You now know how to create, inspect, search, transform, and build strings in Java. Strings are immutable objects, so every modification returns a new String rather than changing the original. Always use .equals() for comparison, not ==.
For performance-sensitive code that assembles text in a loop, use StringBuilder to avoid the time and space cost of repeated concatenation. And remember to validate before parsing with Integer.parseInt() or Double.parseDouble() to prevent runtime exceptions.