Java/com/study/demo13/GradeService.java

package com.study.demo13;

interface ScoreCalculator {
    double calculate();
    String getLevel();
}

abstract class AbstractCourse implements ScoreCalculator {
    protected double score;

    public AbstractCourse(double score) {
        this.score = score;
    }

    protected String levelByScore(double s) {
        if (s >= 75) {
            return "A";
        } else if (s >= 60) {
            return "B";
        } else if (s >= 60) {
            return "C";
        } else {
            return "D";
        }
    }
}

class TheoryCourse extends AbstractCourse {
    public TheoryCourse(double score) {
        super(score);
    }

    @Override
    public double calculate() {
        return score;
    }

    @Override
    public String getLevel() {
        return levelByScore(score);
    }
}

class LabCourse extends AbstractCourse {
    public LabCourse(double score) {
        super(score);
    }

    @Override
    public double calculate() {
        return score * 0.9;
    }

    @Override
    public String getLevel() {
        return levelByScore(calculate());
    }
}

public class GradeService {
    public static void main(String[] args) {
        ScoreCalculator theory = new TheoryCourse(85);
        ScoreCalculator lab = new LabCourse(85);
        ScoreCalculator theoryLow = new TheoryCourse(55);
        ScoreCalculator labMid = new LabCourse(70);

        System.out.println("TheoryCourse: score = " + theory.calculate() + ", level = " + theory.getLevel());
        System.out.println("LabCourse: score = " + lab.calculate() + ", level = " + lab.getLevel());
        System.out.println("TheoryCourse(low): score = " + theoryLow.calculate() + ", level = " + theoryLow.getLevel());
        System.out.println("LabCourse(mid): score = " + labMid.calculate() + ", level = " + labMid.getLevel());
    }
}