Package com.puppycrawl.tools.checkstyle.checks.coding

Class MagicNumberCheck

  • All Implemented Interfaces:
    Configurable, Contextualizable
    public class MagicNumberCheck
extends AbstractCheck

    Checks that there are no "magic numbers" where a magic number is a numeric literal that is not defined as a constant. By default, -1, 0, 1, and 2 are not considered to be magic numbers.

    Constant definition is any variable/field that has 'final' modifier. It is fine to have one constant defining multiple numeric literals within one expression: 

     static final int SECONDS_PER_DAY = 24 * 60 * 60;
 static final double SPECIAL_RATIO = 4.0 / 3.0;
 static final double SPECIAL_SUM = 1 + Math.E;
 static final double SPECIAL_DIFFERENCE = 4 - Math.PI;
 static final Border STANDARD_BORDER = BorderFactory.createEmptyBorder(3, 3, 3, 3);
 static final Integer ANSWER_TO_THE_ULTIMATE_QUESTION_OF_LIFE = new Integer(42);
    • Property ignoreNumbers - Specify non-magic numbers. Type is double[]. Default value is -1, 0, 1, 2.
    • Property ignoreHashCodeMethod - Ignore magic numbers in hashCode methods. Type is boolean. Default value is false.
    • Property ignoreAnnotation - Ignore magic numbers in annotation declarations. Type is boolean. Default value is false.
    • Property ignoreFieldDeclaration - Ignore magic numbers in field declarations. Type is boolean. Default value is false.
    • Property ignoreAnnotationElementDefaults - Ignore magic numbers in annotation elements defaults. Type is boolean. Default value is true.
    • Property constantWaiverParentToken - Specify tokens that are allowed in the AST path from the number literal to the enclosing constant definition. Type is java.lang.String[]. Validation type is tokenTypesSet. Default value is ARRAY_INIT, ASSIGN, DIV, ELIST, EXPR, LITERAL_NEW, METHOD_CALL, MINUS, PLUS, STAR, TYPECAST, UNARY_MINUS, UNARY_PLUS.
    • Property tokens - tokens to check Type is java.lang.String[]. Validation type is tokenSet. Default value is: NUM_DOUBLE, NUM_FLOAT, NUM_INT, NUM_LONG.

    To configure the check with default configuration: 

     <module name="MagicNumber"/>

    results is following violations: 

     @MyAnnotation(6) // violation
 class MyClass {
   private field = 7; // violation

   void foo() {
     int i = i + 1; // no violation
     int j = j + 8; // violation
   }

   public int hashCode() {
     return 10;    // violation
   }
 }
 @interface anno {
   int value() default 10; // no violation
 }

    To configure the check so that it checks floating-point numbers that are not 0, 0.5, or 1: 

     <module name="MagicNumber">
   <property name="tokens" value="NUM_DOUBLE, NUM_FLOAT"/>
   <property name="ignoreNumbers" value="0, 0.5, 1"/>
   <property name="ignoreFieldDeclaration" value="true"/>
   <property name="ignoreAnnotation" value="true"/>
 </module>

    results is following violations: 

     @MyAnnotation(6) // no violation
 class MyClass {
   private field = 7; // no violation

   void foo() {
     int i = i + 1; // no violation
     int j = j + 8; // violation
   }
 }

    To configure the check so that it ignores magic numbers in field declarations: 

     <module name="MagicNumber">
   <property name="ignoreFieldDeclaration" value="false"/>
 </module>

    results in the following violations: 

     public record MyRecord() {
     private static int myInt = 7; // ok, field declaration

     void foo() {
         int i = myInt + 1; // no violation, 1 is defined as non-magic
         int j = myInt + 8; // violation
     }
 }

    To configure the check to check annotation element defaults: 

     <module name="MagicNumber">
   <property name="ignoreAnnotationElementDefaults" value="false"/>
 </module>

    results in following violations: 

     @interface anno {
   int value() default 10; // violation
   int[] value2() default {10}; // violation
 }

    Config example of constantWaiverParentToken option: 

     <module name="MagicNumber">
   <property name="constantWaiverParentToken" value="ASSIGN,ARRAY_INIT,EXPR,
   UNARY_PLUS, UNARY_MINUS, TYPECAST, ELIST, DIV, PLUS "/>
 </module>

    result is following violation: 

     class TestMethodCall {
   public void method2() {
     final TestMethodCall dummyObject = new TestMethodCall(62);    //violation
     final int a = 3;        // ok as waiver is ASSIGN
     final int [] b = {4, 5} // ok as waiver is ARRAY_INIT
     final int c = -3;       // ok as waiver is UNARY_MINUS
     final int d = +4;       // ok as waiver is UNARY_PLUS
     final int e = method(1, 2) // ELIST is there but violation due to METHOD_CALL
     final int x = 3 * 4;    // violation
     final int y = 3 / 4;    // ok as waiver is DIV
     final int z = 3 + 4;    // ok as waiver is PLUS
     final int w = 3 - 4;    // violation
     final int x = (int)(3.4);    //ok as waiver is TYPECAST
   }
 }

    Config example of ignoreHashCodeMethod option: 

     <module name="MagicNumber">
   <property name="ignoreHashCodeMethod" value="true"/>
 </module>

    result is no violation: 

     class TestHashCode {
     public int hashCode() {
         return 10;       // OK
     }
 }

    Parent is com.puppycrawl.tools.checkstyle.TreeWalker

    Violation Message Keys:

    • magic.number
    Since:
    3.1

    • Field Detail

      • MSG_KEY

        public static final java.lang.String MSG_KEY
        A key is pointing to the warning message text in "messages.properties" file.
        See Also:
        Constant Field Values

      • constantWaiverParentToken

        private java.util.BitSet constantWaiverParentToken
        Specify tokens that are allowed in the AST path from the number literal to the enclosing constant definition.

