1903021114-胡静-JAVA第11周作业-JAVA中的继承,多态和抽象类
项目 | 内容 |
课程班级博客链接 | 19级信计班(本) |
这个作业要求链接 | 第11周作业 |
博客名称 | 1903021114-胡静-Java第十一周作业-java的继承多态和抽象类 |
要求 | 每道题要有题目,代码(使用插入代码,不会插入代码的自己查资料解决,不要直接截图代码!!),截图(只截运行结果) |
题目1:
类Person定义了姓名name,出生年份birthYear,其子类Graduate在继承父类的基础上新增定义了成绩gpa、毕业年份graduateYear。编写测试类,输出毕业生的姓名、年龄、毕业年份、成绩。
提示:父类要有构造方法,子类通过super调用父类构造方法。
代码:
父类person
package week11hj;
public class person {
public String name;
public double birthYear;
public person(String name, double birthYear) {
super();
this.name = name;
this.birthYear = birthYear;
}
public String getMessage() {
return "姓名:" +name;
}
}
子类graduate:
package week11hj;
public class gradute extends person {
int gpa;
int graduateYear;
int nowYear;
public gradute(String name, double birthYear, int graduateYear, int gpa, int nowYear) {
super(name, birthYear);
// TODO Auto-generated constructor stub
this.nowYear = nowYear;
this.gpa = gpa;
this.graduateYear = graduateYear;
}
public String getMessage() {
return super.getMessage()+"\n毕业年份:"+graduateYear+"\n成绩:"+gpa;
}
public double age() {
double nowYear = 2022;
return nowYear-birthYear;
}
}
测试类:
package week11hj;
public class test {
public static void main(String[] args) {
// TODO Auto-generated method stub
gradute g = new gradute("小明",2000,2023,98,2022);
System.out.println("毕业生信息为:"+g.getMessage());
System.out.println("年龄为:"+g.age());
}
}
截图:
题目2:
- 定义一个基本类Shape,有一个draw方法,定义三个类Circle(圆)、Triangle(三角形)、Square(正方形)都继承于Shape。在测试类中定义一个方法doStuff,传入基本类shape为参数,并调用draw方法。使用父类Shape创建三个类Circle、 Triangle、Square的实例对象并分别作为参数传入draw方法中。
- 提示:多态
代码:
Shape类:
package edu.xinji.week11;
public class Shape {
void draw() {}
}
Circle(圆)
package edu.xinji.week11;
public class Circle extends Shape {
void draw() {
System.out.println("Circle.draw()");
}
}
Triangle(三角形)
package edu.xinji.week11;
public class Triangle extends Shape {
void draw() {
System.out.println("Triangle.draw");
}
}
Square(正方形)
package edu.xinji.week11;
public class Square extends Shape {
void draw() {
System.out.println("Square.draw");
}
}
截图:
题目3:
-
所有的动物都有一个父类Animal,再定义两个子类Bird(鸟)和Dog(狗)继承自Animal,并实现父类中的bark(叫唤)方法。
- 提示:抽象
代码:
Animal:
package week11hj;
public abstract class Animal {
public abstract void bark();
}
Bird:
package week11hj;
public class Bird extends Animal {
@Override
public void bark() {
// TODO Auto-generated method stub
System.out.println("小鸟的叫声:啾啾");
}
}
Dog1:
package week11hj;
public class Dog1 extends Animal {
@Override
public void bark() {
// TODO Auto-generated method stub
System.out.println("小狗的叫声是:汪汪");
}
}
测试类:
package week11hj;
public class Test1 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Animal b = new Bird();
Animal d = new Dog1();
b.bark();
d.bark();
}
}
截图:
题目4:
-
不同几何图形的面积计算公式是不一样的,可是,它们具有的特性是一样的,都具有长和宽这两个属性,也都具有面积计算的方法。根据抽象的概念计算长方形的面积和三角形的面积。
- 提示:抽象
代码:
Shape:
package week11hj;
public abstract class Shape {
public int width;
public int height;
public Shape(int width, int height) {
super();
this.width = width;
this.height = height;
}
public abstract double area();
}
Square:
package week11hj;
public class Square extends Shape {
public Square(int width, int height) {
super(width, height);
// TODO Auto-generated constructor stub
}
public double area() {
return width*height;
}
}
Triangle:
package week11hj;
public class Triangle1 extends Shape {
public Triangle1(int width, int height) {
super(width, height);
// TODO Auto-generated constructor stub
}
public double area() {
return 0.5*width*height;
}
}
Test:
package week11hj;
public class Test2 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Shape s = new Square(6,8);
System.out.println("正方形面积为:"+s.area());
Triangle1 t = new Triangle1(6,8);
System.out.println("三角形面积为:"+t.area());
}
}
截图:
心得体会:
1、 在已经存在的类的基础上进行扩充和改造,形成一个新的类。满足“is a”的关系就是继承
2、多态是一种事务,多种形态。用名字一样的代码根据要求的不同,干不一样的事情。
分类
(1)对象的多态:父对象引用指向子类实例
(2)方法的多态:分为方法的重载和重写或者覆盖
3、重载是发生在同一类中,函数的名字相同,但是函数的参数个数,和参数类型,只要不一样,就是重载。
4、函数重写: 重写发生在两个类中,父类的方法,在子类中重新写。重写的函数名字和参数列表完全一样。重写的函数只能抛出比之前更小的异常。访问权限只能比之前的更大。