The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
Question: What is wrong with the following interface:
public interface House { @Deprecated public void open(); public void openFrontDoor(); public void openBackDoor(); }
Answer The documentation should reflect why open
is deprecated and what to use instead. For example:
public interface House { /** * @deprecated use ofopen
* is discouraged, use *openFrontDoor
or *openBackDoor
instead. */ @Deprecated public void open(); public void openFrontDoor(); public void openBackDoor(); }
Question: 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 produces a warning because open
was deprecated (in the interface). What can you do to get rid of that warning?
Answer: 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() {} }
Will the following code compile without error? Why or why not?
public @interface Meal { ... } @Meal("breakfast", mainDish="cereal") @Meal("lunch", mainDish="pizza") @Meal("dinner", mainDish="salad") public void evaluateDiet() { ... }
Answer: The code fails to compile. Before JDK 8, repeatable annotations are not supported. As of JDK 8, the code fails to compile because the Meal
annotation type was not defined to be repeatable. It can be fixed by adding the @Repeatable
meta-annotation and defining a container annotation type:
public class AnnotationTest { public @interface MealContainer { Meal[] value(); } @java.lang.annotation.Repeatable(MealContainer.class) public @interface Meal { String value(); String mainDish(); } @Meal(value="breakfast", mainDish="cereal") @Meal(value="lunch", mainDish="pizza") @Meal(value="dinner", mainDish="salad") public void evaluateDiet() { } }
id
, synopsis
, engineer
, and date
. Specify the default value as unassigned
for engineer and unknown
for date.
Answer:
/** * Describes the Request-for-Enhancement (RFE) annotation type. */ public @interface RequestForEnhancement { int id(); String synopsis(); String engineer() default "[unassigned]"; String date() default "[unknown]"; }