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Thread: convert arraylist to 2D array

  1. #1
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    Default 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.


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: convert arraylist to 2D array

    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.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: convert arraylist to 2D array

    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.

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: convert arraylist to 2D array

    One way would be to use a loop. What was the problem you had?
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
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    Default Re: convert arraylist to 2D array

    Quote Originally Posted by Norm View Post
    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 !

  6. #6
    Super Moderator Norm's Avatar
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    Default Re: convert arraylist to 2D array

    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.
    If you don't understand my answer, don't ignore it, ask a question.

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