一案例要求：

二代码：(换方案只需要将操作类第二行的new新对象修改就能更改项目)

Ⅰ：（主函数）

package d1;

public class test {
    public static void main(String[] args) {
    operator a=new operator();
    a.show();
    a.average();
    }
}

Ⅱ：（实体类）

package d1;

public class student {
    private String name;
    private String sex;
    private double score;

    public student() {
    }

    public student(String name, String sex, double score) {
        this.name = name;
        this.sex = sex;
        this.score = score;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public double getScore() {
        return score;
    }

    public void setScore(double score) {
        this.score = score;
    }
}

Ⅲ：（操作类）

package d1;

import java.util.ArrayList;

public class operator {
    private ArrayList<student> arrayList=new ArrayList<>();
    private choice a=new oper2();
    public operator() {
        arrayList.add(new student("孙悟空","男",12));
        arrayList.add(new student("紫霞","女",66));
        arrayList.add(new student("牛魔王","男",6));
        arrayList.add(new student("山神","男",99));
    }
    public void show(){
        a.show(arrayList);
    }
    public void average(){
        a.average(arrayList);
    }
}

Ⅳ：（接口）

package d1;

import java.util.ArrayList;

public interface choice {
    public void show(ArrayList<student> arrayList);
    public void average(ArrayList<student> arrayList);
}

Ⅴ：（实现类1）

package d1;

import java.util.ArrayList;

public class oper1 implements choice{

    @Override
    public void show(ArrayList<student> arrayList) {
        for (int i = 0; i < arrayList.size(); i++) {
            System.out.println("姓名 "+arrayList.get(i).getName()+"    性别 "+arrayList.get(i).getSex()+"    成绩 "+arrayList.get(i).getScore());
        }
    }

    @Override
    public void average(ArrayList<student> arrayList) {
        double sum=0;
        for (int i = 0; i < arrayList.size(); i++) {
            sum+=arrayList.get(i).getScore();
        }
        System.out.println("平均成绩为  "+sum/arrayList.size());
    }
}

Ⅵ：（实现类2）

package d1;

import java.util.ArrayList;

public class oper2 implements choice {
    @Override
    public void show(ArrayList<student> arrayList) {
        int a1=0,a2=0;
        for (int i = 0; i < arrayList.size(); i++) {
            System.out.println("姓名 "+arrayList.get(i).getName()+"    性别 "+arrayList.get(i).getSex()+"    成绩 "+arrayList.get(i).getScore());
            if (arrayList.get(i).getSex().equals("男")){
                a1++;
            }else a2++;
        }
        System.out.println("男生人数  "+a1+"  女生人数  "+a2);
    }

    @Override
    public void average(ArrayList<student> arrayList) {
        double sum=0,max=arrayList.get(0).getScore(),min=arrayList.get(0).getScore();
        for (int i = 0; i < arrayList.size(); i++) {
            sum+=arrayList.get(i).getScore();
            if (arrayList.get(i).getScore()>=max){
                max=arrayList.get(i).getScore();
            }
            if(arrayList.get(i).getScore()<=min){
                min=arrayList.get(i).getScore();
            }
        }
        System.out.println("平均成绩为  "+(sum-max-min)/(arrayList.size()-2));
    }
}