一旦在 Java 中执行了程序，如何让 for 循环停止运行并继续执行下一个方法？

Question

该代码首先让用户输入 class 中的学生人数。然后系统将允许用户添加这些学生的姓名。 之后，用户可以为每个学生的科目分配分数和学分。 一旦为每个学生输入了分数和学分，系统就会计算 GPA。 然而，系统继续运行循环，它不执行和显示 GPA。 为什么这个循环不执行，我能得到帮助吗：

public class testing1 {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int result;
        String[] names = new String[100];
        System.out.println("Enter number of students (Must be between 1-50)");
        result = in .nextInt();
        System.out.println("Thank you, Please enter the names for the " + result + " Students");
        int nameCount = 0;
        while (nameCount < result) {
            System.out.println("Enter First Name: ");
            String s1 = in .next();
            System.out.println("The students name is" + " " + s1);
            System.out.println();
            names[nameCount] = s1;
            nameCount++;
        }
        double[][] marks = new double[100][2];
        int[][] credits = new int[100][2];
        double[] gpa = new double[100];
        String[] subjects = {"Math", "Science",};
        int cnt = 0;
        Scanner s1 = new Scanner(System.in);
        gpa[cnt] = 0;
        int totalCredits = 0;
        for (int i = 0; i < names.length; i++) {
            for(int j = 0; j < subjects.length; j++) {
                System.out.println();
                System.out.println();
                System.out.println("Please enter " + names[i] +"'s mark in "  + subjects[j] + ": ");
                marks[cnt][i] = s1.nextDouble();
                System.out.println("Please enter " + names[i] +"'s Credit hours for "+ subjects[j] + ": ");
                credits[cnt][i] = s1.nextInt();
                totalCredits += credits[cnt][i];
                gpa[cnt] += marks[cnt][i] * credits[cnt][i];
            }
            cnt++;
        }
        gpa[cnt] /= totalCredits;
        System.out.printf("GPA of :" + names[cnt] + " is %.2f.", gpa[cnt]);
        return;
    }
}

下面是我从头开始运行系统时的output：

Enter number of students (Must be between 1-50)
2
Thank you, Please enter the names for the 2 Students
Enter First Name: 
Alan
The students name is Alan

Enter First Name: 
Bob
The students name is Bob



Please enter Alan's mark in Math: 
12
Please enter Alan's Credit hours for Math: 
12


Please enter Alan's mark in Science: 
12
Please enter Alan's Credit hours for Science: 
12


Please enter Bob's mark in Math: 
12
Please enter Bob's Credit hours for Math: 
12


Please enter Bob's mark in Science: 
12
Please enter Bob's Credit hours for Science: 
12


Please enter null's mark in Math: 
12
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 2 out of bounds for length 2
    at testing1.testing1.main(testing1.java:59)

Answer 1

由于问题的更新已更改

在第一个循环中，您将遍历整个名称数组。 您还需要一个i < nameCount nameCount 条件，因为 arrays 具有从开始到与用户输入的学生一样多的数据。 因此，条件如下：

//other code
for (int i = 0; i < names.length && i < nameCount; i++) {
    //other code
}

---

如果你想停止循环，那么你可以将一些条件变量设置为 true 并根据其 state 中断循环。类似于：

for (...) {
    //sentences
    if (someCondition)
        break;
}

Answer 2

代码后的注释。

import java.util.Scanner;

public class Testing2 {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.print("Enter number of students (between 1-50): ");
        int result = in.nextInt();
        in.nextLine();
        String[] names = new String[result];
        System.out.println("Thank you, please enter the names for the " + result + " students.");
        for (int i = 0; i < result; i++) {
            System.out.printf("Enter student %d first name: ", (i + 1));
            names[i] = in.nextLine();
        }
        double[] gpa = new double[result];
        String[] subjects = {"Math", "Science",};
        double[][] marks = new double[result][subjects.length];
        int[][] credits = new int[result][subjects.length];
        for (int i = 0; i < result; i++) {
            int totalCredits = 0;
            for(int j = 0; j < subjects.length; j++) {
                System.out.printf("Please enter %s's mark in %s: ", names[i], subjects[j]);
                marks[i][j] = in.nextDouble();
                System.out.printf("Please enter %s's credit hours for %s: ", names[i], subjects[j]);
                credits[i][j] = in.nextInt();
                totalCredits += credits[i][j];
                gpa[i] += marks[i][j] * credits[i][j];
            }
            gpa[i] /= totalCredits;
            System.out.printf("GPA of %s is %.2f%n", names[i], gpa[i]);
        }
    }
}

• 您只需要一个Scanner object。无需在每次要从用户那里获取输入时都创建一个新的Scanner 。
• 在需要时声明变量。
• 您可以使用result来声明您的names数组。 然后您可以使用for循环来获取名称。
• 不需要变量s1 。 将方法nextLine返回的值直接分配给names数组。
• 您也可以在声明其他arrays时使用result ，包括marks ， credits和gpa 。 事实上，您可以使用为数组的任何维度返回int结果的任何表达式。
• 不需要变量nameCount和cnt 。
• 所有计算都需要在嵌套for循环中完成。
• 您需要为每个学生重置totalCredits 。

样本运行中的 Output：

Enter number of students (between 1-50): 2
Thank you, please enter the names for the 2 students.
Enter student 1 first name: George
Enter student 2 first name: Edson
Please enter George's mark in Math: 2.0
Please enter George's credit hours for Math: 3
Please enter George's mark in Science: 4.0
Please enter George's credit hours for Science: 2
GPA of George is 2.80
Please enter Edson's mark in Math: 2.67
Please enter Edson's credit hours for Math: 3
Please enter Edson's mark in Science: 1.33
Please enter Edson's credit hours for Science: 4
GPA of Edson is 1.90