Feature Request: Recipe to Extract Magic Numbers to Type-and-Value-Named Constants per Class#769
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boraciner wants to merge 9 commits intoopenrewrite:mainfrom
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Introduce `ReplaceMagicNumbersWithConstants` recipe implementing Sonar rule java:S109. This recipe extracts numeric literals from method bodies into private static final constants to improve code readability and maintainability. Also add `ReplaceMagicNumbersWithConstantsTest` with test cases verifying: - constants are generated for numeric literals - literals already assigned to variables or fields are ignored - replacements preserve correctness and type consistency
-1, 0, and 1 are not considered magic numbers.
-1, 0, and 1 are not considered magic numbers.
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src/main/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstants.java
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src/main/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstants.java
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src/main/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstants.java
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src/main/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstants.java
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src/main/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstants.java
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src/main/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstants.java
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src/main/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstants.java
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src/test/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstantsTest.java
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src/test/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstantsTest.java
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timtebeek
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Nov 3, 2025
src/main/java/org/openrewrite/staticanalysis/ReplaceMagicNumbersWithConstants.java
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| import org.openrewrite.*; | ||
| import org.openrewrite.java.JavaTemplate; |
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| import org.openrewrite.*; | |
| import org.openrewrite.java.JavaTemplate; | |
| import org.openrewrite.Cursor; | |
| import org.openrewrite.ExecutionContext; | |
| import org.openrewrite.Recipe; | |
| import org.openrewrite.TreeVisitor; | |
| import java.util.ArrayList; | |
| import java.util.HashSet; | |
| import java.util.List; | |
| import java.util.Set; | |
| import static java.util.Collections.singleton; |
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| public @NlsRewrite.DisplayName String getDisplayName() { | ||
| return "Replace magic numbers with constants"; | ||
| } | ||
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| @Override | ||
| public @NlsRewrite.Description String getDescription() { | ||
| return "Replaces magic number literals in method bodies with named constants to improve code readability and maintainability. " |
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| public @NlsRewrite.DisplayName String getDisplayName() { | |
| return "Replace magic numbers with constants"; | |
| } | |
| @Override | |
| public @NlsRewrite.Description String getDescription() { | |
| return "Replaces magic number literals in method bodies with named constants to improve code readability and maintainability. " | |
| public String getDisplayName() { | |
| public String getDescription() { | |
| return "Replaces magic number literals in method bodies with named constants to improve code readability and maintainability. " + | |
| "Magic numbers are replaced by private static final constants declared at the top of the class, following Sonar's java:S109 rule. " + | |
| "The recipe does not create constants for literals that are already assigned to fields or variables, nor for typical non-magic numbers (such as 0, 1, or -1). " + | |
| "Currently, only numeric primitive literals are handled; string and character literals are unaffected. " + | |
| "If a constant for a value already exists, or the constant name would conflict with an existing symbol, the recipe will skip that value."; |
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| if (!(cursor.getParent().getParent().getValue() instanceof J.VariableDeclarations.NamedVariable) | ||
| && !isIgnoredMagicNumber(literal)) { | ||
| literals.add(literal); |
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| if (!(cursor.getParent().getParent().getValue() instanceof J.VariableDeclarations.NamedVariable) | |
| && !isIgnoredMagicNumber(literal)) { | |
| literals.add(literal); | |
| if (!(cursor.getParent().getParent().getValue() instanceof J.VariableDeclarations.NamedVariable) && | |
| !isIgnoredMagicNumber(literal)) { |
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| grandparent.getValue() instanceof J.VariableDeclarations.NamedVariable) | ||
| || isIgnoredMagicNumber(literal)) { |
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| grandparent.getValue() instanceof J.VariableDeclarations.NamedVariable) | |
| || isIgnoredMagicNumber(literal)) { | |
| grandparent.getValue() instanceof J.VariableDeclarations.NamedVariable) || | |
| isIgnoredMagicNumber(literal)) { |
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| private String printCursorPath(Cursor cursor) { | ||
| StringBuilder sb = new StringBuilder(); | ||
| while (cursor != null) { | ||
| Object val = cursor.getValue(); | ||
| sb.append(val == null ? "null" : val.getClass().getSimpleName()); | ||
| sb.append(" > "); | ||
| cursor = cursor.getParent(); | ||
| } | ||
| sb.append("ROOT"); | ||
| return sb.toString(); | ||
| } | ||
| @Override |
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| private String printCursorPath(Cursor cursor) { | |
| StringBuilder sb = new StringBuilder(); | |
| while (cursor != null) { | |
| Object val = cursor.getValue(); | |
| sb.append(val == null ? "null" : val.getClass().getSimpleName()); | |
| sb.append(" > "); | |
| cursor = cursor.getParent(); | |
| } | |
| sb.append("ROOT"); | |
| return sb.toString(); | |
| } | |
| @Override | |
| return singleton("RSPEC-109"); |
| private String getStrValFromLiteral(J.Literal literal) { | ||
| String type = getTypeName(literal).toUpperCase(); | ||
| String valueSource = literal.getValueSource(); | ||
| if (valueSource == null) return null; |
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| if (valueSource == null) return null; | |
| if (valueSource == null) { | |
| return null; | |
| } |
| } | ||
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| private String getTypeName(J.Literal literal) { | ||
| if (literal.getType() == null) return "Object"; |
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| if (literal.getType() == null) return "Object"; | |
| if (literal.getType() == null) { | |
| return "Object"; | |
| } |
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| import org.openrewrite.java.JavaParser; | ||
| import org.openrewrite.test.RecipeSpec; |
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| import org.openrewrite.java.JavaParser; | |
| import org.openrewrite.test.RecipeSpec; | |
| class ReplaceMagicNumbersWithConstantsTest implements RewriteTest { |
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| @DocumentExample | ||
| @Test |
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| @DocumentExample | |
| @Test | |
| @Test |
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| } | ||
| @DocumentExample |
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| } | |
| @DocumentExample | |
| } |
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This PR is stale because it has been open for 90 days with no activity. Remove |
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Introduce
ReplaceMagicNumbersWithConstantsrecipe implementing Sonar rule java:S109. This recipe extracts numeric literals from method bodies into private static final constants to improve code readability and maintainability.Also add
ReplaceMagicNumbersWithConstantsTestwith test cases verifying:What's changed?
Added new recipe: ReplaceMagicNumbersWithConstants
Added new test class: ReplaceMagicNumbersWithConstantsTest
What's your motivation?
To enhance code quality and readability by enforcing Sonar rule java:S109, reducing the use of magic numbers in Java code.
Anything in particular you'd like reviewers to focus on?
Verify correct handling of numeric literals and naming of generated constants
Confirm no false positives for literals already assigned to variables or fields
Ensure the recipe integrates cleanly with existing static analysis infrastructure
Have you considered any alternatives or workarounds?
Manual refactoring or partial Sonar-based analysis, but these approaches lack the automation and reproducibility provided by this recipe.