New Operator

New Operator

1. What new Does (beginner)

new creates an object/array on the Heap and returns its address. Without new, reference variables point to null (nothing). Think: new = "build me a house, give me its address".

2. Code — Without vs With new

String s;            // declares address box, holds null (no object yet!)
// s.length();       // NullPointerException! (no house built)
s = new String("hi"); // NOW built on Heap, s holds address
System.out.println(s.length()); // 2 — works!

int[] arr = new int[3]; // array of 3 zeros on Heap: [0,0,0]
arr[0] = 10;
Student st = new Student(); // calls constructor (see Module 2)

Steps of new Student(): allocate Heap memory → run constructor → return address into st.

3. Primitives Don't Need new

int x = 5; lives on Stack directly. Objects/arrays need new (Heap). String is special: "hi" auto-creates (no new needed, but new String("hi") also works).

4. Traps

• NullPointerException = forgot new (most common beginner crash!).
• new int[3] elements auto-zero; new String[3] elements auto-null.
• Memory freed by GC (no delete like C++).

5. Exam Points

• What new does (Heap + constructor + address) — 5 marks, very frequent.
• NullPointerException cause + fix — 3 marks, frequent.