How to put an array(s) into another array - Java

Question

I am trying to put an array(s) into another array so that I can output the numbers: 2, 7, 32, 8, 2. Must I be initializing the values somehow? Little confused. I tried three four loops but different results. There is a link somewhat similar: Why is my simple Array only printing zeros in java? My code is below. Thank you in advanced.

 public class test
 {
     public static void main(String[] args) {
 

   int[] a = {2, 7, 32, 8, 2}; 
   int[] b = new int[a.length];  
   int[] c = new int[b.length];  
   int[][] d = {b}; 


     for(int z = 0; z < b.length; z++){
       System.out.print(b[z] + " ");
     } 

 System.out.println();

     for(int y = 0; y < c.length; y++){
       System.out.print(c.length + " ");
     }

 System.out.println();

     for(int x = 0; x < d.length; x++){
       System.out.print(d.length + " ");
     }


   }
 }
 
 ------------------------
 OUTPUT
 0 0 0 0 0
 5 5 5 5 5
 1

///////////////////////////

 //NEW CODE
 import java.util.*;

 public class Main {

   public static void main (String[]args) {

        int[] arr1 = {1, 2, 3, 4 };
        int[] arr2 = {5, 6, 7, 8, 9};
        int[] arr3 = {10, 11, 12};
        int[] arr4 = {13, 14, 15, 16, 17};
        int[][] arrOfarrs = {arr1, arr2, arr3, arr4};
        int a[] = new int[arrOfarrs.length];

        for (int z = 0; z < arrOfarrs.length; z++) {
          System.out.print (Arrays.toString (arrOfarrs[z]) + " ");
        a[z] = arrOfarrs[z][z];
        }

        System.out.println ();

   }
 }

Answer 1

There are two different operations with arrays in Java:

• initialization an array - when you create a new array with given size and default values (e.g. for int the default value is 0, for Object - null)

int[] arr = new int[5];  // i.e. arr = {0,0,0,0,0}

• write data into an array - when you put required date into created array

arr[0] = 2; arr[1] = 7; arr[2] = 32;
arr[3] = 8; arr[4] = 2;

Moreover, you can do both operations at the same time:

int[] arr = {2,7,32,8,2};

E.g. from your snippet:

int[] a = { 2, 7, 32, 8, 2 }; // create a new array with given values
int[] b = new int[a.length];  // create a new array with size 5 (a.length = 5) => b = {0,0,0,0,0};
int[] c = new int[b.length];  // create a new array with size 5 (b.length = 5) => c = {0,0,0,0,0};

And it's obvious this snippet will print content of an array b which is {0,0,0,0,0}

for (int id = 0; id < b.length; id++) {
    System.out.print(b[id] + " ");
}

And this one will print content of an array c which is {0,0,0,0,0}

for (int y = 0; y < c.length; y++) {
    System.out.print(c.length + " ");
}

About 2D array. In java this is nothing more than array of arrays. Each row is an array.

So when you init an array like this:

int[][] d = { b };

it means, that you define a 2D array with 1 row and this 1 row contain array b. By the way, each row in 2D array can have different length. I.e. in other way:

int[][] d = new int[1][];  // first [] is amount of rows, second - columns
d[0] = b;

To print 2D array you have to go through all rows (the first loop), and then all columns (the second loop).

for (int row = 0; row < d.length; row++) {
    for (int col = 0; col < d[row].length; col++) {
        System.out.print(d[row][col].length + " ");
    }

    System.out.println();
}