Question

我有一个关于如何将String或int或double值转换为Object Array

的问题

假设我有两节课。一个是学生班，一个是数据库班

在Student课程中，我有以下内容：

public class Student {
String name;
int grade;
double average;

}

现在在Database类中，我正在使用代码创建一些新学生：

Student studentOne = new Student();
System.out.print("Enter student 1's name: ");
studentOne.name = in.next();
Student [] students = new Student [5];

现在，如果我创建：

students[0] = studentOne.name; // It gives me the following error: "Type mismatch: cannot convert from String to Student"

现在我明白我无法将字符串转换为对象，但在谷歌或此处搜索之后，我找不到如何完成此操作的方法。你能“投”到一个物体里吗？或.toObject方法？我很困惑。

谢谢和最好的问候

Answer 1

您的数组属于Student类型且studentOne.name属于String类型，您无法为String类型数组指定Student类型值。只能在Student数组中添加student类型对象。

students[0] = studentOne.name;无效。

将其更改为

students[0] = studentOne;

此外，您首先需要实例化每个Student对象，然后才能对其执行任何操作。

在students[0] = new Student();

之前添加students[0] = studentOne;

Answer 2

您可以采取以下措施让不同数量的学生添加

public class Main {

    public static class Student {
        String name;
        int grade;
        double average;

        public Student()
        {
            name = "Nothing";
            grade = -1;
            average = 0.0;
        }

        public void PrintStudent()
        {
            System.out.println("[" + name + ", " + grade + ", " + average + "]");
        }

    }

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);
        Student [] students = null;
        System.out.print("Enter How Many Students to Create: ");
        String numberOfStudents = in.nextLine();

        if(numberOfStudents.matches("\\d+"))
        {
            students = new Student [Integer.parseInt(numberOfStudents)];
        }
        else 
        {
            System.err.println("Error when reading user input, exiting...");
            return;
        }

        CreateStudents(students, in);
        PrintStudents(students);


    }//main method

    public static void CreateStudents(Student[] allStudents, Scanner inputOrigin)
    {
        System.out.println("Enter Students as CSV(Comma Seperated Values).\nExample Given: Pete The Dragon, 11, 3.67");
        for(int studentIndex = 0; studentIndex < allStudents.length; studentIndex++)
        {
            System.out.println("Enter information for student #" + studentIndex + ": ");
            String[] input = inputOrigin.nextLine().split(",");
            try{
                //note how each index is a value of the student object in the input string array
                Student newStudent = new Student();
                newStudent.name = input[0];
                newStudent.grade = Integer.parseInt(input[1].replaceAll(" ", ""));
                newStudent.average = Double.parseDouble(input[2].replaceAll(" ", ""));
                allStudents[studentIndex] = newStudent;
            }
            catch(Exception ex)
            {
                System.err.println("Failed to create the " + studentIndex + " due to the following:" + ex.toString());
                allStudents[studentIndex] = new Student();
                    //or we can terminate 
                //return;
            }
        }
    }

    public static void PrintStudents(Student[] allStudents)
    {
        System.out.println("The students are as follows:");
        for(int index = 0; index < allStudents.length; index++)
        {
            System.out.print(index + ": ");
            if(allStudents[index] != null)
                allStudents[index].PrintStudent();
        }
    }
}

以下是我们添加5名学生的程序的单次运行的以下输出。需要注意的是，当我在尝试创建学生时遇到异常时，我将添加一个默认的Student对象。如果你想，你可以停止添加学生，只需退出。然而，如果用户搞砸了，能够继续创建学生真是太好了。

输出

Enter How Many Students to Create: 5
Enter Students as CSV(Comma Seperated Values).
Example Given: Pete The Dragon, 11, 3.67
Enter information for student #0: 
ryan, 4, 3.33
Enter information for student #1: 
harambe the great, 12, 4.32
Enter information for student #2: 
some other person, 6, 2.45
Enter information for student #3: 
donald trump, 1, 0.35
Enter information for student #4: 
another person, incorrect vlaue example, 4.67
The students are as follows:Failed to create the 4 due to the following:java.lang.NumberFormatException: For input string: "incorrectvlaueexample"

0: [ryan, 4, 3.33]
1: [harambe the great, 12, 4.32]
2: [some other person, 6, 2.45]
3: [donald trump, 1, 0.35]
4: [Nothing, -1, 0.0]

Answer 3

您有一组Student个对象。因此，您只能将Student实例分配给其中一个阵列插槽。 Student.name是String。对我来说，这似乎是合乎逻辑的，你的意图是将整个Student对象分配给你的数组，而不仅仅是名字。只需更改：

students[0] = studentOne.name;

到

students[0] = studentOne;

这将纠正您的类型不匹配错误。

将字符串/整数转换为对象数组

3 个答案: