The History and Evolution of Java

The History and Evolution of Java

To fully understand Java, one must understand the reasons behind its creation, the forces that shaped it,

and the legacy that it inherits. Like the successful computer languages that came before, Java is a blend of

the best elements of its rich heritage combined with the innovative concepts required by its unique mission.

While the remaining chapters of this book describe the practical aspects of Java—including its syntax, key

libraries, and applications—this chapter explains how and why Java came about, what makes it so important,

and how it has evolved over the years.

Although Java has become inseparably linked with the online environment of the Internet, it is important

to remember that Java is first and foremost a programming language. Computer language innovation

and development occurs for two fundamental reasons:

• To adapt to changing environments and uses

• To implement refinements and improvements in the art of programming

As you will see, the development of Java was driven by both elements in nearly equal measure.

Java’s Lineage

Java is related to C++, which is a direct descendant of C. Much of the character of Java is inherited from

these two languages. From C, Java derives its syntax. Many of Java’s object-oriented features were influenced

by C++. In fact, several of Java’s defining characteristics come from—or are responses to—its predecessors.

Moreover, the creation of Java was deeply rooted in the process of refinement and adaptation that

has been occurring in computer programming languages for the past several decades. For these reasons,

this section reviews the sequence of events and forces that led to Java. As you will see, each innovation in

language design was driven by the need to solve a fundamental problem that the preceding languages could

not solve. Java is no exception.

The Birth of Modern Programming: C

The C language shook the computer world. Its impact should not be underestimated, because it fundamentally

changed the way programming was approached and thought about. The creation of C was a direct

result of the need for a structured, efficient, high-level language that could replace assembly code when

creating systems programs. As you probably know, when a computer language is designed, trade-offs are

often made, such as the following:

• Ease-of-use versus power

• Safety versus efficiency

• Rigidity versus extensibility

Prior to C, programmers usually had to choose between languages that optimized one set of traits or the

other. For example, although FORTRAN could be used to write fairly efficient programs for scientific applications,

it was not very good for system code. And while BASIC was easy to learn, it wasn’t very powerful,

and its lack of structure made its usefulness questionable for large programs. Assembly language can be

used to produce highly efficient programs, but it is not easy to learn or use effectively. Further, debugging

assembly code can be quite difficult.

Another compounding problem was that early computer languages such as BASIC, COBOL, and

FORTRAN were not designed around structured principles. Instead, they relied upon the GOTO as a primary

means of program control. As a result, programs written using these languages tended to produce “spaghetti

code”—a mass of tangled jumps and conditional branches that make a program virtually impossible

to understand. While languages like Pascal are structured, they were not designed for efficiency, and failed

to include certain features necessary to make them applicable to a wide range of programs. (Specifically,

given the standard dialects of Pascal available at the time, it was not practical to consider using Pascal for

systems-level code.)

So, just prior to the invention of C, no one language had reconciled the conflicting attributes that had

dogged earlier efforts. Yet the need for such a language was pressing. By the early 1970s, the computer

revolution was beginning to take hold, and the demand for software was rapidly outpacing programmers’

ability to produce it. A great deal of effort was being expended in academic circles in an attempt to create

a better computer language. But, and perhaps most importantly, a secondary force was beginning to be

felt. Computer hardware was finally becoming common enough that a critical mass was being reached. No

longer were computers kept behind locked doors. For the first time, programmers were gaining virtually

unlimited access to their machines. This allowed the freedom to experiment. It also allowed programmers

to begin to create their own tools. On the eve of C’s creation, the stage was set for a quantum leap forward

in computer languages.

Invented and first implemented by Dennis Ritchie on a DEC PDP-11 running the UNIX operating system,

C was the result of a development process that started with an older language called BCPL, developed by

Martin Richards. BCPL influenced a language called B, invented by Ken Thompson, which led to the development

of C in the 1970s. For many years, the de facto standard for C was the one supplied with the UNIX

operating system and described in The C Programming Language by Brian Kernighan and Dennis Ritchie

(Prentice-Hall, 1978). C was formally standardized in December 1989, when the American National Standards

Institute (ANSI) standard for C was adopted.

The creation of C is considered by many to have marked the beginning of the modern age of computer

languages. It successfully synthesized the conflicting attributes that had so troubled earlier languages. The

result was a powerful, efficient, structured language that was relatively easy to learn. It also included one

other, nearly intangible aspect: it was a programmer’s language. Prior to the invention of C, computer languages

were generally designed either as academic exercises or by bureaucratic committees. C is different.

It was designed, implemented, and developed by real, working programmers, reflecting the way that they

approached the job of programming. Its features were honed, tested, thought about, and rethought by the

people who actually used the language. The result was a language that programmers liked to use. Indeed,

C quickly attracted many followers who had a near-religious zeal for it. As such, it found wide and rapid

acceptance in the programmer community. In short, C is a language designed by and for programmers. As

you will see, Java inherited this legacy.

C++: The Next Step

During the late 1970s and early 1980s, C became the dominant computer programming language, and it is

still widely used today. Since C is a successful and useful language, you might ask why a need for something

else existed. The answer is complexity. Throughout the history of programming, the increasing complexity of

programs has driven the need for better ways to manage that complexity. C++ is a response to that need.

