create a method that can count negative numbers in an array

Try giving a return statement , your method is expecting a int as a return parameter. Therefore it will give compiler error.

public class negativeTest {

    public static int Negativenum (int[] array) {

        int negative = 0;
        for (int i = 0; i < array.length; i++){
            if(array[i] < 0){
                negative = negative + 1;
            }
            System.out.println(negative);

        }
      return negative;
    }

}

Ther error you are getting is because you have not declared the main function inside the class.

You have to call Negativenum from the main function.

you can do it like this :

 public static void main (String args[])
 {
 negativeTest  nt = new negativeTest();
 int [] array = new int[]{ 100,200 };  
 int count = nt.Negativenum(array);
 System.out.println(count);  // It will print **2** 
 }

Regarding your doubts you have asked in comments.

You have to return anything from function only when you want to use that use that return value from the calling function. Otherwise if you want to just print that value on console or log that value , you can easily do it in the negativeTest function and you can change the return type of this function to void.

FYI , you should not begin your classname with the lower case character.

The error is because you are not returning anything from the function which is expected to return an int.

If you want the function to count the number of negative numbers and return the count so that the caller of the function gets the count, you can add an

return negative;

before the end of the function.

Alternatively if you don't want to return anything from the function and want to just print the count as part of the function call, you can change the return type of the function from int to void:

public static void Negativenum (int[] array) {

Your function signature suggest a return type of int, but you aren't returning anything from the function. I suspect this is why Eclipse is suggesting you change the function signature to return void.

If you add return negative; it should avoid the notice from Eclipse.

If your intention is to simply print the count, then you should change the return type.

if you dont want to return anything, set your method signature to void, but add an out variable, like so:

public static void NegativeNum(int[] array, out int negative)
{
     negative = 0;
     foreach(int i in array) { if (i < 0) negative++;
}

then you just declare negative wherever this method is called from, and pass it in as an out variable:

int negative = 0;
NegativeNum(array, out negative);

After that call, negative will contain the count of negative numbers determined by the method.