      • ignoreNumbers

        private double[] ignoreNumbers
        Specify non-magic numbers.

      • ignoreHashCodeMethod

        private boolean ignoreHashCodeMethod
        Ignore magic numbers in hashCode methods.

      • ignoreAnnotation

        private boolean ignoreAnnotation
        Ignore magic numbers in annotation declarations.

    • Method Detail

      • getAcceptableTokens

        public int[] getAcceptableTokens()
        Description copied from class: AbstractCheck
        The configurable token set. Used to protect Checks against malicious users who specify an unacceptable token set in the configuration file. The default implementation returns the check's default tokens.
        Specified by:
        getAcceptableTokens in class AbstractCheck
        Returns:
        the token set this check is designed for.
        See Also:
        TokenTypes

      • shouldTestAnnotationArgs

        private boolean shouldTestAnnotationArgs​(DetailAST ast)
        Checks if ast is annotation argument and should be checked.
        Parameters:
        ast - token to check
        Returns:
        true if element is skipped, false otherwise

      • shouldTestAnnotationDefaults

        private boolean shouldTestAnnotationDefaults​(DetailAST ast)
        Checks if ast is annotation element default value and should be checked.
        Parameters:
        ast - token to check
        Returns:
        true if element is skipped, false otherwise

      • isMagicNumberExists

        private boolean isMagicNumberExists​(DetailAST ast,
                                    DetailAST constantDefAST)
        Is magic number somewhere at ast tree.
        Parameters:
        ast - ast token
        constantDefAST - constant ast
        Returns:
        true if magic number is present

      • findContainingConstantDef

        private static DetailAST findContainingConstantDef​(DetailAST ast)
        Finds the constant definition that contains aAST.
        Parameters:
        ast - the AST
        Returns:
        the constant def or null if ast is not contained in a constant definition.

      • reportMagicNumber

        private void reportMagicNumber​(DetailAST ast)
        Reports aAST as a magic number, includes unary operators as needed.
        Parameters:
        ast - the AST node that contains the number to report

      • isInHashCodeMethod

        private static boolean isInHashCodeMethod​(DetailAST ast)
        Determines whether or not the given AST is in a valid hash code method. A valid hash code method is considered to be a method of the signature public int hashCode().
        Parameters:
        ast - the AST from which to search for an enclosing hash code method definition
        Returns:
        true if ast is in the scope of a valid hash code method.

      • isInIgnoreList

        private boolean isInIgnoreList​(DetailAST ast)
        Decides whether the number of an AST is in the ignore list of this check.
        Parameters:
        ast - the AST to check
        Returns:
        true if the number of ast is in the ignore list of this check.

      • isFieldDeclaration

        private static boolean isFieldDeclaration​(DetailAST ast)
        Determines whether or not the given AST is field declaration.
        Parameters:
        ast - AST from which to search for an enclosing field declaration
        Returns:
        true if ast is in the scope of field declaration

      • setConstantWaiverParentToken

        public void setConstantWaiverParentToken​(java.lang.String... tokens)
        Setter to specify tokens that are allowed in the AST path from the number literal to the enclosing constant definition.
        Parameters:
        tokens - The string representation of the tokens interested in

      • setIgnoreNumbers

        public void setIgnoreNumbers​(double... list)
        Setter to specify non-magic numbers.
        Parameters:
        list - numbers to ignore.

      • setIgnoreHashCodeMethod

        public void setIgnoreHashCodeMethod​(boolean ignoreHashCodeMethod)
        Setter to ignore magic numbers in hashCode methods.
        Parameters:
        ignoreHashCodeMethod - decide whether to ignore hash code methods

      • setIgnoreAnnotation

        public void setIgnoreAnnotation​(boolean ignoreAnnotation)
        Setter to ignore magic numbers in annotation declarations.
        Parameters:
        ignoreAnnotation - decide whether to ignore annotations

      • setIgnoreFieldDeclaration

        public void setIgnoreFieldDeclaration​(boolean ignoreFieldDeclaration)
        Setter to ignore magic numbers in field declarations.
        Parameters:
        ignoreFieldDeclaration - decide whether to ignore magic numbers in field declaration

      • setIgnoreAnnotationElementDefaults

        public void setIgnoreAnnotationElementDefaults​(boolean ignoreAnnotationElementDefaults)
        Setter to ignore magic numbers in annotation elements defaults.
        Parameters:
        ignoreAnnotationElementDefaults - decide whether to ignore annotation elements defaults

      • isChildOf

        private static boolean isChildOf​(DetailAST ast,
                                 int type)
        Determines if the given AST node has a parent node with given token type code.
        Parameters:
        ast - the AST from which to search for annotations
        type - the type code of parent token
        Returns:
        true if the AST node has a parent with given token type.