SUBSTR alternate in apex

Another alternative for Substr in apex is as follows:

You can use a combination of Right and Substring method to achieve the desired output in Apex. Below code for your reference.

        String str = 'SLA-UPsdfdsfdsfG-4HR-4ON'; String res = str.right(7).substring(0, 3); System.debug('res is::'+res);

The result would be 4HR for the above code. What is salesforce string class ?

The salesforce String class represents character strings. All string literals in Java programs, such as "abc" , are implemented as instances of this class. Strings are constant; their values cannot be changed after they are created. ... Because String objects are immutable they can be shared.