java练习册--类的继承.doc

文件编号：YM/WI-19文件版本： A版文件页码：page of java课程实践指导书JAVA篇 JAVA语言中的类的继承一、练习目标:掌握类的继承的一般方法。二、练习时间与作业要求：本次练习一共需要180分钟。翻译练习写在JAVA笔记本上，书面作业写在JAVA家庭作业本上。后面的书面作业不包括在这个时间范围内。三、翻译练习：将下面要求翻译的内容，写在记事本上Understanding Inheritance A subclass inherits variables and methods from its superclass and all of its ancestors. The subclass can use these members as is, or it can hide the member variables or override the methods. What Members Does a Subclass Inherit?Rule: A subclass inherits all of the members in its superclass that are accessible to that subclass unless the subclass explicitly hides a member variable or overrides a method. Note that constructors are not members and are not inherited by subclasses. The following list itemizes the members that are inherited by a subclass: Subclasses inherit those superclass members declared as public or protected. Subclasses inherit those superclass members declared with no access specifier as long as the subclass is in the same package as the superclass. Subclasses dont inherit a superclasss member if the subclass declares a member with the same name. In the case of member variables, the member variable in the subclass hides the one in the superclass. In the case of methods, the method in the subclass overrides the one in the superclass. Creating a subclass can be as simple as including the extends clause in your class declaration. However, you usually have to make other provisions in your code when subclassing a class, such as overriding methods or providing implementations for abstract methods. Hiding Member VariablesAs mentioned in the previous section, member variables defined in the subclass hide member variables that have the same name in the superclass. While this feature of the Java language is powerful and convenient, it can be a fruitful source of errors. When naming your member variables, be careful to hide only those member variables that you actually wish to hide. One interesting feature of Java member variables is that a class can access a hidden member variable through its superclass. Consider the following superclass and subclass pair: class Super Number aNumber;class Subbie extends Super Float aNumber;The aNumber variable in Subbie hides aNumber in Super. But you can access Supers aNumber from Subbie with super.aNumbersuper is a Java language keyword that allows a method to refer to hidden variables and overridden methods of the superclass. 四、上机练习：1、修改人类，增加一个静态的属性和和两个静态方法，并做如下测试：1）在静态方法中分别访问该类的静态与非静态属性2）在静态方法中分别访问该类的静态与非静态方法3）在非静态方法中分别访问该类的静态属性与方法4）在测试类的main方法直接去引用该类的属性与方法，看能使用哪些属性与方法？5）实例化一个该类，看还能不能通过该类的对象对访问它的静态方法6）实例化两个该类的对象，通过一个对象将类的静态属性改变，看一个另一个对象的该属性有没有改变。2、修改人类，在其中增加一个输出该人信息的方法printInfo()，修改学生类,包含学号属性格式为：前四位代表入学日期后四位是学生的编号，覆盖人类printInfo()方法，并提供一个自己的方法getInDate(String id)能通过