Private data members in Java - Step-by-Step Execution

Concept Flow - Private data members

Class with private data members

↓

Create object of class

↓

Try to access private member directly?

Yes→Error: Not accessible

No↓

Use public method to access private member

↓

Get or set private data safely

↓

End

Private data members are hidden inside a class. They cannot be accessed directly from outside. Instead, public methods are used to get or set their values safely.

Execution Sample

Java

class Person {
  private String name;
  public Person(String name) { this.name = name; }
  public String getName() { return name; }
}

Person p = new Person("Anna");
System.out.println(p.getName());

This code creates a Person object with a private name and prints the name using a public method.

Execution Table

Step	Action	Variable/Member	Value	Result/Output
1	Create Person object with name 'Anna'	p.name	private, set to 'Anna'	Object p created
2	Call p.getName()	p.name	Anna	Returns 'Anna'
3	Print returned value	-	-	Anna
4	Try to access p.name directly	p.name	Error	Compilation error: name has private access in Person

💡 Direct access to private member 'name' is not allowed; must use public methods.

Variable Tracker

Variable/Member	Start	After Object Creation	After getName Call	Final
p.name	null	Anna	Anna	Anna

Key Moments - 2 Insights

Why can't we access p.name directly from outside the class?

Because 'name' is declared private, it is hidden from outside code. The execution_table row 4 shows a compilation error when trying direct access.

How do we get the value of a private data member?

We use a public method like getName() that returns the private member's value, as shown in execution_table row 2.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of p.name after object creation?

A "Anna"

B null

C Error

D "name"

💡 Hint

Check execution_table row 1 under 'Value' column.

At which step does the program print the name 'Anna'?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at execution_table row 3 under 'Result/Output'.

What happens if you try to access the private member directly as in step 4?

A It prints the value

B It returns null

C Compilation error

D It changes the value

💡 Hint

See execution_table row 4 for the result of direct access.

Concept Snapshot

Private data members are declared with 'private' keyword.
They cannot be accessed directly outside the class.
Use public methods (getters/setters) to read or modify them.
This protects data and controls access.
Trying direct access causes a compile-time error.

Full Transcript

Private data members in Java are variables inside a class marked with the keyword 'private'. This means they cannot be accessed directly from outside the class. Instead, we create public methods called getters and setters to read or change these private variables safely. For example, a class Person has a private String name. We create a public method getName() that returns the name. When we create a Person object with name 'Anna' and call getName(), it returns 'Anna'. If we try to access the private name directly, the program will not compile and shows an error. This protects the data inside the class and controls how it is accessed or changed.