Private access modifier in Java - Step-by-Step Execution

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Concept Flow - Private access modifier

Class with private member

↓

Access private member inside class?

No→Error if accessed outside

Yes↓

Access allowed, use member

↓

End

The private modifier restricts access to class members only within the class itself.

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Execution Sample

Java

class Box {
  private int size = 5;
  int getSize() {
    return size;
  }
}

public class Main {
  public static void main(String[] args) {
    Box b = new Box();
    System.out.println(b.getSize());
  }
}

This code shows a private variable accessed inside the class via a public method.

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Execution Table

Step	Action	Evaluation	Result
1	Create Box object b	Box object with size=5	b.size is private, stored as 5
2	Call b.getSize()	Inside getSize(), access private size	Returns 5
3	Print returned value	Output value	5
4	Try to access b.size directly (not shown in code)	Compile error	Cannot access private field
5	End	-	-

💡 Execution stops after printing 5; direct access to private field is not allowed.

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Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
b.size	undefined	5	5	5

key

Key Moments - 2 Insights

▶Why can't we access b.size directly outside the class?

▶How does the getSize() method access the private variable?

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Visual Quiz - 3 Questions

Look at the execution_table, what value does getSize() return at step 2?

A 0

B 5

C Compile error

D null

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Concept Snapshot

private modifier:
- Used to restrict access to class members
- Members are accessible only inside their own class
- Outside access causes compile errors
- Use public methods to access private members
- Helps protect data and enforce encapsulation

contract

Full Transcript

This example shows how the private access modifier works in Java. A class Box has a private variable size set to 5. Inside the class, a method getSize() returns this private variable. When we create an object b of Box and call b.getSize(), it returns 5. However, trying to access b.size directly outside the class causes a compile error because size is private. This protects the variable from outside access. To get the value, we use a public method inside the class. This is how private access modifier helps keep data safe and controlled.