText));
131
132 imports.add(imp);
133 }
134 else {
135 // Check for a duplicate static or module import
136 final DetailAST identNode = ast.getLastChild().getPreviousSibling();
137 final FullIdent importFullIdent = FullIdent.createFullIdent(identNode);
138 final String importText = importFullIdent.getText();
139
140 staticAndModuleImports
141 .stream()
142 .filter(existingImport -> importText.equals(existingImport.getText()))
143 .forEach(existingImport -> {
144 log(ast, MSG_DUPLICATE, existingImport.getLineNo(), importText);
145 });
146
147 staticAndModuleImports.add(importFullIdent);
148 }
149 }
150
151 /**
152 * Determines if an import statement is for types from a specified package.
153 *
154 * @param importName the import name
155 * @param pkg the package name
156 * @return whether from the package
157 */
158 private static boolean isFromPackage(String importName, String pkg) {
159 // imports from unnamed package are not allowed:
160 // https://docs.oracle.com/javase/specs/jls/se7/html/jls-7.html#jls-7.5
161 // So '.' must be present in member name and we are not checking for it
162 final int index = importName.lastIndexOf('.');
163 final String front = importName.substring(0, index);
164 return pkg.equals(front);
165 }
166
167 }