Mask some part of String

Phone:

String replaced = yourString.replaceAll("\\b(\\d{2})\\d+(\\d)", "$1*******$2");

Email:

String replaced = yourString.replaceAll("\\b(\\w)[^@]+@\\S+(\\.[^\\s.]+)", "$1***@****$2");

Explanation: phone

• The \b boundary helps check that we are the start of the digits (there are other ways to do this, but here this will do).
• (\d{2}) captures two digits to Group 1 (the two first digits)
• \d+ matches any number of digits
• (\d) captures the final digit to Group 2
• In the replacement, $1 and $2 contain the content matched by Groups 1 and 2

Explanation: Email

• The \b boundary helps check that we are the start of the characters (there are other ways to do this, but here this will do).
• (\w) captures one word char to Group 1
• [^@]+ matches one or more chars that are not @
• \S+ matches one or more chars that are not whitespace chars
• (\.[^\s.]+) captures a dot and any chars that are not a dot or space to Group 2
• In the replacement, $1 and $2 contain the content matched by Groups 1 and 2