JAVA Interface

1、西安电子科技大学软件学院 刘惠,Interface,西安电子科技大学软件学院 刘惠,Agender,What is Interface? How to Create Interface? Interface Vs. Class Interfaces Modifier How to Use Interfer? “Multiple inheritance” in Java Extending an interface with inheritance Grouping constants,西安电子科技大学软件学院 刘惠,What is Interface?,An interface says: “

2、This is what all classes that implement this particular interface will look like.” Thus, any code that uses a particular interface knows what methods might be called for that interface. The interface is used to establish a “protocol” between classes.,西安电子科技大学软件学院 刘惠,How to Create Interface?,To creat

3、e an interface, use the interface keyword instead of the class keyword.,modifier interface interface_name variableType variableName1; variableType variableName2; returnType method1( paras); returnType method2( paras); ,西安电子科技大学软件学院 刘惠,Interface Vs. Class,An interface provides only a form (method nam

4、es, argument lists, and return types), but no method bodies (no implementation). An interface can also contain fields, but these are implicitly static and final.,西安电子科技大学软件学院 刘惠,Interfaces Modifier,Modifier before interface: Like a class, you can add the public keyword before the interface keyword (

5、but only if that interface is defined in a file of the same name) or leave it off to give “friendly” status so that it is only usable within the same package.,西安电子科技大学软件学院 刘惠,Interfaces Modifier,Modifier before method: You can choose to explicitly declare the method declarations in an interface as p

6、ublic. But they are public even if you dont say it.,西安电子科技大学软件学院 刘惠,Interfaces Modifier,Modifier before attribute: An interface can also contain fields, but these are implicitly static and final. The fields in an interface are automatically public .,西安电子科技大学软件学院 刘惠,How to Use Interfer,To make a clas

7、s that conforms to a particular interface (or group of interfaces) use the implements keyword.,西安电子科技大学软件学院 刘惠,First Exaple,Music5.java,西安电子科技大学软件学院 刘惠,“Multiple inheritance” in Java,there is no storage associated with an interfacetheres nothing to prevent many interfaces from being combined. This i

8、s valuable because there are times when you need to say “An x is an a and a b and a c.”,西安电子科技大学软件学院 刘惠,“Multiple inheritance” in Java,西安电子科技大学软件学院 刘惠,Example,Adventure.java,西安电子科技大学软件学院 刘惠,Question1,In above example, if I update code like this , then what will we get?,class Hero implements CanFight

9、, CanSwim, CanFly extends ActionCharacter public void swim() System.out.println(Swin); public void fly() System.out.println(fly); ,西安电子科技大学软件学院 刘惠,Question2,In above example, if I update code like this , then what will we get?,class Hero extends ActionCharacter implements CanFight, CanSwim, CanFly p

10、ublic void swim() System.out.println(Swin); / public void fly() System.out.println(fly); ,西安电子科技大学软件学院 刘惠,Question3,In above example, if I update code like this , then what will we get?,class Hero extends ActionCharacter implements CanFight, CanSwim, CanFly public void swim() System.out.println(Swin

11、); public void fly() System.out.println(fly); public void fight() System.out.println(fight); /add a line ,西安电子科技大学软件学院 刘惠,Extending an interface with inheritance,You can easily add new method declarations to an interface using inheritance ,you can combine several interfaces into a new interface with inheritance . HorrorShow.java,西安电子科技大学软件学院 刘惠,Grouping constants,Because any fields you put into an interface are automatically static and final, the interface is a convenient tool for creating groups of constant values, much as you would with an enum in C or C+. See an example：,public interf