Passing Arrays to Methods

Passing Arrays to Methods

1. Rule (beginner)

Arrays are objects → address-copy (shared!). Method CAN change elements (like objects!). Length fixed, content editable. Perfect for sort/fill helpers!

2. Code — Sort + Fill Change Original!

static void doubleAll(int[] a) {
    for (int i = 0; i < a.length; i++) a[i] *= 2; // edits SHARED boxes!
}
static void printAll(int[] a) {
    for (int x : a) System.out.print(x + " ");
}
public static void main(String[] args) {
    int[] m = {1, 2, 3};
    doubleAll(m);
    printAll(m); // 2 4 6 (changed! — proof!)
}

Varargs bonus (any count!):

static int sum(int... ns) { int s = 0; for (int n : ns) s += n; return s; }
sum(1,2); sum(1,2,3,4); // flexible!

3. Return Array? Yes!

static int[] first3() { return new int[]{1,2,3}; } // fresh array back!

4. Traps

• Reassign a = new int[5]; inside dies (like objects!). Edit elements to affect caller.
• arr.length (no ()!) inside method for safe loops.
• Passing null → NPE on a.length (check first!).

5. Exam Points

• Modify-in-method program — 5 marks, very frequent.
• Varargs + return-array — 3 marks, frequent.