Java arrays are the ancestors of ArrayLists…
Arrays
Unlike the newer and younger ArrayLists, arrays come with Java by default. You don’t have to take the trouble of importing, creating object and then getting it work!
Refer OOP if you don’t know what’s an object.
Creating an array
We can create an array by two ways :
- We create it with the elements
- We specify the datatype and size to add them later.
String[] brands = {"espresso", "java", "latte"};
String[] brands = new String[2];
Array operations
We usually use the array’s index to add, access, modify and delete elements.
//adding elements
brands[0] = "espresso";
brands[1] = "java";
//modifying elements
brands[0] = "latte";
//accessing elements
System.out.println(array[0]);
System.out.println(array[1]);
Sometimes, we’d want to access the end of the list. We can already do this in ArrayList using IndexOf(), but now we want to do it with arrays.
Negative indices with Java
Let’s try using negative indices like we do with Python…
public class neg
{
public static void main(String[] args)
{
String[] brands = {"espresso", "java", "latte"};
System.out.println(brands[-1]);
}
}
Why did we get an exception when all’s going well? Oh well, all’s not going well, it seems.
Java doesn’t support negative indices.
It’s because arrays in Java [and also C, C++, etc.] are stored in contiguous [unbroken, continuous] blocks of memory.
When we access array elements, the language uses pointer arithmetic to calculate the memory address of the element [thus locating it].
If we access an element using a negative index, the language will try to access memory before the array even begins! This leads to a sweet struggle before a likely runtime error.
Source -> Quora
Now to access the last element in a java-proper manner, we use this workaround :
int index = brands.length - 1;
length is not a method call. Don’t use it like length().