Topic 1.13 — Object Creation and Storage (Instantiation)

Goal: create objects using new, store object references in variables, and understand that variables can refer to different objects (or none).

The big idea

Instantiation means creating a new object. In Java, you usually create objects with the keyword new. The variable doesn’t store the whole object—it stores a reference to it.

Pattern: ClassName var = new ClassName(...);

Two-step thinking

Create an object (with new).
Store a reference to that object in a variable.

This is why we call these “reference variables” for objects.

Common syntax

// Declare a reference variable (doesn't create an object yet)
String s;

// Create + store in one line
s = new String("hi");

// Often shown as:
String t = new String("hello");

With String, you’ll also see literals like "hello" (that’s a special Java convenience).

Reference variables can change what they refer to

A reference variable can be reassigned to refer to a different object.

String s = new String("A");
s = new String("B");   // now s refers to a different object

`null` (no object)

A reference variable can hold null, which means it isn’t referring to any object.

String s = null;  // s refers to nothing

If you try to call a method on null, it causes an error (you’ll see this later).

Primitive vs. reference storage

Primitive

int x = 7;  // x stores 7 directly

Reference

String s = new String("hi");
// s stores a reference to the object

Exam mindset

new creates a new object.
Object variables store references (not the whole object).
Reassigning a reference variable changes what it points to.
null means “no object.”

Quick self-check

What does “instantiate” mean?
What does new do?
Does a reference variable store the object itself or a reference to it?
What does null mean?
Can a reference variable be reassigned to refer to a different object?

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