Java面向对象的类与继承实例

class Original{ private int Orig_i; private String Orig_str; public Original(int Orig_i,String Orig_str) { this.Orig_i = Orig_i; this.Orig_str = Orig_str; } } public class Inherit extends Original { private String In_str; public Inherit() { super(20,"hello"); } //我们可以通过 super 关键字调用基类的带参数的构造方法 } */ class Original { protected int Orig_i; protected String Orig_str; public Original() { Orig_i = 0; Orig_str = ""; } public Original(int Orig_i,String Orig_str) { this.Orig_i = Orig_i; this.Orig_str = Orig_str; } } public class Inherit extends Original { private String In_str; public Inherit() { super(); } public Inherit(int Orig_i,String Orig_str)
public static void main(String[] args) { new C().displayA(); new C().displayB(); new C().displayC(); } } /** * 3,子类继承父类所有的成员变量和成员方法，但不继承父类的构造方法。
* 在子类的构造方法中可使用语句 super(参数列表) 调用父类的构造方法。 * 4,如果子类的构造方法中没有显式地调用父类构造方法，也没有使用 this 关键字调用重载 的其它构造方法， * 则在产生子类的实例对象时，系统默认调用父类无参数的构造方法。 */ /* 默认构造方法 class Original{ private int Orig_i; private String Orig_str; //public Original() {} //当我们没有为基类添加构造方法时,编译器将自动为编译器添加一个 默认的构造方法. } public class Inherit extends Original { private String In_str; //public Inherit() { super(); }//此时,子类的默认构造方法将自动添加一个 super()方法来调用 基类的默认构造方法. } */ /* 带参数的构造方法 class Original{ private int Orig_i; private String Orig_str; public Original(int Orig_i,String Orig_str) { this.Orig_i = Orig_i; this.Orig_str = Orig_str; } } public class Inherit extends Original { private String In_str; public Inherit() {} //当我们在基类手动添加了一个带参数的构造方法,这时编译器将不再为我们创建不带参数 的构造方法, //由于,类的继承不能继承构造方法,所以运行时会报错--缺少无参的构造方法! } */ /* 使用 super 调用基类构造方法.
以上通过一个类的继承的实例来为大家讲解面 向 对 象——类 与继承的实例关系。
private String school; public String setSchool(String school){this.school = school; return school;} public void study() { System.out.println("study in " + school); }
Person p2 = new Student(); p2.setName("mike"); p2.setAge(23); ((Student)p2).setSchool("Cambridge"); p2.getInfo(); ((Student)p2).study(); //父类的对象可以向下转型.
} */ /** * 1,通过继承可以简化类的定义 。 */ class Student extends Person //通过继承,这些重复的定义将被省略. { private String school; public String setSchool(String school){this.school = school; return school;} public void study() {
/* output from Inherit main() Orig_i = 0, Orig_str = , In_str = null Orig_i = 2, Orig_str = Original, In_str = null Orig_i = 3, Orig_str = Original, In_str = Inherit */
Student s1 = new Student(); s1.setName("jackson");s1.setAge(24);s1.setSchool("Oxford"); s1.getInfo(); s1.study();
/*但不能向上转型 Student s2 = (Student)new Person(); s2.setName("jane");s2.setAge(22);s2.setSchool("Cambridge"); s2.getInfo(); s2.study(); */ } } /** * 2,Java 只支持单根继承，不允许多重继承。 * 可以有多层继承，即一个类可以继承某一个类的子类，如类 B 继承了类 A，类 C 又可以 继承类 B，那么类 C 也间接继承了类 A。 */ class A { public void displayA() { System.out.println("class A is calling..."); } } class B extends A { public void displayB() { displayA();System.out.println("class B is calling..."); } } //class C extends B,A{}//类 C 不能同时继承类 A 和类 B class C extends B { public void displayC(){ displayB();System.out.println("class C is calling..."); }
/* output from C main() class A is calling... class A is calling... class B is calling... class A is calling... class B is calling...
class C is calling... */
System.out.println("study in " + school); }
public static void main(String[] args) { Person p1 = new Person(); p1.setName("unknown");p1.setAge(0); //p1.setSchool("unknown");错误,父类不能访问子类的成员. p1.getInfo(); //p1.study();错误,父类不能访问子类的成员.
Java 面向பைடு நூலகம்象的类与继承实例
/** * 类的继承 */ class Person { private String name; private int age; public String setName(String name){ = name;return name;} public int setAge(int age){this.age = age;return age;} public void getInfo() { System.out.println("name = " + name + ", age = " + age); } } /* class Student //Student 类重复定义了 Person 类的方法和成员变量 { private String name; private int age; public String setName(String name){ = name;return name;} public int setAge(int age){this.age = age;return age;} public void getInfo() { System.out.println("name = " + name + ", age = " + age); }
{ super(Orig_i,Orig_str); } public Inherit(int Orig_i,String Orig_str,String In_str) { this(Orig_i,Orig_str); //super(Orig_i,Orig_str); //也可以用 super 调用基类的构造方法,也可以通过 this 调用子类的重载的构造方法. this.In_str = In_str; } public void getInfo() { System.out.println("Orig_i = " + Orig_i + ", Orig_str = " + Orig_str + ", In_str = " + In_str); } public static void main(String[] args) { new Inherit().getInfo(); new Inherit(2,"Original").getInfo(); new Inherit(3,"Original","Inherit").getInfo(); } } /* output from Student main() name = unknown, age = 0 name = mike, age = 23 study in Cambridge name = jackson, age = 24 study in Oxford */