001 Source-code-from-the-lesson
https://github.com/AndriiPiatakha/learnit_java_core/tree/master/src/com/itbulls/learnit/javacore/string/stringbuilder

002 Source-code-examples-from-the-lesson
https://github.com/AndriiPiatakha/learnit_java_core/tree/master/src/com/itbulls/learnit/javacore/optional

003 Source-code-examples-from-the-lesson
https://github.com/AndriiPiatakha/learnit_java_core/commit/d62a11591550fc4c8455d610c8ddbcf31c194b71