Public access modifier in Java - Practice Problems & Coding Challenges

trophy

Challenge - 5 Problems

💻 code output

intermediate

Output of public method access from another class

What is the output of this Java program?

Java

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

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

A No output

B Compilation error: greet() is not accessible

C Runtime error: NullPointerException

D Hello from A

💻 code output

intermediate

Accessing public variable from another package

Given two packages pkg1 and pkg2, what is the output of the following code?

Java

package pkg1;
public class Data {
    public int number = 42;
}

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

A Compilation error: number is not accessible

B 42

C Runtime error: ClassNotFoundException

D 0

🔧 debug

advanced

Why does this public method cause a compilation error?

Consider the following code. Why does it cause a compilation error?

Java

class Parent {
    public void show() {
        System.out.println("Parent show");
    }
}

public class Child extends Parent {
    void show() {
        System.out.println("Child show");
    }
}

A Child's show() has weaker access than Parent's public show(), causing a compilation error

B Child's show() method is missing the @Override annotation

C Parent's show() method should be protected, not public

D No compilation error; code runs fine

📝 syntax

advanced

Identify the syntax error related to public modifier

Which option contains a syntax error related to the use of the public modifier?

A public class Example { public void method() {} }

B class Example { public int x; private void method() {} }

C public void method() { public int x = 5; }

D public interface Sample { void run(); }

🚀 application

expert

Effect of public modifier on class accessibility

Given the following code in two files, what will happen when compiling and running?

// File: pkg1/PublicClass.java
package pkg1;
public class PublicClass {
    public void display() {
        System.out.println("Visible everywhere");
    }
}

// File: pkg2/DefaultClass.java
package pkg2;
class DefaultClass {
    public void show() {
        System.out.println("Visible only in pkg2");
    }
}

// File: pkg2/TestAccess.java
package pkg2;
import pkg1.PublicClass;
public class TestAccess {
    public static void main(String[] args) {
        PublicClass pc = new PublicClass();
        pc.display();
        DefaultClass dc = new DefaultClass();
        dc.show();
    }
}

A Program runs and prints both messages

B Compilation error: Cannot access DefaultClass from another package

C Compilation error: DefaultClass is not public and cannot be accessed from TestAccess

D Runtime error: IllegalAccessException