How to determine whether a Java string is empty?

Java method to determine whether a string is empty

Method 1: The most popular method, intuitive, convenient, but very efficient Low:

if(s == null || s.equals(""))

Method 2: Compare string lengths, high efficiency, the best method I know:

if(s == null || s.length() == 0)

length is an attribute, a property owned by a general collection class object, to obtain the collection the size of.

For example: array.length is to get the length of the array.

length() is a method. Generally, string class objects have this method, which also obtains the length of the string. [Recommended learning: java course]

For example: String.length();

Method 3: Only available in Java SE 6.0 Method, the efficiency is almost the same as method two, but for compatibility reasons, it is recommended to use method two.

if(s == null || s.isEmpty())

Method four: This is a more intuitive and simple method, and the efficiency is also very high, compared with The efficiency of methods two and three is almost the same:

if (s == null || s == "")

Note: s == null is necessary.

If the String type is null, perform equals( String) or length() operations will throw java.lang.NullPointerException.

And the order of s==null must appear first, otherwise java.lang.NullPointerException will also be thrown.

The difference between Java empty string and null:

1. Type

null represents the value of an object, not a character string. For example, when declaring a reference to an object, String a = null;
"" represents an empty string, which means its length is 0. For example, declare a string String str = "" ;

2. Memory allocation

String str = null; means declaring a string object The reference, but the pointer is null, which means that it does not point to any memory space;

String str = ""; means declaring a reference of string type, its value is " "Empty string, this str reference points to the memory space of the empty string;

In Java, variables and reference variables are stored in the stack (stack), and objects (generated by new) are stored in In the heap:

is as follows:

String str = new String("abc") ;

ps: = The one on the left is stored in the stack (stack), = The one on the right is stored in the heap (heap).

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