Default access modifier in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of default access modifier in same package

What is the output of this Java code when both classes are in the same package?

Java

class A {
    int number = 10; // default access
}

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

A 10

B Compilation error: number has private access in A

C Compilation error: number is not public in A

D Runtime error

💡 Hint

Default access allows access within the same package.

The variable 'number' has default access, so it is accessible within the same package. Since both classes are in the same package, the code prints 10.

❓ Predict Output

intermediate

Accessing default member from different package

What happens when you try to access a default access member from a class in a different package?

Java

package pkg1;
class B {
    int value = 5; // default access
}

package pkg2;
import pkg1.B;
public class Test {
    public static void main(String[] args) {
        B b = new B();
        System.out.println(b.value);
    }
}

A 5

B Compilation error: value is not public in B

C Compilation error: B() has private access in B

D Runtime error: IllegalAccessException

💡 Hint

Default access members are not visible outside their package.

The member 'value' has default access and is not visible outside its package. Trying to access it from another package causes a compilation error.

🔧 Debug

advanced

Why does this code fail to compile?

This code tries to access a default access method from another package. Identify the cause of the compilation error.

Java

package pkg1;
class C {
    void show() { System.out.println("Hello"); } // default access
}

package pkg2;
import pkg1.C;
public class Test {
    public static void main(String[] args) {
        C c = new C();
        c.show();
    }
}

A Class C is abstract and cannot be instantiated

B Class C is public but method show() is private

C Method show() has default access and is not visible outside pkg1

D Method show() is static and should be called on class

💡 Hint

Check the access level of method show() and package visibility.

The method show() has default access, so it is only accessible within the same package. Since Test is in a different package, the call c.show() causes a compilation error.

🧠 Conceptual

advanced

Default access modifier and subclassing

If a class with default access modifier is subclassed in the same package, can the subclass access the default members of the superclass?

A No, default members are only accessible within the same class

B No, default members are not accessible to subclasses even in the same package

C Yes, but only if the subclass is in a different package

D Yes, default members are accessible to subclasses in the same package

💡 Hint

Think about package-level visibility and inheritance.

Default access members are accessible anywhere within the same package, including subclasses. So subclasses in the same package can access default members.

❓ Predict Output

expert

Number of accessible members with default access

Given this class with default access members, how many members are accessible from another class in the same package?

Java

class D {
    int a = 1; // default
    private int b = 2;
    protected int c = 3;
    public int d = 4;
}

A 3

B 4

C 2

D 1

💡 Hint

Remember which access modifiers allow access within the same package.

From the same package, default, protected, and public members are accessible. Private members are not accessible. So members a, c, and d are accessible, total 3.

Practice

1. Which statement best describes the default access modifier in Java?

easy

A. It restricts access only to the class itself.

B. It allows access from any package using the default keyword.

C. It allows access only within the same package without using any keyword.

D. It allows access only to subclasses in other packages.

Solution

1. Step 1: Understand default access modifier meaning

   The default access modifier means no keyword is used before a class, method, or variable, and it restricts access to the same package only.

2. Step 2: Compare options with definition

   It allows access only within the same package without using any keyword. correctly states it allows access only within the same package and requires no keyword. Other options mention keywords or access outside the package, which is incorrect.

3. Final Answer:

   It allows access only within the same package without using any keyword. -> Option C

4. Quick Check:

   Default access = package-only access [OK]

Hint: No keyword means default access is package-only [OK]

Common Mistakes:

• Thinking default requires a keyword
• Confusing default with public or private
• Assuming default allows access from other packages

2. Which of the following is the correct way to declare a class with default access modifier?

easy

A. class MyClass {}

B. private class MyClass {}

C. default class MyClass {}

D. public class MyClass {}

Solution

1. Step 1: Recall syntax for default access modifier

   Default access means no access keyword is written before the class name.

2. Step 2: Check each option

   class MyClass {} declares the class without any access keyword, which means default access. Options A and B use explicit keywords, and C uses a non-existent keyword.

3. Final Answer:

   class MyClass {} -> Option A

4. Quick Check:

   No keyword = default access [OK]

Hint: No keyword before class means default access [OK]

Common Mistakes:

• Using 'default' keyword which does not exist in Java
• Confusing private with default
• Always using public by habit

3. Consider two classes in the same package:

class A {
    void show() {
        System.out.println("Hello from A");
    }
}

class B {
    public static void main(String[] args) {
        A a = new A();
        a.show();
    }
}

What will be the output when class B is run?

medium

A. Compile-time error: show() has private access

B. Hello from A

C. Compile-time error: class A is not public

D. Runtime error

Solution

1. Step 1: Analyze access modifiers in the code

   Class A and method show() have default access (no keyword). Both classes are in the same package, so access is allowed.

2. Step 2: Predict program output

   Since B can access A and its show() method, the program prints "Hello from A" without errors.

3. Final Answer:

   Hello from A -> Option B

4. Quick Check:

   Default access allows same package access [OK]

Hint: Default access works within same package [OK]

Common Mistakes:

• Assuming default means private access
• Thinking class A must be public to be used
• Confusing compile-time and runtime errors

4. Given two packages pkg1 and pkg2, and these classes:

package pkg1;
class C {
    void display() {
        System.out.println("Inside C");
    }
}

package pkg2;
import pkg1.C;
public class D {
    public static void main(String[] args) {
        C c = new C();
        c.display();
    }
}

What is the error in this code?

medium

A. Cannot access class C from pkg2 because it has default access

B. Cannot call display() because it is private

C. Cannot import package pkg1

D. No error, code runs fine

Solution

1. Step 1: Check class C's access modifier and package

   Class C has default access (no keyword) and is in package pkg1, so it is accessible only within pkg1.

2. Step 2: Check usage of C in pkg2

   Class D in pkg2 tries to create an instance of C and call display(), but C is not visible outside pkg1, causing a compile-time error.

3. Final Answer:

   Cannot access class C from pkg2 because it has default access -> Option A

4. Quick Check:

   Default access = package-only visibility [OK]

Hint: Default access blocks cross-package access [OK]

Common Mistakes:

• Assuming default access allows cross-package use
• Thinking display() is private
• Confusing import errors with access errors

5. You have a package tools with classes:

class Helper {
    void assist() {
        System.out.println("Helping...");
    }
}

public class Tool {
    public static void main(String[] args) {
        Helper h = new Helper();
        h.assist();
    }
}

You want to allow only classes inside tools to use Helper and its assist() method, but prevent access from outside. Which is the best way to achieve this?

hard

A. Make Helper and assist() public.

B. Use protected for Helper and assist().

C. Make Helper and assist() private.

D. Keep Helper and assist() with default access (no keyword).

Solution

1. Step 1: Understand access goals

   You want Helper and assist() accessible only inside the same package (tools) and hidden outside.

2. Step 2: Match access modifiers to goals

   Default access (no keyword) restricts access to the same package only, which fits the requirement. Public allows all access, private restricts to the class only, and protected allows subclasses and package access.

3. Final Answer:

   Keep Helper and assist() with default access (no keyword). -> Option D

4. Quick Check:

   Default access = package-only visibility [OK]

Hint: Default access hides from outside packages [OK]

Common Mistakes:

• Using public which exposes to all packages
• Using private which hides even inside package
• Using protected which allows subclass access outside package