How to replace all characters in a Java string with stars

Java 11 and later

str = "*".repeat(str.length());

Note: This replaces newlines \n with *. If you want to preserve \n, see solution below.

Java 10 and earlier

str = str.replaceAll(".", "*");

This preserves newlines.

To replace newlines with * as well in Java 10 and earlier, you can use:

str = str.replaceAll("(?s).", "*");

The (?s) doesn’t match anything but activates DOTALL mode which makes . also match \n.