StringBuilder.insert, delete and replace are fairly expensive operations since they have to shift the everything past that point to make room or squeeze up. With replace, if the replacement String is the same length as the one replaced, you don’t have this problem.

To find out how many chars are in a StringBuilder altready use length( );

To reuse a StringBuilder use setLength( 0 );

If you know the precise length of the String you are building in advance, usually you can build it more efficiently with a char[] ca and use new String( ca ) to convert the result.

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