Java's StringUtil.isEmpty(str) and "".equals(str) are both methods used to determine whether a string is empty, but they have some different usage scenarios.

 StringUtil.isEmpty()

  StringUtil.isEmpty(str) is usually used to determine whether the string is null or the length is 0, if the string is null or the length is 0, it returns true, otherwise it returns false. This method is suitable for situations where it is necessary to determine whether multiple strings are empty, and can avoid null pointer exceptions .

 "".equals()

  "".equals(str) is used to determine whether the string is an empty string (that is, the length is 0). If the string is an empty string, it returns true, otherwise it returns false. This method is suitable for situations where it is only necessary to determine whether a string is an empty string.

  If you need to determine whether multiple strings are empty at the same time, it is recommended to use StringUtil.isEmpty(str). If you only need to judge whether a string is empty, it is recommended to use "".equals(str). In this way, a more appropriate method can be selected according to the actual situation, and the readability and efficiency of the code can be improved.

Determine whether multiple strings are empty at the same time

public static boolean isAllEmpty(String... strs) {
    for (String str : strs) {
        if (StringUtil.isNotEmpty(str)) {
            return false;
        }
    }
    return true;
}

 In this method, we use variable parameters to receive multiple strings, and then loop through these strings. As long as one of the strings is not empty, it returns false, indicating that not all are empty. Otherwise, return true after the loop ends, indicating that all strings are empty.

  It should be noted that when judging whether it is empty, the StringUtil.isNotEmpty(str) method is used instead of the StringUtil.isEmpty(str) method. This is because when judging whether multiple strings are all empty, if you use the StringUtil.isEmpty(str) method, as long as one string is null or empty, it will return true, and you will not judge other strings Is it empty. Therefore, it is more accurate to use the StringUtil.isNotEmpty(str) method, which returns true only when the string is not null and the length is not 0, which can avoid misjudgment.

  Using this method can easily determine whether multiple strings are empty, avoiding repeated codes, and can improve the readability of the code.

  When we need to determine whether multiple strings are all empty, we can use variable parameters to receive these strings. For example:

String str1 = "";
String str2 = null;
String str3 = "hello";
boolean result = isAllEmpty(str1, str2, str3);
System.out.println(result); // output false

  In this example, we define three strings str1, str2, and str3, where str1 is an empty string, str2 is null, and str3 is not empty. Then we call the isAllEmpty method to determine whether the three strings are all empty. Since str3 is not empty, false will be returned when looping through str3, indicating that not all are empty.

  If we set str3 to null or an empty string, then the loop traverses to the end and does not find that any string is not empty, and finally returns true, indicating that all strings are empty. For example:

String str1 = "";
String str2 = null;
String str3 = "";
boolean result = isAllEmpty(str1, str2, str3);
System.out.println(result); // output true

 In this example, we set both str1 and str2 to null or empty strings, only str3 is also empty, so the isAllEmpty method will return true after the loop ends, indicating that all strings are empty.

  When we need to determine whether a string is null or the length is 0, we can use the StringUtil.isEmpty(str) method. For example:

String str = "";
if (StringUtil. isEmpty(str)) {
     System.out.println("The string is empty");
} else {
     System.out.println("The string is not empty");
}

 In this example, we define an empty string str, and then use the StringUtil.isEmpty(str) method to determine whether the string is empty. Since the length of the string is 0, the StringUtil.isEmpty(str) method returns true, indicating that the string is empty. Depending on the return value, we can perform different logic.

Another example:

String str = null;
if (StringUtil. isEmpty(str)) {
     System.out.println("The string is empty");
} else {
     System.out.println("The string is not empty");
}

 In this example, we set the string str to null, and the StringUtil.isEmpty(str) method will also return true, indicating that the string is empty. This method can avoid null pointer exceptions, because when the StringUtil.isEmpty(str) method is executed, even if the string is null, a null pointer exception will not be thrown.

  It should be noted that this method is only suitable for judging whether a single string is empty. If you need to judge whether multiple strings are empty, you need to use variable parameters to judge. For details, please refer to the above example .

  When the StringUtil.isEmpty(str) method is used, even if the string is null, a null pointer exception will not be thrown. When does a null pointer exception occur?

  A null pointer exception usually occurs when a variable or object with a null value is used in the program. For example:

String str = null;
int length = str.length(); // throws a null pointer exception

  In this example, we define a string str and set it to null. Then we use the str.length() method to get the length of the string, and a null pointer exception will be thrown at this time, because when we use the method of the str object, we are actually using the method of an empty object.

another example:

String[] strs = {"hello", "world", null};
for (String str : strs) {
     int length = str.length(); // throws a null pointer exception
}

 In this example, we define a string array strs where the third element is null. We then iterate through the array using a for loop and use the str.length() method on each string to get its length. Since the third element is null, a null pointer exception is thrown.

  It should be noted that although the StringUtil.isEmpty(str) method can avoid null pointer exceptions, in some cases, we may need to determine whether the string is null. At this time, you can use str == null to judge. For example:

String str = null;
if (str == null) {
     System.out.println("The string is null");
} else if (StringUtil. isEmpty(str)) {
     System.out.println("The string is empty");
} else {
     System.out.println("The string is not empty");
}

 In this example, we first use str == null to determine whether the string is null, and if it is null, output "the string is null"; otherwise, use the StringUtil.isEmpty(str) method to determine whether the string is empty . This avoids null pointer exceptions and handles string null and string empty cases separately.

  Note that "".equals(str) should not be written as str.equals(""), otherwise, when str is null, a null pointer exception will be reported.

Two judgments, which one has better performance?

  From a performance point of view, using StringUtil.isEmpty() will perform slightly better. This is because when judging whether a string is empty, the StringUtil.isEmpty() method only needs to make one judgment, while using the "".equals() method requires two judgments, one is to judge whether the string is null, The other time is to judge whether the length of the string is 0.

  Although the gap is not big, using StringUtil.isEmpty() can slightly improve performance in scenarios where a large number of strings are judged. But it should be noted that this performance difference is negligible. In actual development, more attention should be paid to the readability and maintainability of the code.

Two judgments, which one is better for readability and ease of maintenance

  From the point of view of readability and ease of maintenance, it is better to use StringUtil.isEmpty() because the meaning of this method is clearer. Using the "".equals() method can also achieve the same effect, but it needs to write more code to make a judgment. It is more concise and clear to directly call a special tool class method.

  In addition, if you need to modify the judgment conditions later, you only need to modify it in the tool class method, but you need to modify it in multiple places when using the "".equals() method, which increases the difficulty of code maintenance. Therefore, in terms of readability and ease of maintenance, using StringUtil.isEmpty() is superior.