Array Declaration and Initialization in Java

Direct Answer

Declare an array with Type[] name. Create it with new Type[length], or supply values in an initializer such as int[] scores = {90, 80}. A newly created array is fixed in length and its elements receive defaults: numeric zero, false, the null character for char, and null for reference elements. array.length is a field.

Code Example

Each declaration style fits a different situation, and the snippet below also proves the two facts interviewers probe: Java zero-fills automatically, and length is a field. Run it as a plain Java 17 console app.

public class ArrayDemo {
    public static void main(String[] args) {

        // Style 1: declare size, fill later
        int[] scores = new int[5];
        System.out.println(scores[0]); // 0  — Java zero-fills automatically

        scores[0] = 95;
        scores[1] = 72;
        // scores[2], [3], [4] remain 0

        // Style 2: declare and initialize with values in one line
        String[] days = {"Mon", "Tue", "Wed", "Thu", "Fri"};
        System.out.println(days[0]); // Mon

        // Style 3: new keyword with explicit values (useful when size is computed)
        double[] prices = new double[]{9.99, 14.50, 3.75};

        // Length is a field — no parentheses
        System.out.println(scores.length); // 5
        // System.out.println(scores.length()); // COMPILE ERROR — common mistake

        // Default for object arrays is null, not empty string
        String[] names = new String[3];
        System.out.println(names[0]); // null
    }
}

Notice the two traps in one place: scores.length() would refuse to compile, and names[0] is null rather than an empty string — object arrays default to null, not to a "blank" value.

Common Mistakes & Pitfalls

• Writing arr.length() — length is a field on an array, not a method, so the parentheses are a compile error. Only String uses length(); arrays use arr.length.
• Expecting garbage values — beginners coming from C sometimes add code to "clear" a new array first. Java already zero-fills every slot (0, false, null), so that work is wasted.
• Indexing an array you only declared — a field left as int[] arr; is null, and arr[0] = 1 throws NullPointerException, not an empty-array error. You must assign with new (or a literal) before indexing.
• Reading index length — a 5-element array's last valid index is 4; arr[arr.length] always throws ArrayIndexOutOfBoundsException because indices run 0 to length - 1.