Answers to Questions and Exercises: Annotations - Java Tutorial 5.0 英文版

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Trail: Learning the Java Language
Lesson: Classes and Inheritance

Answers to Questions and Exercises: Annotations

Questions

Question 1: What is wrong with the following inteface:
public interface House {
    @Deprecated
    public void open();
    public void openFrontDoor();
    public void openBackDoor();
}
Answer 1:The documentation should reflect why open is deprecated and what to use instead. For example:
public interface House { 
    /**
     * @deprecated use of open is discouraged, use
     * openFrontDoor or openBackDoor instead.
     */
    @Deprecated
    public void open(); 
    public void openFrontDoor();
    public void openBackDoor();
}
Question 2: Compile this program:
interface Closable {
    void close();
}

class File implements Closable {
    @Override
    public void close() {
        //... close this file...
    }
}
What happens? Can you explain why?
Answer 2: The compiler generates an error complaining that File.close doesn't override any method from its superclass. This is because it is not overriding Closable.close, it is implementing it!
Question 3: Consider this implementation of the House interface, shown in Question 1.
public class MyHouse implements House {
    public void open() {}
    public void openFrontDoor() {}
    public void openBackDoor() {}
}
If you compile this program, the compiler complains that open has been deprecated (in the interface). What can you do to get rid of that warning?
Answer 3: You can deprecate the implementation of open:
public class MyHouse implements House { 
    //The documentation is inherited from the interface.
    @Deprecated
    public void open() {} 
    public void openFrontDoor() {}
    public void openBackDoor() {}
}
Alternatively, you can suppress the warning:
public class MyHouse implements House { 
    @SuppressWarnings("deprecation")
    public void open() {} 
    public void openFrontDoor() {}
    public void openBackDoor() {}
}

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