String truncation to determine whether the string is equal or not and whether the string is null. Java, Android

String truncation to determine whether the string is equal or not and whether the string is null. Java, Android

Recently, when I was working on the Android project, I encountered a string truncation problem. I also knew whether the string is equal or not and whether the string is null. So I sorted it out and used it later, for your reference, can I share some better or other methods? Thank you!

1. The subSequence method can be used to intercept characters of any length.

For example:

String s = "AndroidandJava" System. out. println (s. subSequence (0, 1); the running result is: A. The original method is String. subSequence (beginIndex (number of starting bytes), endIndex (number of ending bytes ))

Ii. judge whether the strings are equal

Public class Test {public static void main (String [] args) {String a = "abcdef"; String B = "bcdef"; if (! A. equals (B) {System. out. print ("a is not equal to B");} else {System. out. print ("a equals B") ;}} the running result is: a is not equal to B

Note: Generally, equals is used to compare objects or strings, and = is used to compare values.

3. Four methods to determine whether a string is null:

Method 1: Compare the string length with high efficiency. It is the best method I know:

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

Method 2: The method is intuitive and convenient, but the efficiency is very low:

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

Method 3: the method provided by Java SE 6.0 is almost the same as method 2. But for compatibility consideration, method 2 is recommended.

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

Method 4: this is a simple and intuitive method with high efficiency, which is similar to method 2 and method 3:

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

Note: s = null is necessary.

If the String type is null and the equals (String) or length () operation is performed, java. lang. NullPointerException is thrown.

And the s = null sequence must appear in the front, otherwise java. lang. NullPointerException will also be thrown.

The following Java code:

String str = null; if (str. equals ("") | str = null) {// an exception is thrown. System. out. println ("success ");}//"". equals (str); Make sure that no null error is returned.

You can give us some suggestions. Thank you!