Cay S. Horstmann - Core Java for the Impatient, 3rd Edition

In this chapter, you will learn about the basic data types and control structures of the Java language. I assume that you are an experienced programmer in some other language and that you are familiar with concepts such as variables, loops, function calls, and arrays, but perhaps with a different syntax. This chapter will get you up to speed on the Java way. I will also give you some tips on the most useful parts of the Java API for manipulating common data types.

The key points of this chapter are:

1. In Java, all methods are declared in a class. You invoke a nonstatic method on an object of the class to which the method belongs.

2. Static methods are not invoked on objects. Program execution starts with the static main method.

3. Java has eight primitive types: four signed integral types, two floating-point types, char, and boolean.

4. The Java operators and control structures are very similar to those of C or JavaScript.

5. There are four forms of switch: expressions and statements with and without fall through.

6. The Math class provides common mathematical functions.

7. String objects are sequences of characters or, more precisely, Unicode code points in the UTF-16 encoding.

8. Use the text box syntax to declare multiline string literals.

9. With the System.out object, you can display output in a terminal window. A Scanner tied to System.in lets you read terminal input.

10. Arrays and collections can be used to collect elements of the same type.

When learning any new programming language, it is traditional to start with a program that displays the message Hello, World!. That is what we will do in the following sections.

Without further ado, here is the Hello, World program in Java.

package ch01.sec01;// Our first Java programpublic class HelloWorld { public static void main(String[] args) { System.out.println("Hello, World!"); }}

Lets examine this program:

Java is an object-oriented language. In your program, you manipulate (mostly) objects by having them do work. Each object that you manipulate belongs to a specific class, and we say that the object is an instance of that class. A class defines what an objects state can be and and what it can do. In Java, all code is defined inside classes. We will look at objects and classes in detail in . This program is made up of a single class HelloWorld.

main is a method, that is, a function declared inside a class. The main method is the first method that is called when the program runs. It is declared as static to indicate that the method does not operate on any objects. (When main gets called, there are only a handful of predefined objects, and none of them are instances of the HelloWorld class.) The method is declared as void to indicate that it does not return any value. See for the meaning of the parameter declaration String[] args.

In Java, you can declare many features as public or private, and there are a couple of other visibility levels as well. Here, we declare the HelloWorld class and the main method as public, which is the most common arrangement for classes and methods.

A package is a set of related classes. It is a good idea to place each class in a package so you can group related classes together and avoid conflicts when multiple classes have the same name. In this book, well use chapter and section numbers as package names. The full name of our class is ch01.sec01.HelloWorld. has more to say about packages and package naming conventions.

The line starting with // is a comment. All characters between // and the end of the line are ignored by the compiler and are meant for human readers only.