Java method to determine if a string is not empty

A string or string (String) is a string of characters composed of numbers, letters, and underscores. Generally recorded as s=“a1a2···an” (n>=0). It is a data type that represents text in programming languages.

1. The methods to determine whether a string str is empty are:

1. str!=null;

2. "".equals(str);

3. str.length()!=0;

Explanation:

1. null means that this string does not point to anything. If you call it at this time method, then a null pointer exception will occur.

2. "" means that it points to a string with a length of 0, and it is safe to call its method at this time.

3. null is not an object, "" is an object, so null has not allocated space, "" has allocated space, for example:

String str1 = null; str引用为空 
String str2 = ""; str应用一个空串

str1 is not an instantiated object yet, str2 has been Instantiate.

Objects are compared using equals, and null is compared using the equal sign.

If str1=null; the following writing is wrong:

if(str1.equals("")||str1==null){ }

The correct writing is

if(str1==null||str1.equals("")){ //先判断是不是对象，如果是，再判断是不是空字符串 }

4. Therefore, to determine whether a string is empty, first Just make sure it's not null, and then judge its length.

String str = xxx;
if(str != null && str.length() != 0) { }

For more java knowledge, please pay attention to the java basic tutorial column.

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