To better understand why managing program complexity is fundamental to the creation of C++, consider

the following.

Approaches to programming have changed dramatically since the invention of the computer. For example,

when computers were first invented, programming was done by manually toggling in the binary machine

instructions by use of the front panel. As long as programs were just a few hundred instructions long,

this approach worked. As programs grew, assembly language was invented so that a programmer could deal

with larger, increasingly complex programs by using symbolic representations of the machine instructions.

As programs continued to grow, high-level languages were introduced that gave the programmer more tools

with which to handle complexity.

The first widespread language was, of course, FORTRAN. While FORTRAN was an impressive first step,

it is hardly a language that encourages clear and easy-to-understand programs. The 1960s gave birth to

structured programming. This is the method of programming championed by languages such as C. The use

of structured languages enabled programmers to write, for the first time, moderately complex programs

fairly easily. However, even with structured programming methods, once a project reaches a certain size,

its complexity exceeds what a programmer can manage. By the early 1980s, many projects were pushing

the structured approach past its limits. To solve this problem, a new way to program was invented, called

object-oriented programming (OOP). Object-oriented programming is discussed in detail later in this book,

but here is a brief definition: OOP is a programming methodology that helps organize complex programs

through the use of inheritance, encapsulation, and polymorphism.

In the final analysis, although C is one of the world’s great programming languages, there is a limit to its

ability to handle complexity. Once the size of a program exceeds a certain point, it becomes so complex that

it is difficult to grasp as a totality. While the precise size at which this occurs differs, depending upon both

the nature of the program and the programmer, there is always a threshold at which a program becomes

unmanageable. C++ added features that enabled this threshold to be broken, allowing programmers to

comprehend and manage larger programs.

C++ was invented by Bjarne Stroustrup in 1979, while he was working at Bell Laboratories in Murray

Hill, New Jersey. Stroustrup initially called the new language “C with Classes.” However, in 1983, the name

was changed to C++. C++ extends C by adding object-oriented features. Because C++ is built on the

foundation of C, it includes all of C’s features, attributes, and benefits. This is a crucial reason for the success

of C++ as a language. The invention of C++ was not an attempt to create a completely new programming

language. Instead, it was an enhancement to an already highly successful one.

The Stage Is Set for Java

By the end of the 1980s and the early 1990s, object-oriented programming using C++ took hold. Indeed,

for a brief moment it seemed as if programmers had finally found the perfect language. Because C++ blended

the high efficiency and stylistic elements of C with the object-oriented paradigm, it was a language that

could be used to create a wide range of programs. However, just as in the past, forces were brewing that

would, once again, drive computer language evolution forward. Within a few years, the World Wide Web

and the Internet would reach critical mass. This event would precipitate another revolution in programming.

The Creation of Java

Java was conceived by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and Mike Sheridan at Sun

Microsystems, Inc. in 1991. It took 18 months to develop the first working version. This language was initially

called “Oak,” but was renamed “Java” in 1995. Between the initial implementation of Oak in the fall

of 1992 and the public announcement of Java in the spring of 1995, many more people contributed to the

design and evolution of the language. Bill Joy, Arthur van Hoff, Jonathan Payne, Frank Yellin, and Tim

Lindholm were key contributors to the maturing of the original prototype.

Somewhat surprisingly, the original impetus for Java was not the Internet! Instead, the primary motivation

was the need for a platform-independent (that is, architecture-neutral) language that could be used to

create software to be embedded in various consumer electronic devices, such as microwave ovens and remote

controls. As you can probably guess, many different types of CPUs are used as controllers. The trouble

with C and C++ (and most other languages) is that they are designed to be compiled for a specific target.

Although it is possible to compile a C++ program for just about any type of CPU, to do so requires a full

C++ compiler targeted for that CPU. The problem is that compilers are expensive and time-consuming

to create. An easier—and more cost-efficient—solution was needed. In an attempt to find such a solution,

Gosling and others began work on a portable, platform-independent language that could be used to produce

code that would run on a variety of CPUs under differing environments. This effort ultimately led to the

creation of Java.

About the time that the details of Java were being worked out, a second, and ultimately more important,

factor was emerging that would play a crucial role in the future of Java. This second force was, of course,

the World Wide Web. Had the Web not taken shape at about the same time that Java was being implemented,

Java might have remained a useful but obscure language for programming consumer electronics.

However, with the emergence of the World Wide Web, Java was propelled to the forefront of computer

language design, because the Web, too, demanded portable programs.

Most programmers learn early in their careers that portable programs are as elusive as they are desirable.

While the quest for a way to create efficient, portable (platform-independent) programs is nearly as

old as the discipline of programming itself, it had taken a back seat to other, more pressing problems. Further,

because (at that time) much of the computer world had divided itself into the three competing camps

of Intel, Macintosh, and UNIX, most programmers stayed within their fortified boundaries, and the urgent

need for portable code was reduced. However, with the advent of the Internet and the Web, the old problem

of portability returned with a vengeance. After all, the Internet consists of a diverse, distributed universe

populated with various types of computers, operating systems, and CPUs. Even though many kinds of platforms

are attached to the Internet, users would like them all to be able to run the same program. What was

once an irritating but low-priority problem had become a high-profile necessity.

