在构造函数中声明字符串数组

Question

I am trying to declare an string array in the constructor but when I run the code I get an error, however the debugger doesnt point anything out, also the code works fine when not in the constructor. It this part:

String [][] studentdetails = new String [5][3];

Error when running code with student details array in constructor is:

Exception in thread "main" java.lang.Error: Unresolved compilation problems: studentdetails cannot be resolved to a variable studentdetails cannot be resolved to a variable studentdetails cannot be resolved to a variable

at StudentMarksProgram.MarksInput(StudentMarksProgram.java:58) at StudentMarksProgram.(StudentMarksProgram.java:37) at StudentMarksProgram.main(StudentMarksProgram.java:119)

import java.util.*;


public class StudentMarksProgram {
    int studentTotal;


    double [] testaverages = new double [3];

    //In this array for student details [x][0] is the student no, [x][1] is the forename of the student, [x][2] is the surname of the student
    Scanner scanner = new Scanner(System.in);

    private int [][] marks;


    private double [] studentaverages;

    public StudentMarksProgram() {
        // TODO Auto-generated constructor stub
        System.out.println("How many students are in your class?");
        studentTotal = scanner.nextInt();
        marks = new int [studentTotal][3];
        studentaverages = new double [studentTotal];

        String [][] studentdetails = new String [studentTotal][3];
        //endless for5555 loop created to run the program and any subroutines
        for (int a=0; a<=2;) {
            int input = 0;
            System.out.println("To input marks/student details press 1,");
            System.out.println("To calculate the average press 2");
            System.out.println("To display averages press 3");
            System.out.println("To search data by student number press 4");
            input = scanner.nextInt();
            switch (input) {
            case 1:
                MarksInput();
                break;
            case 2:
                AverageCalculation();
                break;
            case 3:
                AveragePrint();
                break;
            case 4:
                searchStudentNumber();
                break;

    }
    void MarksInput () {
        for (int i=0; i<studentTotal; i++) {
            System.out.println("Enter student number of student " + (i+1) + " : ");
            studentdetails[i][0] = scanner.next();
            System.out.println("Enter the first name of student " + (i+1) + " : ");
            studentdetails[i][1] = scanner.next();
            System.out.println("Enter the surname of student " + (i+1) + " : ");
            studentdetails[i][2] = scanner.next();
            for (int j=0; j<=2;) {
                System.out.println("Enter marks for student " + (i + 1) + " in assessment " + (j +1));
                marks[i][j] = scanner.nextInt();
                if ((marks[i][j] < 41) && (marks[i][j]) >= 0) {
                    j = j +1;
                } else {
                    System.out.println("Invalid marks entered - enter a value between 0 and 40 inclusive");
                }
            }
        }

Answer 1

modify your code like this

String [][] studentdetails;
    public StudentMarksProgram() {

    studentdetails = new String [studentTotal][3];
}

As elliot mentioned the scope of studentdetails was inside your constructor. This should resolve it.

Answer 2

You shouldn't declare your array inside the constructor. Try declaring it outside and then initializing it inside the constructor