Annotation Interface MagicConstant


This annotation intended to help IntelliJ IDEA and other IDEs to detect and auto-complete int and String constants used as an enumeration. For example, in the Label(String, int) constructor the alignment parameter can be one of the following int constants: Label.LEFT, Label.CENTER or Label.RIGHT

So, if @MagicConstant annotation applied to this constructor, the IDE will check the constructor usages for the allowed values.

E.g.


 new Label("text", 0); // 0 is not allowed
 new Label("text", Label.LEFT); // OK
 

@MagicConstant can be applied to:

  • Field, local variable, parameter.
    E.g.
    @MagicConstant(intValues = {TOP, CENTER, BOTTOM})
     int textPosition;
     
    The IDE will check expressions assigned to the variable for allowed values:
    
      textPosition = 0; // not allowed
      textPosition = TOP; // OK
     
  • Method
    E.g.
    @MagicConstant(flagsFromClass = java.lang.reflect.Modifier.class)
      public native int getModifiers();
     
    The IDE will analyse getModifiers() method calls and check if its return value is used with allowed values:
    
      if (aClass.getModifiers() == 3) // not allowed
      if (aClass.getModifiers() == Modifier.PUBLIC) // OK
     
  • Annotation class
    Annotation class annotated with @MagicConstant created alias you can use to annotate everything as if it was annotated with @MagicConstant itself.
    E.g.
    @MagicConstant(flags = {Font.PLAIN, Font.BOLD, Font.ITALIC}) 
    @interface FontStyle {} 
    The IDE will check constructs annotated with @FontStyle for allowed values:
    @FontStyle int myStyle = 3; // not allowed
    @FontStyle int myStyle = Font.BOLD | Font.ITALIC; // OK
The @MagicConstant annotation has SOURCE retention, i.e. it is removed upon compilation and does not create any runtime overhead.
  • Element Details

    • intValues

      long[] intValues
      Returns:
      int values (typically named constants) which are allowed here. E.g.
       
       void setConfirmOpenNewProject(@MagicConstant(intValues = {OPEN_PROJECT_ASK, OPEN_PROJECT_NEW_WINDOW, OPEN_PROJECT_SAME_WINDOW})
                                     int confirmOpenNewProject);
       
      Default:
      {}
    • stringValues

      @NonNls @NonNls String[] stringValues
      Returns:
      String values (typically named constants) which are allowed here.
      Default:
      {}
    • flags

      long[] flags
      Returns:
      allowed int flags (i.e. values (typically named constants) which can be combined with bitwise OR operator (|). The difference from the intValues() is that flags are allowed to be combined (via plus:+ or bitwise OR: |) whereas values aren't. The literals "0" and "-1" are also allowed to denote absence and presense of all flags respectively. E.g.
       @MagicConstant(flags = {HierarchyEvent.PARENT_CHANGED,HierarchyEvent.DISPLAYABILITY_CHANGED,HierarchyEvent.SHOWING_CHANGED})
       int hFlags;
      
       hFlags = 3; // not allowed; should be "magic" constant.
       if (hFlags & (HierarchyEvent.PARENT_CHANGED | HierarchyEvent.SHOWING_CHANGED) != 0); // OK: combined several constants via bitwise OR
       
      Default:
      {}
    • valuesFromClass

      Class<?> valuesFromClass
      Returns:
      allowed values which are defined in the specified class static final constants. E.g.
       @MagicConstant(valuesFromClass = Cursor.class)
       int cursorType;
      
       cursorType = 11; // not allowed; should be "magic" constant.
       cursorType = Cursor.E_RESIZE_CURSOR; // OK: "magic" constant used.
       
      Default:
      void.class
    • flagsFromClass

      Class<?> flagsFromClass
      Returns:
      allowed int flags which are defined in the specified class static final constants. The difference from the valuesFromClass() is that flags are allowed to be combined (via plus:+ or bitwise OR: |) whereas values aren't. The literals "0" and "-1" are also allowed to denote absence and presense of all flags respectively. E.g.
       @MagicConstant(flagsFromClass = java.awt.InputEvent.class)
       int eventMask;
      
       eventMask = 10; // not allowed; should be "magic" constant.
       eventMask = InputEvent.CTRL_MASK | InputEvent.ALT_MASK; // OK: combined several constants via bitwise OR
       
      Default:
      void.class