Magic number

Reports "magic numbers": numeric literals that are not named by a constant declaration.

Using magic numbers can lead to unclear code, as well as errors if a magic number is changed in one location but remains unchanged not another. The numbers 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 100, 1000, 0L, 1L, 2L, 0.0, 1.0, 0.0F and 1.0F are not reported by this inspection.

Example:

  void checkFileSize(long bytes) {
    if (bytes > 1_048_576) {
      throw new IllegalArgumentException("too big");
    }
  }

A quick-fix introduces a new constant:

  static final int MAX_SUPPORTED_FILE_SIZE = 1_048_576;

  void checkFileSize(long bytes) {
    if (bytes > MAX_SUPPORTED_FILE_SIZE) {
      throw new IllegalArgumentException("too big");
    }
  }

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

MagicNumber

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Java | Abstraction issues

Configure the inspection:

Use the Ignore constants in 'hashCode()' methods option to disable this inspection within hashCode() methods.
Use the Ignore in annotations option to ignore magic numbers in annotations.
Use the Ignore initial capacity for StringBuilders and Collections option to ignore magic numbers used as initial capacity when constructing Collection, Map, StringBuilder or StringBuffer objects.

Inspection options

Here you can find the description of settings available for the Magic number inspection, and the reference of their default values.

Ignore constants in 'hashCode()' methods: Default: Selected
Ignore in annotations: Default: Selected
Ignore initial capacity for StringBuilders and Collections: Not selected

Availability

By default bundled with: IntelliJ IDEA 2024.1, Qodana for JVM 2024.1,
Can be installed with plugin: Java, 241.18072

Last modified: 18 June 2024