In Java the StringUtils tool class resolves the judgment that String is null

The criterion for determining whether a string is null is str==null or str.length ()==0

1. The following is an example of StringUtils judging whether it is empty:

　　StringUtils.isEmpty(null) = true
　　StringUtils.isEmpty("") = true
　　StringUtils.isEmpty(" ") = false // Note that in  StringUtils  The space in is treated as non-null 
　　StringUtils.isEmpty("  ") = false
　　StringUtils.isEmpty("bob") = false
　　StringUtils.isEmpty(" bob ") = false

2. public static boolean isNotEmpty(String str)

Determines whether a string is non-null, equal to! isEmpty(String str)

Here is an example:

StringUtils.isNotEmpty(null) = false
　　StringUtils.isNotEmpty("") = false
　　StringUtils.isNotEmpty(" ") = true
　　StringUtils.isNotEmpty("     ") = true
　　StringUtils.isNotEmpty("bob") = true
　　StringUtils.isNotEmpty(" bob ") = true

3. public static boolean isBlank(String str)

Determines whether a string is null or has a length of 0 or consists of a blank character (whitespace)

Here is an example:

StringUtils.isBlank(null) = true
　　StringUtils.isBlank("") = true
　　StringUtils.isBlank(" ") = true
　　StringUtils.isBlank("    ") = true
　　StringUtils.isBlank("\t \n \f \r") = true  // For tabs, line feeds, page breaks, and carriage returns 
　　StringUtils.isBlank()  // Recognition is a blank character 
　　StringUtils.isBlank("\b") = false  //"\b" Is the word boundary character 
　　StringUtils.isBlank("bob") = false
　　StringUtils.isBlank(" bob ") = false

4. public static boolean isNotBlank(String str)

Determines whether a string is not null and has a length of 0 and is not formed by a blank character (whitespace), equal to! isBlank(String str)

Here is an example:

StringUtils.isNotBlank(null) = false
　　StringUtils.isNotBlank("") = false
　　StringUtils.isNotBlank(" ") = false
　　StringUtils.isNotBlank("     ") = false
　　StringUtils.isNotBlank("\t \n \f \r") = false
　　StringUtils.isNotBlank("\b") = true
　　StringUtils.isNotBlank("bob") = true
　　StringUtils.isNotBlank(" bob ") = true

conclusion

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