Java String array: is there a size of method?

Question

I come from a php background and in php, there is an array_size() function which tells you how many elements in the array are used.

Is there a similar method for a String[] array? Thanks.

Answer 1

Yes, .length (property-like, not a method):

String[] array = new String[10];
int size = array.length;

Answer 2

array.length

It is actually a final member of the array, not a method.

Answer 3

Also, it's probably useful to note that if you have a multiple dimensional Array, you can get the respective dimension just by appending a '[0]' to the array you are querying until you arrive at the appropriate axis/tuple/dimension.

This is probably better explained with the following code:

public class Test {
    public static void main(String[] args){
        String[][] moo = new String[5][12];

        System.out.println(moo.length); //Prints the size of the First Dimension in the array
        System.out.println(moo[0].length);//Prints the size of the Second Dimension in the array
    }

}

Which produces the output:

5
12

Answer 4

array.length final property

it is public and final property. It is final because arrays in Java are immutable by size (but mutable by element's value)

Answer 5

Arrays are objects and they have a length field.

String[] haha = {"olle", "bulle"};

haha.length would be 2

Answer 6

In java there is a length field that you can use on any array to find out it's size:

    String[] s = new String[10];
    System.out.println(s.length);

Answer 7

If you want a function to do this

Object array = new String[10];
int size = Array.getlength(array);

This can be useful if you don't know what type of array you have e.g. int[], byte[] or Object[].

Answer 8

There is a difference between length of String and array to clarify:

int a[] = {1, 2, 3, 4};
String s = "1234";

a.length //gives the length of the array

s.length() //gives the length of the string

Answer 9

The answer is "All of them". A java array is allocated with a fixed number of element slots. The "length" attribute will tell you how many. That number is immutable for the life of the array. For a resizable equivalent, you need one of the java.util.List classes - where you can use the size() method to find out how many elements are in use.

However, there's "In use" and then there's In Use. In an class object array, you can have element slots whose elements are null objects, so even though they count in the length attribute, but most people's definitions, they're not in use (YMMV, depending on the application). There's no builtin function for returning the null/non-null counts.

List objects have yet another definition of "In Use". To avoid excessive creation/destruction of the underlying storage structures, there's typically some padding in these classes. It's used internally, but isn't counted in the returned size() method. And if you attempt to access those items without expanding the List (via the add methods), you'll get an illegal index exception.

So for Lists, you can have "In Use" for non-null, committed elements, All committed elements (including null elements), or All elements, including the expansion space presently allocated.

Answer 10

All the above answers are proper. The important thing to observe is arrays have length attribute but not length method. Whenever you use strings and arrays in java the three basic models you might face are:

1. String s=new String("vidyasagar");
   System.out.println(s.length()); // In this case we are using only String. No length attribute for Strings. we have to use length() method.
2. int[] s=new int[10]; System.out.println(s.length); //here we use length attribute of arrays.
3. String[] s=new String[10];
   System.out.println(s.length); // Here even though data type is String, it's not a single String. s is a reference for array of Strings. So we use length attribute of arrays to express how many strings can fit in that array.

Answer 11

Not really the answer to your question, but if you want to have something like an array that can grow and shrink you should not use an array in java. You are probably best of by using ArrayList or another List implementation.

You can then call size() on it to get it's size.