一旦在 Java 中執行了程序，如何讓 for 循環停止運行並繼續執行下一個方法？

Question

該代碼首先讓用戶輸入 class 中的學生人數。然后系統將允許用戶添加這些學生的姓名。 之后，用戶可以為每個學生的科目分配分數和學分。 一旦為每個學生輸入了分數和學分，系統就會計算 GPA。 然而，系統繼續運行循環，它不執行和顯示 GPA。 為什么這個循環不執行，我能得到幫助嗎：

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;
    }
}

下面是我從頭開始運行系統時的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

由於問題的更新已更改

在第一個循環中，您將遍歷整個名稱數組。 您還需要一個i < nameCount nameCount 條件，因為 arrays 具有從開始到與用戶輸入的學生一樣多的數據。 因此，條件如下：

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

---

如果你想停止循環，那么你可以將一些條件變量設置為 true 並根據其 state 中斷循環。類似於：

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

Answer 2

代碼后的注釋。

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]);
        }
    }
}

• 您只需要一個Scanner object。無需在每次要從用戶那里獲取輸入時都創建一個新的Scanner 。
• 在需要時聲明變量。
• 您可以使用result來聲明您的names數組。 然后您可以使用for循環來獲取名稱。
• 不需要變量s1 。 將方法nextLine返回的值直接分配給names數組。
• 您也可以在聲明其他arrays時使用result ，包括marks ， credits和gpa 。 事實上，您可以使用為數組的任何維度返回int結果的任何表達式。
• 不需要變量nameCount和cnt 。
• 所有計算都需要在嵌套for循環中完成。
• 您需要為每個學生重置totalCredits 。

樣本運行中的 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