继承（开始）

extends 关键字

子类构造器特点

因为子类只继承了父类的成员&方法, 子类没有继承到父类的构造器,但是要求子类必须调用父类构造器

如果父类没有无参构造器子类创建时候会报错

a. 调用子类的无参&无参构造器,实际也默认先调用了父类的无参构造器

b. 如果父类没有无参构造器,子类必须显示的先调用父类的有参数构造器

//这里引出了super关键字 代表父类的引用

super("color", "name");

：super关键字的特点&使用

super:父类的引用,用于访问父类的属性,方法,构造器 语法

访问父类的属性: super.属性名=属性值

访问父类的方法:super.方法(实参列表)

访问父类的构造:super(实参列表)

 

package test1;

class Person{

     String name;

     charsex;

     intage;

     Person(String name,charsex,intage){

         this.name=name;

         this.sex=sex;

         this.age=age;

     }

     public String toString()

     {

         returnname+" "+sex+" "+age;

     }

}

class Student extends Person{

     longnumber;

     intmath;

     intenglish;

     intcomputer;

     public Student(String n,chars,inta,longnu,intm,inte,intc)

     {

         super(n,s,a);

         number=nu;

         math=m;

         english=e;

         computer=c;

     }

     publicdouble aver()

     {

     return (computer+math+english)/3;

     }

     publicint max()

     {

         inta;

         a=math>english? math:english;

         a=a>computer? a:computer;

         returna;

     }

     publicint min()

     {

         inta;

         a=math<english? math:english;

         a=a<computer? a:computer;

         returna;

     }

     public String toString()

     {

         return" "+number+" "+math+" "+english+" "+computer;

     }

}

publicclass Test {

     publicstaticvoid main(String[] args) {

     Person A =new Person("wangjingbo",'b',19);

     Student B = new Student("wangjingbo",'b',19,20203991,100,90,80);

     A.toString();

    System.out.println(A.toString()+B.toString());

    System.out.println("aver:"+B.aver()+" max:"+B.max()+" min:"+B.min());

     }

}