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 TYPECAST, METHOD_CALL, EXPR, ARRAY_INIT, UNARY_MINUS, UNARY_PLUS, ELIST, STAR, ASSIGN, PLUS, MINUS, DIV, LITERAL_NEW.
    • 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

    • Constructor Detail

      • MagicNumberCheck

        public MagicNumberCheck()
        Constructor for MagicNumber Check. Sort the allowedTokensBetweenMagicNumberAndConstDef array for binary search.

    • Method Detail

      • getDefaultTokens

        public int[] getDefaultTokens()
        Description copied from class: AbstractCheck
        Returns the default token a check is interested in. Only used if the configuration for a check does not define the tokens.
        Specified by:
        getDefaultTokens in class AbstractCheck
        Returns:
        the default tokens
        See Also:
        TokenTypes

      • 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

      • getRequiredTokens

        public int[] getRequiredTokens()
        Description copied from class: AbstractCheck
        The tokens that this check must be registered for.
        Specified by:
        getRequiredTokens in class AbstractCheck
        Returns:
        the token set this must be registered for.
        See Also:
        TokenTypes

      • 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 - list of 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