java 类的继承和多态 1

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1，设计一个抽象类，声明有关算术运算的方法，并创建一个子类继承该抽象的类，完成有理数的加、减、乘、除四则运算。

package a;public class YouLiShu {    int fz,fm;    public YouLiShu(){}    public YouLiShu(int fz, int fm) {        int ys=this.maxYueShu(fz, fm);              this.fz = fz/ys;        this.fm = fm/ys;    }       public YouLiShu jia(YouLiShu a){        int newfz=this.fz*a.fm+this.fm*a.fz;        int newfm=this.fm*a.fm;             return new YouLiShu(newfz/maxYueShu(newfz,newfm),newfm/maxYueShu(newfz,newfm));    }    public YouLiShu jian(YouLiShu a){                       int newfz=this.fz*a.fm-this.fm*a.fz;        int newfm=this.fm*a.fm;             return new YouLiShu(newfz/maxYueShu(newfz,newfm),newfm/maxYueShu(newfz,newfm));    }    public YouLiShu cheng(YouLiShu a){        int newfz=this.fz*a.fz;        int newfm=this.fm*a.fm;         return new YouLiShu(newfz/maxYueShu(newfz,newfm),newfm/maxYueShu(newfz,newfm));    }    public YouLiShu chu(YouLiShu a){        int newfz=this.fz*a.fm;        int newfm=this.fm*a.fz;             return new YouLiShu(newfz/maxYueShu(newfz,newfm),newfm/maxYueShu(newfz,newfm));    }    public String toString() {        return(fz+"/"+fm);    }    public double toXiaoShu(){              return (this.fz*(1.0))/this.fm;    }    public int maxYueShu(int a,int b){          if (b==0) return a;         return maxYueShu(b,a%b);    }}package a;public class Testsy1 {    public static void main(String[] args) {        YouLiShu y1=new YouLiShu(2,4);        YouLiShu y2=new YouLiShu(2,5);        System.out.println("2/4+2/5="+y1.jia(y2).toString()+" "+y1.jia(y2).toXiaoShu());        System.out.println("2/4-2/5="+y1.jian(y2).toString()+" "+y1.jian(y2).toXiaoShu());        System.out.println("2/4*2/5="+y1.cheng(y2).toString()+" "+y1.cheng(y2).toXiaoShu());        System.out.println("2/4 / 2/5="+y1.chu(y2).toString()+" "+y1.chu(y2).toXiaoShu());    }}

2，编写一个ComputerAverage抽象类，类中有一个抽象方法求平均分average，可以有参数。定义Gymnastics类和School类，它们都是ComputerAverage的子类，Gymnastics类中计算选手的平均成绩的方法是去掉一个最低分，去掉一个最高分，然后求平均分。School中计算平均分的方法是直接是总分除以总科目。
要求：定义ComputerAverage的对象为上转型对象，并调用重写的方法averge。

package b;public abstract class ComputerAverage {    public abstract double average(double[] s);}package shiyan3;public class Gymnastics extends ComputerAverage{    public double average(double s[]) {        for(int i=0;i<s.length-1;i++)        {            for(int j=i;j<s.length-1;j++)            {                if(s[i]>s[i+1])                {                    double t=s[i];                    s[i]=s[i+1];                    s[i+1]=t;                }            }        }        double a=0.0;        for(int i=1;i<s.length-1;i++)        {            a+=s[i];        }        a=a/(s.length-2);        return a;    }}package b;public class School extends ComputerAverage{    public double average(double s[]) {        double a=0.0;        for(int i=0;i<s.length;i++)        {            a+=s[i];        }        a=a/(s.length);        return a;    }}package b;public class Testsy3 {    public static void main(String[] args) {        double[] c={2.2,3.4,5.6,6.2,1.4};        ComputerAverage a=new Gymnastics();        ComputerAverage b=new School();        System.out.println(a.average(c));        System.out.println(b.average(c));    }}

3,编写一个类，该类有如下一个方法：
public int f(int a,int b){……//要求该方法将返回a和b的最大公约数}，再编写一个该类的子类，要求子类重写方法f()，而且重写的方法将返回两个正整数的最小公倍数。
要求：在重写的方法的方法体中需要调用被隐藏的方法返回a和b的最大公约数m，然后将（a*b/m）返回；在应用的程序的主类中分别使用父类和子类创建对象，并分别调用方法f（）计算两个正整数的最大公约数和最小公倍数。

package c;public class Maxgys {    int a;    int b;    Maxgys(int a,int b){        this.a=a;        this.b=b;    }    int f(){        int m=a;        int n=b;        if(m<n)        {            int t=n;            n=m;            m=t;        }        while(m%n!=0)        {            int t=m%n;            m=n;            n=t;        }        return n;    }}package c;public class Mingbs extends Maxgys{    Mingbs(int a, int b) {        super(a, b);    }    int f()    {        return a*b/super.f();    }}package shiyan2;public class Testsy2 {    public static void main(String[] args) {        Maxgys a=new Maxgys(6,9);        Mingbs b=new Mingbs(9,12);        System.out.println(a.f());        System.out.println(b.f());    }}

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