Java程序设计TR-Java-lecture07-interface.pptVIP

Java程序设计 Java Programming Fall, 2010 Contents Single vs. Multiple Inheritance Abstract Classes Interface Single vs. Multiple Inheritance Some object-oriented languages (eg.: C++) allow multiple(多重的) inheritance, which allows a class to be derived from two or more classes, inheriting the members of all parents; The price(代价): collisions(冲突), such as the same variable name, same method name in two parents, have to be resolved; Single vs. Multiple Inheritance Java decision: single inheritance for classes, meaning that a derived class can have only one parent class; However, in most cases, the use of interfaces(接口) gives us aspects of multiple inheritance without the overhead (will discuss later). Abstract Classes（抽象类） An abstract class is a conceptual class，表示的是“is-a”关系. abstract class provides a common root for a group of classes－－共性; use the modifier abstract on a class header to declare an abstract class: abstract class className { …… } Abstract Classes(抽象类) 实例化－由类创建对象/实例. An abstract class cannot be instantiated (实例化) – objects cannot be created; 它只能做为父类使用，由它派生的子类必须实现抽象类中所有的抽象方法，才能创建对象。 在abstract class 中可以有自己的数据成员，也可以有非abstarct的成员方法。 Abstract Classes (抽象类) An abstract class often contains abstract methods, though it doesn’t have to Abstract methods consist of only methods declarations, without any method body. When a class contains one or more abstract methods, it should be declared as abstract class; The abstract methods of an abstract class must be defined in its subclass; We cannot declare abstract constructors or abstract static methods. Abstract Classes //Animal.java public abstract class Animal { public String name; public int age; public void print() { Sytln(名字:+name); Sytln(大小:+age); } public abstract void run(); public abstract void cry(); } Abstract Classes (抽象类) public class AAnimal //错误 { public String name; public int age; public void print() { Sytln(名字:+name); Sytln(大小:+age); } public abstract void run(); pu