convert arraylist to 2D array

[ishrne]

Salam ,

I'm new here , and i beleive I'll find my answer here ,
i hope you will help me.

I have data from a table in database.
this table contains ( id, name , age , class ) columns.
till now has 4 rows as well.


I created a java class called student :

 
/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package PG;
 
/**
 *
 * @author VAIO
 */
public class Student {
    String id;
    String name;
    String age;
    String clas;
 
    public Student(String id, String name, String age, String clas) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.clas = clas;
    }
 
    public String getId() {
        return id;
    }
 
    public void setId(String id) {
        this.id = id;
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public String getAge() {
        return age;
    }
 
    public void setAge(String age) {
        this.age = age;
    }
 
    public String getClas() {
        return clas;
    }
 
    public void setClas(String clas) {
        this.clas = clas;
    }
 
    @Override
    public String toString() {
        return "Student{" + "id=" + id + ", name=" + name + ", age=" + age + ", clas=" + clas + '}';
    }
 
 
 
 
 
}

------------------------------------- !

then i created Arraylist contains tables records ( but ) i inserted them student by student :
INFO: [Student{id=1, name=Ali, age=14, clas=A}, Student{id=2, name=Bdr, age=15, clas=B}, Student{id=3, name=Omar, age=13, clas=A}, Student{id=4, name=Bdr, age=12, clas=C}]

--------------------------

okey ! now i want to convert this arraylist to 2D array ,
because i want to compare first row with the rest , and then second one with the rest .. so on.

 
       Object[][] ab = new Object[a.size()][4];
            for (i = 0; i <a.size(); i++) {
               // will read the row 
                System.out.print("i value:" + i);
                // will read col 
                for (j = 0; j < 4; j++) {
                    System.out.print("i value:" + i + "," + "j value:" + j);
                    int y = 4 * i;
                //    ab[i][j] = a.get(y + j);
                    ab[i][j] = [[B] i could not complete this part[/B] ] ! 
 
                }
            }

please will you help me ,
i hope you understand my point
thanks in advance.

[Norm]

Why take the data out of the class object? Is there a problem working with an arraylist?
There are other util classes and methods that can be used with arraylists.

[ishrne]

i have no problem with using arraylist ,
but i think in this way comparing will be much easier especially I'll compare row by row.
my question is the best way of converting arraylist to 2d arrays.

[Norm]

One way would be to use a loop. What was the problem you had?

[ishrne]

One way would be to use a loop. What was the problem you had?

yes i know ,

look here

 
  Object[][] ab = new Object[a.size()][4];
            for (i = 0; i <a.size(); i++) {
               // will read the row 
                System.out.print("i value:" + i);
                // will read col 
                for (j = 0; j < 4; j++) {
                    System.out.print("i value:" + i + "," + "j value:" + j);
                    ab[i][j] = [[B] i could not complete this part[/B] ] ! 
 
                }
            }

i don't know how to fill the 2d arrays from arraylist ??
and i guess i did something wrong !

[Norm]

What data goes in the columns on a row? How can the program get that data from the objects?
The way the code is written, the class needs to have a method that takes an int value (j) and returns some data to go in the column at position j in the array.