Best practices in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a constant for the maximum number of users.

Java

public class Config {
    public static final int MAX_USERS = [1];
}

Drag options to blanks, or click blank then click option'

Afinal

B"100"

CmaxUsers

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around numbers which makes them strings.

Trying to use variable names instead of values.

Constants in Java are declared using public static final and assigned a fixed value like 100.

2fill in blank

medium

Complete the method to override the toString method properly.

Java

public class Person {
    private String name;
    @Override
    public String toString() {
        return [1];
    }
}

Drag options to blanks, or click blank then click option'

A"Person: " + name

Bname

Cname.toString()

Dsuper.toString()

Attempts:

3 left

💡 Hint

Common Mistakes

Returning just the variable without context.

Calling toString() on a String variable unnecessarily.

Overriding toString() should return a meaningful string, like "Person: " plus the name.

3fill in blank

hard

Fix the error in the method to properly close the resource using try-with-resources.

Java

public void readFile(String path) {
    try (BufferedReader reader = new BufferedReader(new FileReader([1]))) {
        System.out.println(reader.readLine());
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Drag options to blanks, or click blank then click option'

AfilePath

B"path"

Cpath

Dreader

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string literal instead of the variable.

Using an undefined variable name.

The variable path is passed as the filename to FileReader. Using the string "path" would look for a file literally named 'path'.

4fill in blank

hard

Fill both blanks to create a for-each loop that prints each element in the list.

Java

List<String> items = List.of("apple", "banana", "cherry");
for ([1] : [2]) {
    System.out.println(item);
}

Drag options to blanks, or click blank then click option'

AString item

Bitems

Cint i

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using an index variable instead of the element variable.

Using the wrong collection variable name.

A for-each loop uses the syntax: for (Type variable : collection). Here, String item and items are correct.

5fill in blank

hard

Fill all three blanks to create a map comprehension that filters and transforms entries.

Java

Map<String, Integer> result = data.entrySet().stream()
    .filter(e -> e.getValue() [1] [2])
    .collect(Collectors.toMap(
        e -> e.getKey().toUpperCase(),
        e -> e.getValue() [3] 2
    ));

Drag options to blanks, or click blank then click option'

A>

B10

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong comparison operator.

Using addition instead of multiplication for transformation.

This code filters entries with values greater than 10, then collects them into a map with uppercase keys and values multiplied by 2.

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