用Java创建类时遇到麻烦。 不确定某些方法

Question

ok so this is the assignment that I'm working on:

"Implement a class Student (you may use the one you created for lab and add on to it). In addition to any other attributes that the class already has, the student object will have a total quiz score. Be sure to write a complete class (ie proper attributes, constructor, accessors and mutators).

Other methods needed are: addQuiz(int score), showStudentInfo(), and getAverageScore(). Note that in order to calculate average, the class needs to know the number of quizzes. The driver/tester class will create three (3) student objects. Each student object's method will be called five times to add five (5) quiz grades.

I recommend that you use Random class to generate the quiz values, instead of hard-coding them.Then the driver calls Student's method to display the students' name, all five quiz grades, and the average score of the quizzes."

I have a basic idea of what needs to be done but I'm just unsure on some of the methods. For example the "getAverageScore" method is the one that I'm having trouble with. Also do I even need the get and set methods for age name and major if I'm am just initializing them at the beginning of the tester program? Any help on what needs to be added or fixed with my class is greatly appreciated. Here is the code that I have so far:

import java.util.Random;

public class Student
{
  private int Age;
  private String Name;
  private String Major;
  private int Score;

  public Student(String n, int a, String m)
  {
    Name = n;
    Age = a;
    Major = m;
  }

  public String showStudentinfo()
  { return (Name + " " + Age + " " + Major + "\n");
  }

  public int addQuiz()
  { Score = randomNumbers.nextInt(101);
    return Score;
  }

  public int getAverageScore()
  { 
  }

  //setter methods
  public void setAge(int a)
  { Age = a;
  }
  public void setName(String n)
  { Name = n;
  }
  public void setMajor(String m)
  { Major = m;
  }

  //getter methods
  public int getAge()
  { return Age;
  }
  public String getName()
  { return Name;
  }
  public String getMajor()
  { return Major;
  }
}

Answer 1

Most of it looks fine, but there are a couple issues, mostly style-related (maybe a bit subjective).

1) You don't initialize randomNumbers anywhere.

2) Variable names should start with lower case letters. Capitalized names are generally reserved for classes.

3) Don't use single letter variable names, even for arguments. They're annoying and obscure information. Use something more informative like setAge(int newAge).

4) It sounds like they want you to store the sum of all test scores (which is weird, but hey) and then calculate the average. To get the average from a sum you're going to need to know how many tests are included in the sum, so you'll have to keep track of that somewhere and increment it accordingly. In addQuiz right now you're just keeping track of the score of the most recent quiz.

5) Don't start the body of a function on the same line as the {, it's ugly.

Answer 2

In order for getAverageScore() to work, you'll need to keep track of individual scores. You could do something like use an ArrayList<Integer> and add individual scores to them. (Alternatively, you could keep an avgScore attribute, along with a numOfTests attribute, and compute the new average from that---though if you want the average as an int this could become more inaccurate over time).

Here is part of a solution that relies on ArrayList<Integer> . I assume here your method signature is correct, and you don't actually want to return a double or float (ie you're going to have to round up/down the score).

public int getAverageScore() {
    float sum = 0.0; // so rounding works, integer division truncates
    // in case you're not familiar with it,
    // read the following line as "for each score in scoreList"
    for (Integer score : scoreList) { // scoreList is of type ArrayList<Integer>
       sum = sum + score;
    }
    return Math.round(sum / scoreList.size());
}

Now, I don't show you how to properly implement scoreList , as this is homework and you should still do some of it yourself. A hint: You can't use primitive types (like int ) in an ArrayList , you'll need to instead store Integer s. You can create an integer of a particular value with new Integer(int value) . If, instead, you knew there were going to be a fixed number of scores, you could use an int array.

For this solution to work, you'll need to add the scoreList attribute, and you'll need to change how addQuiz() works.

Answer 3

fields should start with a lower case. Setters are not mandatory, it just depends if it makes sense or not. Methos addQuiz should take an int as an argument and you should have a field int numberOfQuizzes. That field should be incremented everytime a quiz score is added. The average score is then just the total of the scores divided by the number of quizzes

Answer 4

You must keep sum of all scores and number of quizes taken, so add 2 fields, sumOfQuizGrades and countOfQuizGrades , and by method addQuiz add the grade to sum and increment the count.

By the way don't change the signature of the addQuiz it must not hold the random within it, the random shall be added in main method.

Answer 5

You need to store the quiz grades somewhere. Your professor said there would be more than one. Above the 'Student' constructor, add either an Array of size 5 or an ArrayList. I will use an Array for this, so:

private int[] scores = new int[5];

Then in your method that gets the scores, add them to the Array with a Loop:

public void addQuiz() { 
    for(int i = 0; i < 5; i++){ //Loops through and adds 5 scores
    int score = randomNumbers.nextInt(101);
    scores[i] = score;
    }
}

Then you should be able to calculate the average of the scores by adding the grades together and dividing them by 5:

public int getAverageScore() {
    int totalScore = scores[0] + scores[1] + scores[2] + scores[3] + scores[4];
    int avgScore = totalScore / 5;
    return avgScore;
}

I have not actually tested this code, and I am a beginner myself, but hopefully this puts you on the right track. :)