DecimalFormat

DecimalFormat is a concrete subclass of NumberFormat used to format decimal numbers according to a pattern, with awareness of locale-specific symbols. It is part of the java.text package in the Java standard library. A DecimalFormat instance formats numbers to produce human‑readable strings and can also parse strings back into numbers.

Pattern syntax lies at the core of DecimalFormat. The pattern uses 0 as a required digit and # as an optional digit. The decimal separator is a dot in the pattern, and the grouping separator is a comma. A semicolon can separate positive and negative subpatterns. Exponent notation can be requested with E or e. Percent and per‑mille symbols scale the number by 100 or 1/1000, respectively. Text can be included literally by enclosing it in single quotes. Patterns may be customized with literals and multiple sections, and can be supplied to the constructor or set via methods.

DecimalFormat relies on DecimalFormatSymbols to provide locale‑specific symbols such as the decimal separator, grouping separator, percent sign, and currency sign. It supports various configuration options, including setMinimumFractionDigits, setMaximumFractionDigits, setMinimumIntegerDigits, and setGroupingUsed. It also offers setGroupingSize for grouping behavior. For parsing, parse can return a Number, and setParseBigDecimal(true) makes parsing yield a BigDecimal. Formatting and parsing respect the locale unless overridden.

Thread safety is not guaranteed; instances should be confined to a single thread or protected by synchronization. Related classes include DecimalFormatSymbols and NumberFormat.