Null detection

Cleaning Data in Java

Dennis Lee

Software Engineer

Where is the data?

Missing data: nulls and blanks
- Nulls: Data not available
- Blanks: Whitespaces, likely errors

Title	Publish Date	Rating	Review Count	Price
Python Crash Course	1/10/23	4.8	165	$30.61
	9/13/19	4.8	2,521	$38.00
Clean Code	8/1/08	[null]	[null]	[null]

Errors from null values

// book is missing reviewCount, rating, and price
BookSales book = new BookSales("Clean Code", LocalDate.of(2008, 8, 1),
                               null, null, null)


// rating is null, so the code will throw a NullPointerException
int rating = book.rating();

Exception in thread "main" java.lang.NullPointerException

Checking for null values

// Import Objects
import java.util.Objects;

// Use .isNull()
if (Objects.isNull(book.rating())) {
    System.out.println("Missing rating");
}

Missing rating

Providing default values for nulls

import java.util.Optional;

// Use Optional.ofNullable for numbers
double rating = Optional.ofNullable(book.rating()).orElse(0.0);
System.out.println("Book rating: " + rating);

Book rating: 0.0

// Use Objects.toString for strings
String displayTitle = Objects.toString(book.title(), "[No Title]");
System.out.println(displayTitle);

Book title: [No Title]

Checking for blank/null strings

import org.apache.commons.lang3.StringUtils;  // Utility for string operations

// book is missing a title
BookSales book = new BookSales(" ", LocalDate.of(2019, 9, 13), 2521, 4.5, 38.00)


if StringUtils.isBlank(book.title()) {
    System.out.println("Invalid - empty title"); 
}

Invalid - empty title

Checking for blank numbers

// priceText is blank
String priceText = " ";

// Check for blank values before converting to a number
if StringUtils.isBlank(priceText) {
    System.out.println("Invalid price: blank detected");
}

Invalid price: blank detected

Summary: detecting nulls and blanks

Null values indicate missing or undefined data
- Key imports: java.util.Objects and java.util.Optional
- Prevent NullPointerException by checking nulls before use
- Use Objects.isNull() to check for nulls
- Use Optional.ofNullable() to provide defaults
Blank values indicate empty or whitespace-only text
- Key import: org.apache.commons.lang3.StringUtils
- Use StringUtils.isBlank() to detect "", null, or whitespace
- Common in data entry errors

Let's practice!

Cleaning Data in Java