Object creation in Java - Step-by-Step Execution

Concept Flow - Object creation

Class Definition

↓

Call new Keyword

↓

Allocate Memory

↓

Call Constructor

↓

Initialize Object

↓

Return Object Reference

↓

Use Object

This flow shows how Java creates an object: define class, use 'new' to allocate memory, call constructor to initialize, then get a reference to use.

Execution Sample

Java

class Dog {
  String name;
  Dog(String n) { name = n; }
}
Dog d = new Dog("Buddy");

Creates a Dog object named Buddy and stores its reference in variable d.

Execution Table

Step	Action	Evaluation	Result
1	Define class Dog	Class Dog available	Dog class ready
2	Call new Dog("Buddy")	Allocate memory for Dog object	Memory allocated
3	Call Dog constructor with "Buddy"	Set name = "Buddy"	Object initialized with name="Buddy"
4	Assign object reference to d	d points to new Dog object	d references Dog object
5	Use d.name	Access name field	"Buddy" returned

💡 Object created and reference stored in d; program can now use d to access Dog's data.

Variable Tracker

Variable	Start	After Step 4	Final
d	null	reference to Dog object	reference to Dog object
Dog.name	N/A	N/A	"Buddy"

Key Moments - 3 Insights

Why do we use the 'new' keyword when creating an object?

The 'new' keyword allocates memory and calls the constructor to create the object, as shown in steps 2 and 3 of the execution_table.

What does the variable 'd' hold after object creation?

Variable 'd' holds a reference (or address) to the Dog object in memory, not the object itself, as shown in step 4.

How is the object's field 'name' set to "Buddy"?

The constructor Dog(String n) sets the field 'name' to "Buddy" during initialization in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what happens at step 3?

A Memory is allocated for the Dog object

B The Dog constructor sets the name field

C The variable d is assigned the object reference

D The class Dog is defined

💡 Hint

Check the 'Action' and 'Result' columns at step 3 in the execution_table.

At which step does the variable 'd' get assigned the object reference?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Action' column for assignment to d in the execution_table.

If we remove the 'new' keyword, what would happen to the variable 'd'?

A d would still reference a Dog object

B d would hold the string "Buddy"

C d would be null or cause a compile error

D d would hold the constructor itself

💡 Hint

Recall that 'new' allocates memory and creates the object; without it, no object is created.

Concept Snapshot

Object creation in Java:
- Use 'new ClassName(args)' to create an object.
- 'new' allocates memory and calls the constructor.
- Constructor initializes object fields.
- Variable stores reference to the object.
- Access fields via the reference variable.

Full Transcript

In Java, creating an object involves defining a class, then using the 'new' keyword to allocate memory and call the constructor. The constructor sets up the object's data. The variable on the left side holds a reference to this new object. For example, 'Dog d = new Dog("Buddy");' creates a Dog object named Buddy and stores its reference in d. Step-by-step, the class is ready, memory is allocated, the constructor sets the name, and d points to the object. This process allows the program to use the object through the reference variable.