Extending an multidimensional array (2D) in Java

How can I extend a multidimensional array in Java?

I need to extend its first dimension. It's in a format like:

myArray[x][7]

The "开发者_Python百科;7" will stay "7" on all extended parts.

Arrays in Java have fixed length, so you can't really extend it. You will have to create a new, larger, array, and then copy the content of the old array into the new one. Like this:

public class Test {

    public static void main(String[] args) {
        int[][] myArray = new int[3][7];

        // Print first dimension
        System.out.println(myArray.length);   // prints 3

        myArray = addRow(myArray);

        // Print first dimension
        System.out.println(myArray.length);   // prints 4

    }

    private static int[][] addRow(int[][] previous) {

        int prevRowCount = previous.length;

        int[][] withExtraRow = new int[prevRowCount + 1][];
        System.arraycopy(previous, 0, withExtraRow, 0, previous.length);
        withExtraRow[prevRowCount] = new int[] { 1, 2, 3, 4, 5, 6, 7 };

        return withExtraRow;
    }

}

You could of course also use for instance an ArrayList<SomeType[]> that grows dynamically. (This is actually the preferred way when dealing with dynamically growing arrays.)

import java.util.*;

public class Test {

    public static void main(String[] args) {
        List<int[]> myArray = new ArrayList<int[]>();

        // Print first dimension
        System.out.println(myArray.size());   // prints 0

        // Add three rows
        myArray.add(new int[] {  1,  2,  3,  4,  5,  6,  7 });
        myArray.add(new int[] { 11, 12, 13, 14, 15, 16, 17 });
        myArray.add(new int[] { 21, 22, 23, 24, 25, 26, 27 });

        // Print first dimension
        System.out.println(myArray.size());   // prints 3

    }
}

You could also use Arrays.copyOf method, for example:

import java.util.Arrays;

public class Array2D {
    public static void main(String[] args) {
        int x = 5 //For example
        int[][] myArray = [x][7];

        myArray = Arrays.copyOf(myArray, myArray.length + 1); //Extending for one
        myArray[myArray.length - 1] = new int[]{1, 2, 3, 4, 5, 6, 7};
    }
}

if you want to do this, make a class that contains the array as an instance variable and handles all interaction with it.

You can't.

You could create a new array with the correct dimensions, but I would recommend reading up about the ArrayList class which (as far as you need to know) allows for dynamic arrays.