CoreJavaSE9fortheImpatien

Preface

Java is now over twenty years old, and the classic book, Core .Java, covers,in meticulous detail, not just the language but all core libraries and a multitude of changes between versions, spanning two volumes and well over 2,000 pages. However, ifyou just want to be productive with modern Java, there is a much faster. easier pathway for learning the language and core libraries. In this book, I don't retrace history and don't dwell on features of past versions.I show you the good parts ofJava as it exists today,with Java 9,so you can put your knowledge to work quickly.

As with my previous "Impatient" books, I quickly cut to the chase, showing you what you need to know to solve a programming problem without lecturing about the superiority of one paradigm over another.I also present the information in small chunks, organized so that you can quickly retrieve it when needed.

Assuming you are proficient in some other programming language,such as C++, JavaScript, Objective C, PHP, or Ruby, with this book you will learn how to become a competent Java programmer. Icover all aspects of Java that a developer needs to know,including the powerful concepts oflambda expressions and streams.I tell you where to find out more about old-fashioned concepts that you might still see in legacy code, but I don't dwell on them.

A key reason to use Java is to tackle concurrent programming. With parallel algorithms and threadsafe data structures readily available in the Java library, the way application programmers should handle concurrent programming has completely changed. I provide fresh coverage,showing you how to use the powerful library features instead of error-prone low-level constructs.

Traditionally, books on Java have focused on user interface programming—but nowadays, few developers produce user interfaces on desktop computers. If you intend to use Java for server-side programming or Android programming, vou wil be able to use this book effectively without being distracted by desktop GUI code. Finally, this book is written for application programmers, not for a college course and not for systems wizards. The book covers issues that application programmers need to wrestle with,such as logging and working with files—but you won't learn how to implement a linked list by hand or how to write a web server.

I hope you enjoy this rapid-fire introduction into modern Java, and I hope it will make your work with Java productive and enjoyable.

Chapter 1. Fundamental Programming Structures

Topics in This Chapter-

1.1Our First Program

■1.2 Primitive Types

1.3-Variables

1.4 Arithmetic Operations-

1.5 Srings

■1.6 Input and Output

■1.7 Control Flo

■1.8 Arrays and Array Lists

1.9 Functional Decomposition

■Exercise

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 vou 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. Youinvoke 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. The Math class provides common mathematical functions.

6.String objects are sequences of characters or, more precisely, Unicode code

points in the UTF-16 encoding.

7. With the System.out object,you can display output in a terminal window.A

Scanner tied to System.in lets you read terminal input.

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

1.1 Our First Program

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.

1.1.1 Dissecting the"Hello, World"Program Without further ado,here is the "Hello, World"program in Java. Click here to view code image

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

Let's 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 object's 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 Chapter2. 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 Section1.8.8."Command-Line Arguments"(page 49)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 ofrelated 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 isch01.sec01.HelloWorld. Chapter2 has more to say about packages and package naming conventions.

·The line starting with // is acomment. All characters between // and the end o the line are ignored by the compiler and are meant for human readers only.●Finally, we come to the body of the main method. In our example,it consists of single line with a command to print a message to System.out,an object representing the "standard output"of the Java program.

As you can see, Java is not a scripting language that can be used to quickly dash off a few commands. It is squarely intended as a language for larger programs that benefit from being organized into classes, packages,and modules. (Modules are introduced in Chapter 15.)

Java is also quite simple and uniform. Some languages have global variables and functions as well as variables and methods inside classes. In Java, everything is declared inside a class. This uniformity can lead to somewhat verbose code, but it makes it easy to understand the meaning of a program.

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