The String class belongs to the java.lang package. This is the default package of the Java language therefore it is not mandatory to import it to use its classes.

In Java immutable objects are those whose data can’t be changed or modified (once modified). String class is immutable i.e. once we create a String object its data cannot be modified.

Create a REST service hosted on a server and place java method inside it. Now you can call this REST service from a SAPUI5 application using AJAX by passing required parameters.