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Trail: Learning the Java Language
Lesson: Interfaces and Inheritance
Interfaces and Inheritance
Interfaces
Defining an Interface
Implementing an Interface
Using an Interface as a Type
Rewriting Interfaces
Summary of Interfaces
Questions and Exercises
Inheritance
Overriding and Hiding Methods
Hiding Fields
Using the Keyword super
Object as a Superclass
Writing Final Classes and Methods
Abstract Methods and Classes
Summary of Inheritance
Questions and Exercises
Home Page > Learning the Java Language > Interfaces and Inheritance
Questions and Exercises: Interfaces

> ### Questions

> 1. What methods would a class that implements the `java.lang.CharSequence` interface have to implement?

> 2. What is wrong with the following interface?

>    >     public interface SomethingIsWrong {
>    >         void aMethod(int aValue){
>    >             System.out.println("Hi Mom");
>    >         }
>    >     }

> 3. Fix the interface in question 2.

> 4. Is the following interface valid?

>    >     public interface Marker {
>    >     }

> ### Exercises

> 1. Write a class that implements the `CharSequence` interface found in the `java.lang` package. Select one of the sentences from this book to use as the data. Write a small `main` method to test your class; make sure to call all four methods.

> 2. Suppose you have written a time server that periodically notifies its clients of the current date and time. Write an interface the server could use to enforce a particular protocol on its clients.

> Check your answers.

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