2D数组数据为空

Question

我创建了一个程序来接受来自用户的输入，并将存储在2d数组中。示例情况下，用户输入的输入号为学期= 2;那么no当然也= 2;我的循环工作正常，但是数据不能很好地存储。

输出:零零零input4

应该是这样的:input1input2input3input4

下面是我的代码:

BufferedReader inData = new BufferedReader(new InputStreamReader(System.in));
    try {
        System.out.print("Enter no of semester : ");
        data = inData.readLine();
        noSem = Integer.parseInt(data);
        // Semester loop
        for(int i = 0; i < noSem; i++) {
            System.out.println("ntSemester" + (i + 1));
            System.out.print("Enter number of course : ");
            data = inData.readLine();
            noCourse = Integer.parseInt(data);
            // course details loop
            for(int u = 0; u < noCourse; u++) {
                System.out.println("Enter Course Code : ");
                System.out.print("Enter Course Name : ");
                sbjName = new String[noSem][noCourse];
                sbjName[i][u] = inData.readLine();
                System.out.println("Enter Credit Hour : ");
                System.out.println("Enter Marks : ");
                System.out.println("n");
            }
        }
        for(int x = 0; x < noSem; x++) {
            for(int y = 0; y < noCourse; y++) {
                System.out.println(sbjName[x][y]);
            }
        }
    }

Answer 1

BufferedReader inData = new BufferedReader(new InputStreamReader(System.in));
try {
    System.out.print("Enter no of semester : ");
    int noSem = Integer.parseInt(inData.readLine());
    String[][] sbjName = new String[noSem][];
    // Semester loop
    for (int i = 0; i < noSem; i++) {
        System.out.println("ntSemester" + (i + 1));
        System.out.print("Enter number of course : ");
        int noCourse = Integer.parseInt(inData.readLine());
        sbjName[i] = new String[noCourse];
        // course details loop
        for (int u = 0; u < noCourse; u++) {
            System.out.println("Enter Course Code : ");
            System.out.print("Enter Course Name : ");
            sbjName[i][u] = inData.readLine();
            System.out.println("Enter Credit Hour : ");
            System.out.println("Enter Marks : ");
            System.out.println("n");
        }
    }
    for (int x = 0; x < sbjName.length; x++) {
        for (int y = 0; y < sbjName[x].length; y++) {
            System.out.println(sbjName[x][y]);
        }
    }
}

Answer 2

你的问题在这里:

sbjName = new String[noSem][noCourse];

语句在每次迭代期间创建一个新数组。换句话说:你丢掉了之前创建的数组;因此，之前存储在这些数组中的任何信息…也被扔掉了!

你只希望调用一次;所以你把移到循环的之外!

Answer 3

问题似乎是每次执行第一个for循环时都要重新创建2d数组。

要解决这个问题，您需要在开始时定义可用的课程数量:

    BufferedReader inData = new BufferedReader(new InputStreamReader(System.in));
    String[][] sbjName = null;
    String data;
    int noSem = 2;
    int noCourse = 3; // say there are 3 courses that are available
    try {
        System.out.print("Enter no of semester : ");
        data = inData.readLine();
        noSem = Integer.parseInt(data);
        System.out.print("Enter number of courses available : ");
        data = inData.readLine();
        noCourse = Integer.parseInt(data);
        sbjName = new String[noSem][noCourse];
        // Semester loop
        for (int i = 0; i < noSem; i++) {
            System.out.println("ntSemester" + (i + 1));
            System.out.print("Enter number of course : ");
            data = inData.readLine();
            int courseNum = Integer.parseInt(data);
            // course details loop
            for (int u = 0; u < courseNum; u++) {
                System.out.println("Enter Course Code : ");
                System.out.print("Enter Course Name : ");
                sbjName[i][u] = inData.readLine();
                System.out.println("Enter Credit Hour : ");
                System.out.println("Enter Marks : ");
                System.out.println("n");
            }
        }
        for (int x = 0; x < noSem; x++) {
            for (int y = 0; y < noCourse; y++) {
                System.out.println(sbjName[x][y]);
            }
        }
    } catch (Exception e) {
    }