初始化二维数组（java）

Question

I am trying to initialise an 2-d array with some objects. And I want the 2nd "dimension" to have arrays of different sizes eg different powers of to. And my idea is the following code:

NodeMatrix=new BNode[n][];
    for(int i=0;i<n;i++) {
        for(int j=0;j<Math.pow(2,i);j++) {
            NodeMatrix[i]=new BNode[(int)Math.pow(2,i)];
            NodeMatrix[i][j]= new BNode(i);
        }

but it doesnt work and I have now other idea how it could be done.

Answer 1

I didn't understood your requirement completely. But the below code may help you to understand the 2D arrays in Java.

public static void generateDynamicArray() {
        int[][] arr = new int[5][];

        for (int i = 0; i < arr.length; i++) {
            arr[i] = new int[(int)Math.pow(2, i)];
        }


        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                arr[i][j] = (int) (Math.random() * 10);
            }
        }


        for(int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[i].length; j++) {
                System.out.print(arr[i][j] +" ");
            }
            System.out.println();
        }
    }

Answer 2

You have to initialize BNode array before you iterate over it. As an advice, consider if you really want to set length by powers of two, that will grow fast.

NodeMatrix=new BNode[n][];
for(int i=0;i<n;i++) {
    NodeMatrix[i]=new BNode[(int)Math.pow(2,i)];
    for(int j=0; j < NodeMatrix[i].length; j++) {  
        NodeMatrix[i][j]= new BNode(i);
    }
}

Answer 3

Basically, It cannot be done in java. 2 d array is nothing but just array of arrays.

One option can be use a list of arrays.

Example:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class JavaArrayListOfStringArray {

    public static void main(String[] args) {

        List <String[]> list = new ArrayList <String[]>();

        String [] arr1 = {"a","b","c"};
        String [] arr2 = {"1","2","3"};

        list.add(arr1);
        list.add(arr2);

        for(String[] arr : list) {
            System.out.println(Arrays.toString(arr));
        }
    }

}