How to find number of element in an Array in java?

Question

I want to know that how can i find the number of element in the normal array in java. For example if i have an int array with size 10 and i have inserted only 5 element. Now, i want to check the number of element in my array? Below is the code for more clarification. Please help

public static void main(String[] args) {

        int [] intArray = new int[10];
        char [] charArray = new char[10];

        int count = 0;

        for(int i=0; i<=5; i++) {

            intArray[i] = 5;    
            charArray[i] = 'a';


        }


        for(int j=0; j<=intArray.length; j++) {
            if(intArray[j] != null) {
                count++;
            }
        }

        System.out.println("int Array element : "+ count);
    }

Answer 1

The code is wrong. You declare a int[] : this cannot contain null values so this statement will not compile :

if(intArray[j] != null) {

Then, if you want to store many items but you don't know howmany, you should use a Collection, for example ArrayList

List<Integer> ints = new ArrayList<Integer>(); //Or new ArrayList<>(); - Java7

Then, you can have the size with :

ints.size();

Now, if you really want to use an array, then you can for example count the number of non-zero values :

for(int j=0; j<=intArray.length; j++) {
  if(intArray[j] != 0) {
    count++;
  }
}

Or better in Java 7 :

for(int i : intArray) {
  if(i!=0) {
    count++;
  }
}

Even better in Java 8 :

Arrays.stream(intArray).filter(i -> i !=0).count();

Answer 2

Check out Collection.frequency(). This will count how many times the specific Object (in this case null) appears in the Collection.

Below is just an example to help you along

String[] array = new String[5];

array[0] = "This";
array[1] = null;
array[2] = "is";
array[3] = null;
array[4] = "a test";

int count = Collections.frequency(Arrays.asList(array), null);

System.out.println("String: " + count + " items out of " + array.length + " are null");

int[] iArray = new int[3];
iArray[0] = 0;
iArray[1] = 1;
iArray[2] = 2;

List<Integer> iList = new ArrayList<>();

for (int i : iArray) {
    iList.add(i);
}

int iCount = Collections.frequency(iList, 0);

System.out.println("Int: " + iCount + " items out of " + iArray.length + " are zero");

char[] cArray = new char[3];
cArray[0] = 'c';
cArray[1] = ' ';
cArray[2] = 'a';

List<Character> cList = new ArrayList<>();

for (char c : cArray) {
    cList.add(c);
}

int cCount = Collections.frequency(cList, ' ');

System.out.println("Char: " + cCount + " items out of " + cArray.length + " are ' '");

Output:

String: 2 items out of 5 are null
Int: 1 items out of 3 are zero
Char: 1 items out of 3 are ' '