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There are many situations: encrypting and decrypting text, file format conversion, text formatters, and others. Many Java String methods such as trim() create a new string based on an old string.


In physics, a transducer is a device that converts one form of energy to another. For example, a photocell is a transducer because it converts light energy into electrical energy. The transducers in this chapter convert one type of string into another type of string.

A finite-state transducer (FST) is an automaton where the state transitions are labeled with:

  1. The symbols that cause the state transition. (This is just like an automaton.)
  2. An action to perform as the transition is made.

A FST has both an input string and an output string. The actions that are performed during a state transition create the output string.

A series of actions that a program performs could be considered an "output string". For example, the program that controls your microwave oven is almost certainly a finite-state transducer. Its input string is the sequence of actions you perform on its controls. Its output string is a series of signals that control the various oven components.


What does the toUpperCase() method of the Java String class do?