Question: Consider:

```
int[][] multD = new int[5][];
multD[0] = new int[10];

```

Is this how you create a two-dimensional array with 5 rows and 10 columns?

I saw this code online, but the syntax didn't make sense.

Answer: 
These types of arrays are known as jagged arrays in Java:

```
int[][] multD = new int[3][];
multD[0] = new int[3];
multD[1] = new int[2];
multD[2] = new int[5];

```

In this scenario each row of the array holds the different number of columns. In the above example, the first row will hold three columns, the second row will hold two columns, and the third row holds five columns. You can initialize this array at compile time like below:

```
 int[][] multD = {{2, 4, 1}, {6, 8}, {7, 3, 6, 5, 1}};

```

You can easily iterate all elements in your array:

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

```
If you want something that's dynamic and flexible (i.e. where you can add or remove columns and rows), you could try an "ArrayList of ArrayList":

```java
public static void main(String[] args) {

    ArrayList<ArrayList<String>> arrayListOfArrayList = new ArrayList<>();

    arrayListOfArrayList.add(new ArrayList<>(List.of("First", "Second", "Third")));
    arrayListOfArrayList.add(new ArrayList<>(List.of("Fourth", "Fifth", "Sixth")));
    arrayListOfArrayList.add(new ArrayList<>(List.of("Seventh", "Eighth", "Ninth")));
    arrayListOfArrayList.add(new ArrayList<>(List.of("Tenth", "Eleventh", "Twelfth")));

    displayArrayOfArray(arrayListOfArrayList);
    addNewColumn(arrayListOfArrayList);
    displayArrayOfArray(arrayListOfArrayList);
    arrayListOfArrayList.remove(2);
    displayArrayOfArray(arrayListOfArrayList);
}

private static void displayArrayOfArray(ArrayList<ArrayList<String>> arrayListOfArrayList) {
    for (int row = 0; row < arrayListOfArrayList.size(); row++) {
        for (int col = 0; col < arrayListOfArrayList.get(row).size(); col++) {
            System.out.printf("%-10s", arrayListOfArrayList.get(row).get(col));
        }
        System.out.println("");
    }
    System.out.println("");
}

private static void addNewColumn(ArrayList<ArrayList<String>> arrayListOfArrayList) {
    for (int row = 0; row < arrayListOfArrayList.size(); row++) {
        arrayListOfArrayList.get(row).add("added" + row);
    }
}

```

Output:

```
First     Second    Third     
Fourth    Fifth     Sixth     
Seventh   Eighth    Ninth     
Tenth     Eleventh  Twelfth   

First     Second    Third     added0    
Fourth    Fifth     Sixth     added1    
Seventh   Eighth    Ninth     added2    
Tenth     Eleventh  Twelfth   added3    

First     Second    Third     added0    
Fourth    Fifth     Sixth     added1    
Tenth     Eleventh  Twelfth   added3    

```