How to use if statement in java to determine whether a string is empty or null

First of all, distinguish between empty string and null string

1. The empty string "" is a string with a length of 0. It has its own string length (0) and Content (empty), method to determine if a string is empty:

if (str.length() == 0);

or

if (str.equals(""));

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2. The null string means that there is currently no object associated with the variable. The method to check whether a string is null:

 if (str == null);

3. To check that a string is neither a null string nor an empty string, use the following methods. Judgment:

if (str != null && str.length() != 0);

Note: First check that str is not null, otherwise an error will occur when adjusting the length() method on a null value.

4. Use the StringUtils tool class to determine whether it is neither null nor empty, as follows:

if (StringUtils.isNotBlank(str))

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