Java [基础] 对象问题

Question

对模糊的标题表示歉意，因为我想不出这个名字是什么。

基本上创建一个计算学生财务付款的小程序。当我运行它时，它计算对象限额没有问题。然而，无论我尝试什么，对象“助学金”似乎除了 0 之外什么也没有提出。

代码如下:

import java.util.Scanner;

public class studentFinance implements Payment {
    private String stuname, department, course;
    private float budget, allowance, bursary;
    private int id, currentbudget, attendance;
    private double numbofcourses;

    // student name, id, department, course enrolledon, attendance, bursary,allowance

    //course and numbofcourses already read in
    Scanner in = new Scanner(System.in);

    public studentFinance(float currentBudget) {
        budget = currentbudget;
    }

    public float amendBudget(float newbudget) {
        budget = newbudget;//Transfer data from parameter to instance variable
        return budget;//Return statement
    }

    public float calcPayment() {
        //stuname,department,numbofcourses,attendance,id

        System.out.println("Please enter the student name");
        stuname = in.next();
        System.out.println("Please enter the department name");
        department = in.next();
        System.out.println("Please enter the number of numbofcourses");
        numbofcourses = in.nextDouble();
        System.out.println("Please enter the attendance");
        attendance = in.nextInt();
        System.out.println("Please enter their ID number");
        id = in.nextInt();
        System.out.println("Enter HND,HNC or NC");
        course = in.next();

        if (attendance > 95 & numbofcourses >= 6) {
            allowance = 1000;
        } else if (attendance > 85 & numbofcourses >5) {
            allowance = (1000 * .75F);
        } else if (attendance > 75 & numbofcourses >= 4) {
            allowance = (1000 * .5F);
        } else if (attendance > 75 & numbofcourses >= 3) {
            allowance = 100;
        } else {
            allowance = 0;
        }

        if(course=="HND") {
            bursary = 250;
        } else if(course=="HNC") {
            bursary = 200;
        } else if(course=="NC") {
            bursary = 100;
        } else {
            bursary = 0;
        }

        return bursary + allowance;
    } 

    double payment;

    public void makePayment() {
        System.out.println("The allowance total is : " + payment);
        payment = bursuary + allowance;
    }

    public void print() {

    }


}

如果有任何用途，这是用于界面的代码，还有其他元素，但我认为它们与这里无关。

interface Payment {
    public float amendBudget(float budget);
    public float calcPayment();
    public void  makePayment();
    public void  print();
}

感谢任何帮助。

Answer 1

== 并没有像你想象的那样做。 == (当应用于对象时)只是检查两个对象是否是同一个对象，而不是它们的内容是否相等，因此它不适用于此处的字符串。你想要的是:

if("HND".equals(course)) {
  // ...
} else if ("HNC".equals(course)) {
  // ...
} // etc

通常，在处理基元(int、float 等)时，您只想使用 ==，或 你明确只是想看看两个变量是否指向完全相同的对象。

您也可以将它们写为:

if(course.equals("HND")) {}

但我更喜欢在常量上使用.equals，因为你知道它们永远不会是null。这可能不是您关心的问题，但这只是我已经习惯的模式。