Java 8 – Check if a String is Empty or Null

Introduction

In Java 8, checking if a string is null or empty is a common task when dealing with user inputs or data from external sources. Ensuring that a string is not null or empty is important to avoid NullPointerException or unintended behaviors in your program. Java provides several ways to check this condition, and you can simplify the process using utility classes or even the Stream API.

In this guide, we will learn how to check if a string is null or empty in Java 8.

Solution Steps

1. Use == to Check for Null: First, check if the string is null using the == operator.
2. Use isEmpty() to Check for Empty String: If the string is not null, use the isEmpty() method to check if it contains no characters.
3. Use Optional.ofNullable() (Optional): You can use Optional to handle null checks more elegantly.
4. Combine Checks: Combine both checks (null and empty) in a single condition.

Java Program

Method 1: Check for null and Empty String Using == and isEmpty()

public class CheckStringEmptyOrNull {
    public static void main(String[] args) {
        // Step 1: Define some sample strings
        String str1 = null;
        String str2 = "";
        String str3 = "Hello, World!";

        // Step 2: Check if each string is null or empty
        System.out.println(isNullOrEmpty(str1));  // true
        System.out.println(isNullOrEmpty(str2));  // true
        System.out.println(isNullOrEmpty(str3));  // false
    }

    // Method to check if a string is null or empty
    public static boolean isNullOrEmpty(String str) {
        return str == null || str.isEmpty();
    }
}

Output

true
true
false

Explanation

Step 1: Define Sample Strings

We define three sample strings:

• str1 is null,
• str2 is an empty string "",
• str3 contains a value "Hello, World!".

Step 2: Check if Each String is null or Empty

We check each string using a method isNullOrEmpty() that combines a null check with an isEmpty() check:

public static boolean isNullOrEmpty(String str) {
    return str == null || str.isEmpty();
}

If the string is null or empty, the method returns true; otherwise, it returns false.

Method 2: Using Optional.ofNullable() (Java 8)

In Java 8, you can use the Optional class to make your null checks more concise and avoid potential NullPointerException.

import java.util.Optional;

public class CheckStringUsingOptional {
    public static void main(String[] args) {
        // Step 1: Define some sample strings
        String str1 = null;
        String str2 = "";
        String str3 = "Hello, World!";

        // Step 2: Check if each string is null or empty using Optional
        System.out.println(isNullOrEmptyUsingOptional(str1));  // true
        System.out.println(isNullOrEmptyUsingOptional(str2));  // true
        System.out.println(isNullOrEmptyUsingOptional(str3));  // false
    }

    // Method to check if a string is null or empty using Optional
    public static boolean isNullOrEmptyUsingOptional(String str) {
        return Optional.ofNullable(str).map(String::isEmpty).orElse(true);
    }
}

Output

true
true
false

Explanation

Step 1: Define Sample Strings

The same sample strings (str1, str2, and str3) are used as in Method 1.

Step 2: Check If Each String is null or Empty Using Optional

We use Optional.ofNullable() to wrap the string, and then map() the isEmpty() check. If the string is null, the orElse(true) will return true. If the string is non-null, it will evaluate the isEmpty() method:

public static boolean isNullOrEmptyUsingOptional(String str) {
    return Optional.ofNullable(str).map(String::isEmpty).orElse(true);
}

Conclusion

In Java 8, you can easily check if a string is null or empty using either a combination of == and isEmpty() or by leveraging the Optional class for a more elegant solution. Both approaches are effective, and you can choose based on your preferred coding style or project requirements.