Question

我刚刚了解了构造函数，并且必须在最近的程序中使用它们。我做对了，但我仍然不明白他们做了什么。如果有人可以使用这个程序给我一个详细的解释作为参考，这将是伟大的！

MAIN CLASS

public class Student 
{

public static void main(String[]args)
{

    String question, name, GPAStr, studentNumberStr;
    int studentNumber;
    double GPA;

    question = JOptionPane.showInputDialog("Would you like to see if you Qualify for the Dean's List? (Y or N)");

    while (question.equalsIgnoreCase("Y"))
    {
        name = JOptionPane.showInputDialog("Please enter your name.");

        studentNumberStr = JOptionPane.showInputDialog("Please enter your student number.");
        studentNumber = Integer.parseInt(studentNumberStr);

        GPAStr = JOptionPane.showInputDialog("Please enter your GPA.");
        GPA = Double.parseDouble(GPAStr);

        StudentIO students = new StudentIO(name, GPA);

        // ouput

        JOptionPane.showMessageDialog(null, students.getDeansList());

        question = JOptionPane.showInputDialog("Would you like to see if you Qualify for the Dean's List? (Y or N)");

        if (question.equalsIgnoreCase("N"))
            //display the content of players processed

        {
            JOptionPane.showMessageDialog(null,StudentIO.getCount());
        }
    }
}
}

第二类（其中包含建筑师的标签）

public class StudentIO 
{

//instance fields

    private String name;
    private double GPA;

    // static fields

    private static final double GPAMIN=3.0;
    private static int count = 0;

    public StudentIO(String theName, double theGPA)  // constructor
    {
        name = theName;
        GPA= theGPA;

        count = count +1;
    }

    public StudentIO()    //no arg constructor
    {
        name = " ";
        GPA = 0;

        count = count +1;
    }

    public void setName(String theName)
    {
        name = theName;
    }

    public void setGPA(double theGPA)
    {
        GPA = theGPA;
    }


    public String getName()
    {
        return name;
    }

    public double getGPA()
    {
        return GPA;
    }

    public String getDeansList()
    {
        if(GPA >= GPAMIN)
            return (name + ", has made the Dean's List!");
        else
            return(name + ", did not make the Dean's List!");

    }

    public static String getCount()
    {
        return ("You processed " + count + "students.");
    }
}

Answer 1

StudentIO students = new StudentIO(name, GPA);

将创建一个名为students的StudentIO对象，并影响使用第一个承包商创建的对象的名称和GPA参数：

 public StudentIO(String theName, double theGPA)  // constructor
    {
        name = theName;
        GPA= theGPA;

        count = count +1;
    }

这相当于召唤：

StudentIO students = new StudentIO();
students.setName(name);
students.setGPA(GPA);

将使用seconde承包商：

public StudentIO()    //no arg constructor
{
    name = " ";
    GPA = 0;

    count = count +1;
}

使用两种方法

public void setName(String theName)
{
    name = theName;
}

public void setGPA(double theGPA)
{
    GPA = theGPA;
}

最后，这两种方法给你的结果相同，它的风格很重要，有时我们被迫在强耦合对象中使用秒数。

Answer 2

count = count +1;

看来你在构造函数中指的是这一行。变量count是StudentIO类中的静态成员，用于跟踪使用参数化或默认构造函数创建的StudentIO对象的数量。

Answer 3

StudentIO类的构造实例。它们的目的是为StudentIO的新实例设置初始状态。每个实例都有自己的状态。静态变量在实例之间共享，因此在每个构造中，您将向计数中添加一个。它会告诉你已经创建了多少个实例（我猜）。

向我解释一下这些构造函数在这个程序中做了什么？

3 个答案: