Classes & fields in Java

State made private, behavior made public.

var book = new Book("Dune", 412);
book.addPages(20);
System.out.println(book.describe());

class Book {
    private final String title;
    private int pages;

    Book(String title, int pages) {
        this.title = title;
        this.pages = pages;
    }

    void addPages(int more) { pages += more; }

    String describe() { return title + ", " + pages + " pages"; }
}

How it works

1. private final fields set once in the constructor.
2. this.title = title tells the parameter and field apart.
3. Methods like addPages are the only door to the state.

Keywords and builtins used here

• Book
• addPages
• class
• describe
• final
• int
• new
• private
• return
• this
• var
• void

The run, in numbers

Lines

17

Characters to type

334

Tokens

100

Three-star pace

90 tpm

At the three-star pace of 90 tokens a minute, this run takes about 67 seconds.

Type this snippet

Step 1 of 4 in Classes & records, step 18 of 29 in Language basics.

← Previous Next →