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");
  }
}

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

Option	Type	Default
Ignore constants in 'hashCode()' methods	Checkbox	true
Ignore in annotations	Checkbox	true
Ignore initial capacity for StringBuilders and Collections	Checkbox	false

Inspection Details
Available in:	IntelliJ IDEA 2023.3, Qodana for JVM 2023.3
Plugin:	Java, 233.SNAPSHOT

Last modified: 13 July 2023