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.

Practice

1. Which of the following is a best practice for naming variables in Java?

easy

A. Use clear and meaningful names like totalPrice instead of tp

B. Use single letters like x or y for all variables

C. Use all uppercase letters for variable names

D. Use names with special characters like total$price

Solution

1. Step 1: Understand variable naming clarity

   Clear and meaningful names help others understand the code easily.

2. Step 2: Compare options

   Use clear and meaningful names like totalPrice instead of tp uses descriptive names, while others use unclear or invalid styles.

3. Final Answer:

   Use clear and meaningful names like totalPrice instead of tp -> Option A

4. Quick Check:

   Meaningful variable names = Use clear and meaningful names like totalPrice instead of tp [OK]

Hint: Choose names that explain the variable's purpose [OK]

Common Mistakes:

• Using single letters for all variables
• Using uppercase for variable names (reserved for constants)
• Including special characters in names

2. Which of the following Java code snippets follows best practices for defining constants?

easy

A. int MAX_SIZE = 100;

B. final int maxSize = 100;

C. final int MAX_SIZE = 100;

D. int max_size = 100;

Solution

1. Step 1: Identify constant declaration rules

   Constants should be declared with final and use uppercase letters with underscores.

2. Step 2: Evaluate each option

   final int MAX_SIZE = 100; uses final and uppercase naming, matching best practices.

3. Final Answer:

   final int MAX_SIZE = 100; -> Option C

4. Quick Check:

   Constants use final + uppercase = final int MAX_SIZE = 100; [OK]

Hint: Constants use final and uppercase names [OK]

Common Mistakes:

• Not using final keyword for constants
• Using lowercase or camelCase for constant names
• Missing underscores in multi-word constants

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

public class Test {
    public static void main(String[] args) {
        int x = 5;
        int y = 10;
        int sum = x + y;
        System.out.println("Sum is: " + sum);
    }
}

medium

A. Sum is: 510

B. Sum is: 15

C. Sum is: x + y

D. Compilation error

Solution

1. Step 1: Understand variable values and addition

   Variables x and y hold 5 and 10, sum is their addition: 5 + 10 = 15.

2. Step 2: Check output statement

   Prints "Sum is: " concatenated with sum value 15.

3. Final Answer:

   Sum is: 15 -> Option B

4. Quick Check:

   5 + 10 = 15 output = Sum is: 15 [OK]

Hint: Add numbers before printing to avoid string concatenation errors [OK]

Common Mistakes:

• Concatenating numbers as strings without addition
• Confusing variable names with strings
• Syntax errors from missing semicolons

4. Identify the best fix for the following Java code snippet that lacks proper indentation and comments:

public class Example {
public static void main(String[] args) {
int a=10;int b=20;int c=a+b;System.out.println(c);
}
}

medium

A. Add indentation and comments explaining variables

B. Remove all spaces to make code compact

C. Change variable names to single letters

D. Delete the print statement

Solution

1. Step 1: Recognize code readability issues

   Code is hard to read due to no indentation and no comments.

2. Step 2: Apply best practices

   Adding indentation and comments improves clarity and maintainability.

3. Final Answer:

   Add indentation and comments explaining variables -> Option A

4. Quick Check:

   Indentation + comments = Add indentation and comments explaining variables [OK]

Hint: Indent code blocks and add comments for clarity [OK]

Common Mistakes:

• Making code compact by removing spaces
• Using unclear variable names
• Removing useful print statements

5. You have a Java program that uses the number 3.14159 multiple times for calculations. What is the best practice to improve this code?

hard

A. Use a variable named piValue without final keyword

B. Keep using the number 3.14159 directly everywhere

C. Write the number as a string and convert it each time

D. Replace all occurrences with a constant named PI declared as final double PI = 3.14159;

Solution

1. Step 1: Identify magic number usage

   Repeated use of 3.14159 is a magic number and reduces clarity.

2. Step 2: Use a named constant

   Declaring final double PI = 3.14159; improves readability and maintainability.

3. Final Answer:

   Replace all occurrences with a constant named PI declared as final double PI = 3.14159; -> Option D

4. Quick Check:

   Use constants for magic numbers = Replace all occurrences with a constant named PI declared as final double PI = 3.14159; [OK]

Hint: Use final constants for repeated fixed values [OK]

Common Mistakes:

• Using magic numbers directly
• Using non-final variables for constants
• Converting numbers from strings repeatedly