Thread: convert arraylist to 2D array

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.

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.

Originally Posted by Norm

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 !