Core Java APIs

This chapter explains many core data structures in Java, along with the most common Application Programming Interface (APIs) to access them. For example, String and StringBuilder, along with their associated APIs, are used to create and manipulate text data. An array, List, Set, or Map are used to manage often large groups of data. Once a String object is created, it is not allowed to change. It cannot be made larger or smaller, and you cannot change one of the characters inside it. You can think of a String as a storage box you have perfectly full and whose sides can't bulge. There's no way to add objects, nor can you replace objects without disturbing the entire arrangement. The trade‐off for the optimal packing is zero flexibility. Mutable is another word for changeable. Immutable is the opposite‐an object that can't be changed once it's created. On the exam, you need to know that String is immutable.