Check if a String is empty or null in Java

This post will discuss how to check if a string is empty or null in Java. Note that a string is empty if and only if its length is 0.

1. Using `String.isEmpty()` method

From Java 7 onward, the recommended approach is to use the String.isEmpty() method to check for an empty string in Java. To avoid NullPointerException if the string is null, a null check should precede the method call.

class Main

{

public static void main(String[] args)

{

String str = "";

System.out.println(str == null || str.isEmpty()); // true

}

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2. Using `String.length()` method

The isEmpty() method internally calls to the length() method of the String class. In Java 6 and less, since the isEmpty() method is not available, we can directly call the length() method, as shown below:

class Main

{

public static void main(String[] args)

{

String str = "";

System.out.println(str == null || str.length() == 0); // true

}

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3. Using `String.equals()` method

One can also use the String.equals() method to do an equality check against an empty string.

class Main

{

private static String EMPTY = "";

public static void main(String[] args)

{

String str = "";

System.out.println(str == null || str.equals(EMPTY)); // true

System.out.println(str == null || EMPTY.equals(str)); // true

}

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4. Using Guava Library

Guava’s Strings class has static utility method isNullOrEmpty(String), which returns true if the given string is null or is the empty string.

import com.google.common.base.Strings;

class Main

{

public static void main(String[] args)

{

System.out.println(Strings.isNullOrEmpty("")); // true

System.out.println(Strings.isNullOrEmpty(null)); // true

System.out.println(Strings.isNullOrEmpty("Java")); // false

}

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5. Using Apache Commons Lang

Apache Commons Lang library provides StringUtils.isEmpty(String), which checks if a string is an empty string or null. It also provides the StringUtils.isBlank(String) method, which also checks for whitespace.

import org.apache.commons.lang3.StringUtils;

class Main

{

public static void main(String[] args)

{

System.out.println(StringUtils.isEmpty("")); // true

System.out.println(StringUtils.isEmpty(null)); // true

System.out.println(StringUtils.isEmpty("Java")); // false

System.out.println(StringUtils.isBlank(" ")); // true

}

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That’s all about determining whether a String is empty or null in Java.

Check if a String is empty or null in Java

1. Using String.isEmpty() method

2. Using String.length() method

3. Using String.equals() method

4. Using Guava Library

5. Using Apache Commons Lang

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1. Using `String.isEmpty()` method

2. Using `String.length()` method

3. Using `String.equals()` method