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

Concept Flow - Public access modifier

Declare public class or member

↓

Accessible from anywhere

↓

Use in same class, package, or other packages

↓

No access restrictions

↓

Program runs

The public access modifier allows classes, methods, or variables to be accessed from any other class or package without restriction.

Execution Sample

Java

public class Car {
    public String model = "Tesla";
    public void display() {
        System.out.println(model);
    }

    public static void main(String[] args) {
        Car c = new Car();
        c.display();
    }
}

This code defines a public class with a public variable and method, then creates an object and calls the method to print the model.

Execution Table

Step	Action	Evaluation	Result
1	Create object c of class Car	new Car()	Object c created with model = "Tesla"
2	Call c.display()	c.display()	Prints: Tesla
3	Access c.model directly	c.model	Returns "Tesla"
4	Try access from another class/package	Access public member	Allowed, no error
5	End of execution	-	-

💡 Program ends after printing the model and demonstrating public access

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
c	null	Car object with model="Tesla"	Car object with model="Tesla"	Car object with model="Tesla"
model	null	"Tesla"	"Tesla"	"Tesla"

Key Moments - 2 Insights

Why can we access the variable 'model' directly from object 'c'?

Because 'model' is declared public, it can be accessed from any other class or package as shown in step 3 of the execution_table.

What happens if we try to access a non-public member from another package?

Access would be denied and cause a compile error, unlike public members which are accessible everywhere as shown in step 4.

Visual Quiz - 3 Questions

Look at the execution table, what is printed when c.display() is called at step 2?

A Error

B null

C Tesla

D Nothing

💡 Hint

Check the 'Result' column in step 2 of the execution_table.

At which step is the object 'c' created?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column for object creation in the execution_table.

If the variable 'model' was not public, what would happen at step 3?

A Access allowed

B Compile error

C Runtime error

D Variable becomes private automatically

💡 Hint

Refer to key_moments about access restrictions for non-public members.

Concept Snapshot

public modifier allows access from anywhere
Used on classes, methods, variables
No restrictions on visibility
Syntax: public type name
Example: public int count;

Full Transcript

The public access modifier in Java means that the class, method, or variable can be accessed from any other class or package without restriction. In the example, a public class Car has a public variable model and a public method display. When we create an object c of Car and call c.display(), it prints the model name 'Tesla'. Because model is public, we can also access c.model directly from anywhere. If a member is not public, accessing it from another package would cause a compile error. Public is the most open access level in Java.

Practice

1. What does the public access modifier mean in Java?

easy

A. The class, method, or variable is accessible from anywhere in the program.

B. The class, method, or variable is accessible only within its own class.

C. The class, method, or variable is accessible only within its own package.

D. The class, method, or variable is accessible only to subclasses.

Solution

1. Step 1: Understand the meaning of public

   The public modifier allows access from any other class in any package.

2. Step 2: Compare with other access levels

   Other modifiers like private or protected restrict access, but public is fully open.

3. Final Answer:

   The class, method, or variable is accessible from anywhere in the program. -> Option A

4. Quick Check:

   Public means open access [OK]

Hint: Public means accessible from anywhere in the program [OK]

Common Mistakes:

• Confusing public with private or protected
• Thinking public restricts access to package only
• Assuming public means only subclass access

2. Which of the following is the correct way to declare a public method in Java?

easy

A. void public myMethod() {}

B. public void myMethod() {}

C. private public void myMethod() {}

D. method public void myMethod() {}

Solution

1. Step 1: Recall Java method declaration syntax

   The access modifier comes first, then the return type, then the method name and parentheses.

2. Step 2: Check each option

   public void myMethod() {} follows correct syntax: public void myMethod() {}. Others have wrong order or invalid keywords.

3. Final Answer:

   public void myMethod() {} -> Option B

4. Quick Check:

   Access modifier first, then return type [OK]

Hint: Access modifier always comes before return type [OK]

Common Mistakes:

• Placing 'public' after 'void'
• Using invalid keywords like 'method'
• Combining multiple access modifiers incorrectly

3. What will be the output of the following Java code?

public class Test {
    public int number = 5;
    public static void main(String[] args) {
        Test obj = new Test();
        System.out.println(obj.number);
    }
}

medium

A. 5

B. 0

C. Compilation error

D. Runtime error

Solution

1. Step 1: Understand the public variable access

   The variable number is public and initialized to 5, so it can be accessed from main.

2. Step 2: Trace the program output

   The main method creates an object and prints obj.number, which is 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Public variable accessed correctly prints 5 [OK]

Hint: Public variables can be accessed directly from objects [OK]

Common Mistakes:

• Assuming default value 0 instead of initialized 5
• Thinking public causes errors
• Confusing static and instance variables

4. Identify the error in the following code snippet:

class Example {
    public int value;
}

public class Main {
    public static void main(String[] args) {
        Example ex = new Example();
        ex.value = 10;
        System.out.println(ex.value);
    }
}

medium

A. Class Example must be declared public to access its public variable.

B. Main class must not be public.

C. No error; code will compile and print 10.

D. Variable value must be private to be accessed.

Solution

1. Step 1: Check class and variable access

   Class Example is package-private but accessible within the same package. Its public variable value can be accessed.

2. Step 2: Verify main method usage

   Main creates Example object, assigns 10 to value, and prints it. This is valid.

3. Final Answer:

   No error; code will compile and print 10. -> Option C

4. Quick Check:

   Public variable accessible within same package [OK]

Hint: Public variables accessible within same package without public class [OK]

Common Mistakes:

• Thinking class must be public to access public members
• Confusing variable access with class access
• Assuming private needed for access

5. You want to create a Java class with a public method that can be called from any other class, but the class itself should only be accessible within its package. Which of the following is correct?

hard

A. Declare both the class and method as public.

B. Declare the class as private and the method as public.

C. Declare the class as public and the method as private.

D. Declare the class without public and the method as public.

Solution

1. Step 1: Understand class access modifiers

   Classes without public are package-private, so accessible only within the package.

2. Step 2: Understand method access modifiers

   Methods declared public inside a package-private class are accessible from other classes in the same package.

3. Step 3: Analyze options

   Declare the class without public and the method as public. matches the requirement: class package-private, method public. Declare both the class and method as public. makes class public (accessible everywhere). Declare the class as public and the method as private. hides method. Declare the class as private and the method as public. is invalid because classes cannot be private.

4. Final Answer:

   Declare the class without public and the method as public. -> Option D

5. Quick Check:

   Class package-private + public method = accessible in package [OK]

Hint: Class without public is package-private; method public means accessible inside package [OK]

Common Mistakes:

• Thinking class can be private
• Assuming public class needed for public method
• Confusing method access with class access