replaceFirst()

Example

Substitute the initial occurrence of a regular expression match with a distinct substring.

String myStr = "This is W3Schools";
String regex = "is";
System.out.println(myStr.replaceFirst(regex, "at"));

Definition and Usage

The replaceFirst() method in Java replaces the initial match of a regular expression within a string with a new substring.

In replacement strings, you can include a backreference as $n, where n represents the index of a group in the pattern. In the resulting string, occurrences of $n will be substituted with the substring matched by the respective group. Alternatively, using $0 will replace it with the entire expression. Refer to “More Examples” below for an illustration of using a backreference.

Hint: Consult the Java RegEx tutorial to grasp regular expressions.

Syntax

Parameter Values

Technical Details

More Examples

Example

Employ a backreference to enclose the initial number within parentheses.

String myStr = "Quest complete! Earned 30 gold and 500 experience.";
String regex = "[0-9]+";
System.out.println(myStr.replaceFirst(regex, "($0)"));