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Trail: Learning the Java Language
Lesson: Object-Oriented Programming Concepts
Home Page > Learning the Java Language > Object-Oriented Programming Concepts
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# Answers to Questions and Exercises: Object-Oriented Programming Concepts

## Answers to Questions

1. Real-world objects contain state and behavior.
2. A software object's state is stored in fields.
3. A software object's behavior is exposed through methods.
4. Hiding internal data from the outside world, and accessing it only through publicly exposed methods is known as data encapsulation.
5. A blueprint for a software object is called a class.
6. Common behavior can be defined in a superclass and inherited into a subclass using the extends keyword.
7. A collection of methods with no implementation is called an interface.
8. A namespace that organizes classes and interfaces by functionality is called a package.
9. The term API stands for Application Programming Interface.

### Answers to Exercises

1. Your answers will vary depending on the real-world objects that you are modeling.
2. Your answers will vary here as well, but the error message will specifically list the required methods that have not been implemented.

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