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30 */
31 package com.qulice.checkstyle;
32
33 import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
34 import com.puppycrawl.tools.checkstyle.api.DetailAST;
35 import com.puppycrawl.tools.checkstyle.api.TokenTypes;
36 import java.util.LinkedList;
37 import java.util.List;
38
39 /**
40 * Checks for not using concatenation of string literals in any form.
41 *
42 * <p>The following constructs are prohibited:
43 *
44 * <pre>
45 * String a = "done in " + time + " seconds";
46 * System.out.println("File not found: " + file);
47 * x += "done";
48 * </pre>
49 *
50 * <p>You should avoid string concatenation at all cost. Why? There are two
51 * reasons: readability of the code and translateability. First of all it's
52 * difficult to understand how the text will look after concatenation,
53 * especially if the text is long and there are more than a few {@code +}
54 * operators. Second, you won't be able to translate your text to other
55 * languages later, if you don't have solid string literals.
56 *
57 * <p>There are two alternatives to concatenation: {@link StringBuilder}
58 * and {@link String#format(String,Object[])}.
59 *
60 * @since 0.3
61 */
62 public final class StringLiteralsConcatenationCheck extends AbstractCheck {
63
64 @Override
65 public int[] getDefaultTokens() {
66 return new int[] {TokenTypes.OBJBLOCK};
67 }
68
69 @Override
70 public int[] getAcceptableTokens() {
71 return this.getDefaultTokens();
72 }
73
74 @Override
75 public int[] getRequiredTokens() {
76 return this.getDefaultTokens();
77 }
78
79 @Override
80 public void visitToken(final DetailAST ast) {
81 final List<DetailAST> pluses = this.findChildAstsOfType(
82 ast,
83 TokenTypes.PLUS,
84 TokenTypes.PLUS_ASSIGN
85 );
86 for (final DetailAST plus : pluses) {
87 if (!this.findChildAstsOfType(
88 plus,
89 TokenTypes.STRING_LITERAL
90 ).isEmpty()) {
91 this.log(plus, "Concatenation of string literals prohibited");
92 }
93 }
94 }
95
96 /**
97 * Recursively traverse the <code>tree</code> and return all ASTs subtrees
98 * matching any type from <code>types</code>.
99 * @param tree AST to traverse.
100 * @param types Token types to match against.
101 * @return All ASTs subtrees with token types matching any from
102 * <tt>types</tt>.
103 * @see TokenTypes
104 */
105 private List<DetailAST> findChildAstsOfType(final DetailAST tree,
106 final int... types) {
107 final List<DetailAST> children = new LinkedList<>();
108 DetailAST child = tree.getFirstChild();
109 while (child != null) {
110 if (StringLiteralsConcatenationCheck.isOfType(child, types)) {
111 children.add(child);
112 } else {
113 children.addAll(this.findChildAstsOfType(child, types));
114 }
115 child = child.getNextSibling();
116 }
117 return children;
118 }
119
120 /**
121 * Checks if this <code>ast</code> is of any type from <code>types</code>.
122 * @param ast AST to check.
123 * @param types Token types to match against.
124 * @return True if of type, false otherwise.
125 * @see TokenTypes
126 */
127 private static boolean isOfType(final DetailAST ast, final int... types) {
128 boolean yes = false;
129 for (final int type : types) {
130 if (ast.getType() == type) {
131 yes = true;
132 break;
133 }
134 }
135 return yes;
136 }
137 }