Best practices in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Java code snippet?

Consider the following Java code. What will it print when run?

Java

public class Test {
    public static void main(String[] args) {
        int x = 5;
        int y = 10;
        int result = x > y ? x : y;
        System.out.println(result);
    }
}

A 5

B Runtime exception

C 10

D Compilation error

💡 Hint

Look at the ternary operator and which value it selects.

The ternary operator checks if x > y. Since 5 > 10 is false, it selects y, which is 10.

🧠 Conceptual

intermediate

Which practice improves code readability in Java?

Which of the following is considered a best practice to improve code readability in Java?

A Using meaningful variable names like <code>totalPrice</code> instead of <code>tp</code>

B Writing all code in one long method without comments

C Using single-letter variable names for all variables

D Avoiding indentation to save space

💡 Hint

Think about what helps someone else understand your code easily.

Meaningful variable names make code easier to read and maintain. The other options reduce readability.

🔧 Debug

advanced

What error does this Java code produce?

Examine the code below. What error will occur when compiling?

Java

public class Demo {
    public static void main(String[] args) {
        final int number;
        System.out.println(number);
    }
}

A Runtime exception: NullPointerException

B Compilation error: variable number might not have been initialized

C Compilation error: cannot assign a value to final variable number

D No error, prints 0

💡 Hint

Consider what happens if a final variable is declared but not assigned before use.

The final variable 'number' is declared but never initialized. Java requires final variables to be assigned before use.

📝 Syntax

advanced

Which option correctly declares a Java record?

Which of the following is the correct syntax to declare a record named Person with fields String name and int age?

A public record Person { String name; int age; }

B public class Person(String name, int age) {}

C record Person { String name; int age; }

D public record Person(String name, int age) {}

💡 Hint

Recall the syntax introduced in Java 16 for records.

Records are declared with the record keyword followed by the name and a parameter list in parentheses.

🚀 Application

expert

How many items are in the resulting Map after running this code?

What is the size of the map after executing the following Java code?

Java

import java.util.*;
public class MapTest {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("a", 1);
        map.put("b", 2);
        map.put("a", 3);
        map.put("c", 4);
        map.put("b", 5);
        System.out.println(map.size());
    }
}

A 3

B 5

C 4

D 2

💡 Hint

Remember how keys behave in a Map when duplicated.

Keys in a Map are unique. Adding a key again replaces the old value, so the final map has keys "a", "b", and "c" only.