Can someone explain working of this code ?

Question

public class Program
{
public static void main(String[] args)
{
int a[][]= new int[4][];
a[0]= new int [1];
a[1]= new int [2];
a[2]= new int [3];
a[3]= new int [4];

int i,j,k=0;

for(i=0;i<4;i++)
for(j=0;j<i+1;j++)
{
a[i][j]=k;
k++;

}
for(i=0;i<4;i++)
{
for(j=0;j<i+1;j++)
System .out .print (a[i][j]+" ");
System .out .println ();
}
}
}

Answer 1

public class Program
{
public static void main(String[] args)
{
int a[][]= new int[4][]; //declaring array of 4 rows but not columns
a[0]= new int [1]; //declaring 0th row of 1 comumn
a[1]= new int [2]; //declaring 1st row of 2 comumn
a[2]= new int [3]; //declaring 2nd row of 3 comumn
a[3]= new int [4]; //declaring 3rd row of 4 comumn
int i,j,k=0;

for(i=0;i<4;i++) // you have 4 rows declared so you can use upto i<=3
for(j=0;j<i+1;j++) // colomns are 0,1,2,3 as above decakred
{
a[i][j]=k;
k++;
}

//printing only those values, which are you assigned
for(i=0;i<4;i++)
{
for(j=0;j<i+1;j++)
System .out .print (a[i][j]+" ");
System .out .println ();
}
}
}