将对象存储在数组数组中

Question

I have got a question regarding an assignment I need to finish. Basically I need to store coordinates in their respective objects and store them in an array. There are multiple sets of coordinates which all need a separate array, all these arrays again need to be stored in an array.

This is a simple version of what I'm trying to do, using 3 classes:

package test2;

import java.io.PrintStream;
//import java.util.Scanner;


public class Test {

PrintStream out;

Test(){
    out = new PrintStream(System.out);
}

    Coordinate[] row = new Coordinate[5];
    CoordinateRow[] main = new CoordinateRow[10];

    void start(){


    row[0] = new Coordinate(4, 9);
    row[1] = new Coordinate(4, 1);
    row[2] = new Coordinate(0, 4);

    main[0] = new CoordinateRow(row);


    row[0] = new Coordinate(5, 3);
    row[1] = new Coordinate(7, 2);
    row[2] = new Coordinate(4, 8);


    main[1] = new CoordinateRow(row);

    out.println(main[0].row[0].y);




    }

    public static void main(String[] args) {
    // TODO Auto-generated method stub
    new Test().start();
}

}




package test2;


public class Coordinate{

    int x;
    int y;

    Coordinate(int x, int y){

        this.x = x;
        this.y = y;     

    }

}

package test2;

import test2.Coordinate;


public class CoordinateRow {

    Coordinate[] row;

    CoordinateRow(Coordinate[] row){
        this.row = row;

    }
}

When i vary the values in the arrays in the print statement it always displays the last set of coordinates inserted.

I hope someone can explain what I'm doing wrong.

Answer 1

You are using the same array row , this won't work because of passing reference instead of values. You should create new array. Both main[0] and main[1] contains the same reference

SubClass[] row = new SubClass[5];
SubClass[] row2 = new SubClass[5];
SubClass2[] main = new SubClass2[10];

void start(){


row[0] = new SubClass(4, 9);
row[1] = new SubClass(4, 1);
row[2] = new SubClass(0, 4);

main[0] = new SubClass2(row);


row2[0] = new SubClass(5, 3);
row2[1] = new SubClass(7, 2);
row2[2] = new SubClass(4, 8);


main[1] = new SubClass2(row2);

out.println(main[0].row[0].y);

}

this is only a part of code...