如何将数据添加到二维数组？

Question

I have to create a program that uses a two-dimensional array to store student names and their grades. The user inputs the students name and their grades and it is then supposed to be added. It has to be able to hold data for 15 students. Can someone tell me how to add data to such an array? I have attached my code so far, as well as my design preview.

public class StudentGrades extends javax.swing.JFrame {
    double [][] database = new double[4][15];
/**
 * Creates new form StudentGrades
 */
public StudentGrades() {
    initComponents();
    displayButton.setEnabled(false);
    studentButton.setEnabled(false);
    courseButton.setEnabled(false);
}

...

private void exitButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           
    //set code to close program
    System.exit(0);
}                                          

private void addButtonActionPerformed(java.awt.event.ActionEvent evt) {                                          
    //clear output area
    outputArea.setText(null);

    //enable buttons
    displayButton.setEnabled(true);
    studentButton.setEnabled(true);
    courseButton.setEnabled(true);

    //declare variables
    double grade1 = Double.parseDouble(test1.getText());
    double grade2 = Double.parseDouble(test2.getText());
    double grade3 = Double.parseDouble(test3.getText());
    double grade4 = Double.parseDouble(test4.getText());

User Interface

Answer 1

Any addition of data into a two-dimensional array is based on the row and the column:

means for 2d-array with size of NXN:

database[0];       // Related to the first row in the array
database[0][0];    // Is the top left cell in the array.
database[N-1]      // Related to the last array row
database[N-1][N-1] // Is the down right cell in the array.

If you wish to add grade3 into the array for the second student you should insert the grade into:

 database[1][2]

Why? Because the counting in the array is zero based, and hence the second student data is saved in

database[1]  // The second array row.

The first grade should be save in column number 0:

database[1][0]

The second grade should be save in column number 1:

database[1][1]

The third grade should be save in column number 2:

database[1][2]

Here you have a very useful link related to grades 2d-arrays .

Tip for best practice:

When using two-dimensional array it is a good practice to make the numbers in the array as static final names with meaning. Instead of:

double [][] database = new double[4][15];

For example you can try the following syntax:

private static final Integer NUM_OF_STUDENTS = 4
private static final Integer NUM_OF_TESTS = 15
double [][] database = new double[NUM_OF_STUDENTS][NUM_OF_TESTS];

Answer 2

This is what a 2d array looks like:

So, according to my understanding, this is how you should declare your 2d array:

double [][] database = new double[15][5];

It means that there are 15 rows (15 students) and 5 columns (1 column to store the name and the other 4 to store the grades of that student). Now you need a way to store both name and grade in the same array. So the only you can do this is if you declare the type of the array an Object .

Object [][] database = new Object[15][5];

An Object can hold any type of data. Here is an example:

database[0][0] = "jon skeet";
database[0][1] = 4.0; // grade in double type... you can also keep it as String
database[0][2] = 4.0;
database[0][3] = 4.0;
database[0][4] = 4.0;

If 2d array is not a requirement then I would suggest you to use a HashMap or something else.

Answer 3

Create a Class Student in that class put an Array of Notes, then in the StudenGrade class create an array of Students

class Student {
 int []grades;
 String name;

 public Student(String name, int NGrades){
 this.name = name
 grades = new int[NGrades];
 }
 public void setGrade(int index, int grade){
 grade[index] = grade;
 }
 public int getGrade(int index){
 return grade[index];
 }
 public String getName(){
 return name;
 }
}

class StudentGrades {
 Student students[];

 public StudentGrades(int NStudents, int NGrades){
 students = new Student[NStudents];
 String names[] = {"Bob","Pete","Rafi","Roff"};
 for(int i=0;i<NStudents;i++){
  students[i] = new Studen(names[i],NGrades);
 }
}