Introduction

Necessity IT industry operates in such a diverse environment that software programs should not be confined to a single PC. Rather, they should move from a single user environment to mainframes, to networks, to network of networks, and so on. A giant program can be developed which integrates numerous mini programs which were developed by geographically distributed programmers, and all of them can be connected online. Such a distributed programming techniques and environments are no longer a dream but a reality, and it is Java, the Internet programming language, which makes it possible.

Scope Java was developed by Sun Microsystems Inc. with the intent to create a dynamic, object-oriented programming (OOP) language, suitable for using the same types of development tasks as C and C++, but without the difficulties and bugs common to those languages. This is why Java has been touted as “a better C++”; it contains all the essential OOP features, but with lower complexities than C++. Sun describes Java as a “simple, object-oriented, distributed, interpreted, robust, secure, architecture neutral, portable, high-performance, multithreaded, and dynamic language.”

Your learning In this chapter we shall briefly highlight the various features of Java programming, its superiority over other programming languages, and the tools available for its programming. At the end, you will be able to run your first program in Java.

Concept of Programming

Application systems Computer programming is used to build a software system (e.g., Microsoft Word, Library Information System, Internet Explorer browser, mobile app, printer’s driver software, to name a few). These software systems take an input and then produce an output (Figure 1.1).

Introduction

Language elements At this point, we are assuming that you have successfully installed Java and were able to run the sample programs given in Chapter 1. It is time now to start programming. As a Java programmer, it is necessary to have full understanding of the elements of the language like keywords, literals, data types, operators, loops, branches, etc.

Strongly typed language Java programming language mostly follows syntax similar to that of C/ C++ to write statements and expressions. So if you are familiar with C/ C++, it will be easy for you to understand Java. As with all modern programming languages like C/ C++, Java is a strongly typed language, which means all data to be used should be defined their types in programs. Java supports several types of data, which are called primitive data types. In this chapter we will examine several data types, their structures, operations on them, and how they can be utilized to solve problems. Constants and variables are the two basic programming elements. It is necessary to learn how the variables of different data types can be defined. Java has a very good composition of defining arrays of elements of different types, which is also an interesting concept to learn. You may use different data types to declare variables and to create arrays of elements.

Introduction

From design to coding The separation of “designing” from “coding” was one of the most fundamental advances in programming style in the recent past, and object-oriented languages are capable of implementing a strong form of this separation. According to this programming paradigm, you design the classes first and decide the relationships between these classes, and then you implement the Java code needed for each of the methods in your class design. The advantages with this style is that, you can change your mind about aspects of the design without affecting anything but small, local pieces of your programs; vice-versa, you can change the implementation of any method without affecting the design.

To achieve this, the Java developer includes two very innovative features: package and interface. Packages provide class repositories, grouping them together, and controlling their access to the outside world. Interfaces provide a way of grouping abstract method definitions and sharing them among classes.

Your learning This chapter plans to discuss the package and interface concepts in Java. You will learn how to design, use, and create your own packages and interfaces. The specific topics which you will learn include: a detailed discussion of designing classes and coding classes; what are packages and why they are useful for designing classes; using other available packages in your own classes; how you can create your own packages; what interfaces you can utilize in terms of code reuse and design; designing and working with interfaces; and many more.

Introduction

Why multithreading? Multitasking is a very common features in today’s computation environment. Java supports thread-based approach to multi-tasking, which is more precisely called multithreading. Multithreading means multiple flow of control. Multithreading programming is a conceptual paradigm for programming where one can divide a program into two or more processes which can be run in parallel. There are two main advantages of multithreading: First, a program with multiple threads will, in general, result in better utilization of system resources, including the CPU, because another line of execution can use the CPU when one line of execution is idle or blocked. Second, there are several problems which are solved better by multiple threads. For example, we can easily write a multithreaded program to show animation, play music, display documents, and download files from the network, etc., all of them at the same time.

Heavyweight versus lightweight programming Multitasking involves complex processing that an execution environment has to perform while it executes the program. If processes are heavyweight tasks, they require their own separate address spaces. The inter-process communication becomes expensive and reduces the advantages of the concurrent execution. Context switching from one process to another is also costly. Java follows the concept of threads and thus the concept of thread-based multitasking. All the threads are lightweights, which share the same address space. Hence interthread communication remains inexpensive and context switching from one thread to the next is at a lower cost.

