要求：根据不同学生的等级进行不同的分数成绩评定

1、封装

1、封装的概念

。。。

package bao;

abstract class Student {
    

	final static int CourseNo = 3;// 课程
	String name;// 姓名
	String type; // 类型
	int[] courses;// 成绩的数组
	String courseGrade;// 等级

	public Student(String name) {
    
		this.name = name;
		courses = new int[CourseNo];
		courseGrade = " ";// 初始成绩等级为空字符
	}

	public abstract void calculateGrade();// 计算总成绩的抽象方法

	public String getName() {
    
		return name;
	}

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

	public String getType() {
    
		return type;
	}

	public void setType(String type) {
    
		this.type = type;
	}

	public void setCourseScore(int courseNumber, int courseScore) {
    
		courses[courseNumber] = courseScore; // 按课程索引号设置课程的成绩
	}

	public int getCourseScore(int courseNumber) {
    
		return courses[courseNumber];
	}

	public void setCourseGrade(String courseGrade) {
    
		this.courseGrade = courseGrade;
	}

	public String getCourseGrade() {
    
		return courseGrade;
	}

}

2、继承

接口：。。。
抽象类：。。。

2.1、本科生继承学生类

package bao;

class Undergraduate extends Student {
    

	public Undergraduate(String name) {
     // 构造方法
		super(name); // 使用super调用父类的构造方法
		type = "本科生"; // 初始化父类的属性

	}

	@Override
	public void calculateGrade() {
     // 实现父类的抽象方法

		int total = 0;
		double average = 0;
		for (int i = 0; i < CourseNo; i++) {
     // 所有课程的成绩总和
			total += courses[i];
		}
		average = total / CourseNo; // 计算平均成绩
		if (average >= 90 && average < 100)
			courseGrade = "优秀";
		else if (average >= 80 && average < 90)
			courseGrade = "良好";
		else if (average >= 70 && average < 80)
			courseGrade = "一般";
		else if (average >= 60 && average < 70)
			courseGrade = "及格";
		else
			courseGrade = "不及格";

	}

}

2.2、 研究生继承学生类

package bao;

class Postgraduate extends Student {
    

    public Postgraduate(String name) {
    
        super(name);
        type = "研究生";
    }

    public void calculateGrade() {
     // 实现父类的抽象方法

        int total = 0;
        double average = 0;
        for (int i = 0; i < CourseNo; i++) {
     // 所有课程的成绩总和
            total += courses[i];
        }
        average = total / CourseNo; // 计算平均成绩
        if (average >= 95 && average < 100)
            courseGrade = "优秀";
        else if (average >= 85 && average < 95)
            courseGrade = "良好";
        else if (average >= 75 && average < 85)
            courseGrade = "一般";
        else if (average >= 65 && average < 75)
            courseGrade = "及格";
        else
            courseGrade = "不及格";

    }

}

3、多态

多态的概念：。。。

package bao;

public class Polymorphism {
    

	public static void main(String[] args) {
    
		// TODO Auto-generated method stub
		Student[] students = new Student[5];
		// 父类引用子类的对象
		students[0] = new Undergraduate("张三");
		students[1] = new Undergraduate("赵薇");
		students[2] = new Postgraduate("李四");
		students[3] = new Undergraduate("杨密");
		students[4] = new Postgraduate("唐洋");
		for (int i = 0; i < 5; i++) {
    
			students[i].setCourseScore(0, 88);
			students[i].setCourseScore(1, 90);
			students[i].setCourseScore(2, 96);
		}
		for (int i = 0; i < 5; i++) {
    
			students[i].calculateGrade();// 调用各自类中的方法
		}
		System.out.println("姓名 " + " 类型" + " 成绩");
		System.out.println("--------------------------------------------");
		for (int i = 0; i < 5; i++) {
    
			System.out
					.println(students[i].getName() + " " + students[i].getType() + " " + students[i].getCourseGrade());
		}

	}

}

4、测试结果