Creating packages in Java - Practice Exercises

trophy

Challenge - 5 Problems

💻 code output

intermediate

Output of Java package usage

What is the output of the following Java code when run?

Java

package com.example.utils;

public class Helper {
    public static String greet() {
        return "Hello from Helper!";
    }
}

// In another file:
package com.example.app;

import com.example.utils.Helper;

public class Main {
    public static void main(String[] args) {
        System.out.println(Helper.greet());
    }
}

A Hello from Helper!

B Compilation error: cannot find symbol Helper

C Runtime error: NoClassDefFoundError

D Hello from Main!

💻 code output

intermediate

Effect of missing package declaration

What happens if you remove the package declaration from a Java file that is supposed to be in a package?

Java

package mypkg;

public class Test {
    public static void main(String[] args) {
        System.out.println("In package mypkg");
    }
}

// Now remove the line 'package mypkg;' and compile and run.

A The program runs and prints 'In package mypkg'

B Compilation error: class not found in package

C Runtime error: ClassNotFoundException

D The program runs but prints nothing

🔧 debug

advanced

Identify the cause of compilation error with packages

Why does the following code cause a compilation error?

Java

package com.example;

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

// In file B.java:
package com.example.other;

public class B {
    public void sayHi() {
        System.out.println("Hi from B");
    }
}

A Class B's method sayHi is static but called on instance

B Class B is not public

C Class A does not import com.example.other.B

D Class A and B must be in the same package

📝 syntax

advanced

Correct package declaration syntax

Which of the following is the correct way to declare a package in a Java file?

A package com.example.utils

B package com.example.utils;

C package com.example.utils()

D package com.example.utils {}

🚀 application

expert

Number of classes accessible without import

Given these two packages and classes, how many classes can class Main access directly without import statements?

Java

package alpha;
public class A {}
public class B {}

package beta;
public class C {}

package alpha;
public class Main {
    public static void main(String[] args) {
        // How many of A, B, C can be used here without import?
    }
}

A 0 classes

B 3 classes (A, B, and C)

C 1 class (A only)

D 2 classes (A and B)