Introduction

Why inheritance? Class is the basic element of any software in object-oriented system design approach. In the last chapter, you have learned about how to write classes in Java programs. In software development, a software is under constant updation, for example, extension (from one version to the next or from one release to another, etc.), or modification (correction of some faults or to make it compatible with new technology, hardware, etc.). The requirement is that all the development should take place without disturbing the existing system and, of course, with minimum effort and time.

Your learning Inheritance in Java is a clever mechanism to support these requirements. It allows an efficient and secure way to share code, modify it, and reuse it. With the help of inheritance, you will learn how to extend a given class and thus access its fields and methods. You will also learn how to hide some fields and methods from a parent class to the extended class.

Concept of Inheritance

Basic concept The inheritance concept is related to taxonomy or classification. For example, Figure 4.1 shows taxonomy (in partial form) of animals. It looks like a tree (this is why it is also called and inheritance tree). This tree bears the information that lion and hyena, for example, have some common characteristics. In addition, they have their own characteristics.

Introduction

Real-world programming requirements In the previous chapters, you have studied a little about input and output related methods in Java. Chapter 2 mentioned input to programs and output from programs considering the programs are simple and text-based (reading from keyboard), and writing output on the console (display). However, in many real world applications, input–output are more versatile: inputs are from many different sources (such as files, other programs, network channels, etc.); similarly, outputs from a program may go into several destinations like files, external programs, network lines in web, etc. (Figure 8.1).

Java’s key to success While a majority of programming languages are keyboard–console input and output (IO), Java is much ahead of them, supporting efficient, strong, and flexible real-world programming with networking, files, and many more options. Java includes the java.io package which contains nearly every class you might ever need to perform IO. As a unique concept, Java introduced stream for flow of different forms of data to-and-fro the sources and destinations. There are numerous classes representing different streams for input sources and output destinations. The streams in the java.io package support many kinds of data such as primitives, object, localized characters, etc.

The java.io package is vast. It defines over seventy classes and interfaces, many of which have a large number of methods. Covering all of them in detail is beyond the scope of this book and often it is not necessary for a programmer to know about them.

Welcome to the wonderful world of Java programming and thank you for your interest in this book. We would like to share some thoughts behind writing this book.

Background

With the growth of Information and Communication Technology (ICT), there is a need to develop large and complex software. To meet this requirement, object-oriented programming paradigms are popular among software professionals. The software is required to be platform independent, Internet enabled, easy to modify and update, secure, and robust. To cater to all these requirements, Java programming language appears to be the most suitable object-oriented programming language as it meets all these requirements. Java was developed by Sun Microsystems in 1995 and has emerged as the best programming environment according to the Time magazine. Today, Java is used for mobile programming, Internet programming, software development, and for numerous other applications in distributed systems and commercial hardware products. This book aims to cover the essential features of Java programming so that software professionals can improve their skills to cope with the current demands of the IT industry. In addition, this book can help students and faculty members to learn the programming language with the minimum effort and solve many problems in their fields.

Why This Book?

The need: Java is vast. Unlike other programming languages, Java is constantly evolving. The latest version, Java 14 or JDK 14, was released on March 17, 2020. With every new release, many features are deprecated and many new features are added. Developers keep on adding new features so that the programming language can meet the changing needs of the software industry. Thus Java has become vast, with a large number of features. However, this is at the cost of increasing the difficulty in learning the language. It is not easy for programmers to grasp the numerous syntaxes and semantics that the language contains in its present form. As experienced teachers of Computer Science and Engineering, we know how to modulate a discussion so that learners can grasp the concepts with minimum cognitive load. The learners need to feel they have the competence to learn and start loving the language. In our opinion, existing books fail to do so. Hence the need of a new book like this.

Introduction

What is the issue? Programmers in any language endeavor to write bug-free programs, programs that never crash, programs that can handle any situation efficiently, and that can recover from unusual situations without causing the users any undue inconvenience. Good intentions aside, programs that cover all these points don’t exist. In real life, errors occur, either because the programmer didn’t anticipate every situation the code would get into (or did not have the time to test the programs enough), or because of situations outside the programmer’s control like bad data from users, corrupt files that do not have the right data in them, network connections that do not connect, hardware devices that do not respond, to name a few.

Requirement In Java, unusual events that may cause a program to fail are called exceptions. The dictionary meaning of “exception” is “an abnormal situation.” What will happen to the program if an abnormal situation occurs? For example, what result will your calculations return when divide x by y when y = 0? Or, if you want to store a value in the array in its 100th location while the size of the array is 50? In practice, in such a situation, your execution will be suspended immediately, for which you are not really prepared.