Method return values in Java enable methods to produce results for the caller. Using 'returnType methodName()', where returnType specifies what the method produces, and 'return value;' sends the result back. For example, 'int sum(int a, int b) { return a + b; }' returns the sum. The calling code can use the result: 'int total = sum(5, 3);'. Return types can be primitives, objects, or void (no return). Understanding return values enables you to create methods that compute and provide results.

Mastering return values enables you to create query methods and functional-style operations. Being able to return computed results is fundamental to implementing calculations, transformations, and queries. In professional development, return values appear constantly: getter methods, calculations, factory methods, and queries. For example, 'getTotal()' returns a calculated value, while 'findUser(id)' returns a found object. Methods with return values are pure (don't modify state) and easier to test and reason about than methods with side effects.

By learning return values effectively, you'll design methods that are testable, composable, and clear in intent. Understanding when to return values versus modify state is crucial for good design. This knowledge is fundamental to functional programming concepts in Java. Prerequisites include understanding methods, types, and expressions in Java.