GPA计算器，十进制格式

Question

我有一个程序，该程序应该将您的gpa列出到最接近的小数点后两位，并且已经将其降低到最后一行，但是我收到一条错误消息，提示“无法从中引用非静态方法format（double）静态上下文”这是我的代码

import java.text.DecimalFormat;
import java.util.Scanner;

public class GPACalculator {
    public static void main(String[] args) {
        double creditHours = 0;
        double gradePoints = 0;

        System.out.println("Enter number of classes");
        Scanner scanner = new Scanner(System.in);
        double numClass = scanner.nextInt();
        DecimalFormat df = new DecimalFormat("#0.00");

        for(double i = 1; i <= numClass; i++){
            System.out.println("Enter credit hours for class "+ i);
            double aCreditHour = scanner.nextInt();
            creditHours += aCreditHour;
            System.out.println("Enter grade for class "+ i);
            String letter = scanner.next();
            if(letter.equals("A")){
                gradePoints = gradePoints + (4 * aCreditHour);
            } else if (letter.equals("B")){
                gradePoints = gradePoints + (3 * aCreditHour);
            } else if (letter.equals("C")){
                gradePoints = gradePoints + (2 * aCreditHour);
            } else if (letter.equals("D")){
                gradePoints = gradePoints + (1 * aCreditHour);
            } else if (letter.equals("F")){
                gradePoints = gradePoints + (0 * aCreditHour);
            }
        }

        System.out.println("Your GPA is: " + DecimalFormat.format(gradePoints / creditHours));
    }
}

我知道问题出在DecimalFormat之后的.format位，我只是不知道如何解决。 我只是想知道我应该用什么代替它

Answer 1

首先实例化DecimalFormat：

    DecimalFormat dFormat = new DecimalFormat();
    System.out.println("Your GPA is: " + dFormat.format(gradePoints/creditHours));

您正在直接调用非静态方法（DecimalFormat.format），这是不可能的！ 这样只能调用静态方法，另一种方法是实例化它们并通过instance.method（）调用它！