Assuming you know that the String age
is a valid number (if you don’t know it is a valid number you will have to add some code to check for this).
You can simply convert age
using Integer.parseInt then add the int 10
and the convert the result back to a String using String.valueOf:
String age = "14";
age = String.valueOf(Integer.parseInt(age) + 10);
System.out.println(age); // 24