By 1993, it became obvious to members of the Java design team that the problems of portability frequently

encountered when creating code for embedded controllers are also found when attempting to create

code for the Internet. In fact, the same problem that Java was initially designed to solve on a small scale

could also be applied to the Internet on a large scale. This realization caused the focus of Java to switch

from consumer electronics to Internet programming. So, while the desire for an architecture-neutral programming

language provided the initial spark, the Internet ultimately led to Java’s large-scale success.

As mentioned earlier, Java derives much of its character from C and C++. This is by intent. The Java

designers knew that using the familiar syntax of C and echoing the object-oriented features of C++ would

make their language appealing to the legions of experienced C/C++ programmers. In addition to the surface

similarities, Java shares some of the other attributes that helped make C and C++ successful. First,

Java was designed, tested, and refined by real, working programmers. It is a language grounded in the

needs and experiences of the people who devised it. Thus, Java is a programmer’s language. Second, Java is

cohesive and logically consistent. Third, except for those constraints imposed by the Internet environment,

Java gives you, the programmer, full control. If you program well, your programs reflect it. If you program

poorly, your programs reflect that, too. Put differently, Java is not a language with training wheels. It is a

language for professional programmers.

Because of the similarities between Java and C++, it is tempting to think of Java as simply the “Internet

version of C++.” However, to do so would be a large mistake. Java has significant practical and

philosophical differences. While it is true that Java was influenced by C++, it is not an enhanced version

of C++. For example, Java is neither upwardly nor downwardly compatible with C++. Of course, the

similarities with C++ are significant, and if you are a C++ programmer, then you will feel right at home

with Java. One other point: Java was not designed to replace C++. Java was designed to solve a certain

set of problems. C++ was designed to solve a different set of problems. Both will coexist for many years

to come.

As mentioned at the start of this chapter, computer languages evolve for two reasons: to adapt to

changes in environment and to implement advances in the art of programming. The environmental change

that prompted Java was the need for platform-independent programs destined for distribution on the Internet.

However, Java also embodies changes in the way that people approach the writing of programs. For

example, Java enhanced and refined the object-oriented paradigm used by C++, added integrated support

for multithreading, and provided a library that simplified Internet access. In the final analysis, though, it

was not the individual features of Java that made it so remarkable. Rather, it was the language as a whole.

Java was the perfect response to the demands of the then newly emerging, highly distributed computing

universe. Java was to Internet programming what C was to system programming: a revolutionary force that

changed the world.

The C# Connection

The reach and power of Java continues to be felt in the world of computer language development. Many

of its innovative features, constructs, and concepts have become part of the baseline for any new language.

The success of Java is simply too important to ignore.

Perhaps the most important example of Java’s influence is C#. Created by Microsoft to support the .NET

Framework, C# is closely related to Java. For example, both share the same general syntax, support distributed

programming, and utilize the same object model. There are, of course, differences between Java and

C#, but the overall “look and feel” of these languages is very similar. This “cross-pollination” from Java

to C# is the strongest testimonial to date that Java redefined the way we think about and use a computer

language.

How Java Changed the Internet

The Internet helped catapult Java to the forefront of programming, and Java, in turn, had a profound effect

on the Internet. In addition to simplifying web programming in general, Java innovated a new type of networked

program called the applet that changed the way the online world thought about content. Java also

addressed some of the thorniest issues associated with the Internet: portability and security. Let’s look more

closely at each of these.

Java Applets

An applet is a special kind of Java program that is designed to be transmitted over the Internet and automatically

executed by a Java-compatible web browser. Furthermore, an applet is downloaded on demand,

without further interaction with the user. If the user clicks a link that contains an applet, the applet will

be automatically downloaded and run in the browser. Applets are intended to be small programs. They are

typically used to display data provided by the server, handle user input, or provide simple functions, such

as a loan calculator, that execute locally, rather than on the server. In essence, the applet allows some functionality

to be moved from the server to the client.

The creation of the applet changed Internet programming because it expanded the universe of objects

that can move about freely in cyberspace. In general, there are two very broad categories of objects that are

transmitted between the server and the client: passive information and dynamic, active programs. For example,

when you read your e-mail, you are viewing passive data. Even when you download a program, the

program’s code is still only passive data until you execute it. By contrast, the applet is a dynamic, self-executing

program. Such a program is an active agent on the client computer, yet it is initiated by the server.

As desirable as dynamic, networked programs are, they also present serious problems in the areas of

security and portability. Obviously, a program that downloads and executes automatically on the client

computer must be prevented from doing harm. It must also be able to run in a variety of different environments

and under different operating systems. As you will see, Java solved these problems in an effective

and elegant way. Let’s look a bit more closely at each.

Security

As you are likely aware, every time you download a “normal” program, you are taking a risk, because the

code you are downloading might contain a virus, Trojan horse, or other harmful code. At the core of the

problem is the fact that malicious code can cause its damage because it has gained unauthorized access to

system resources. For example, a virus program might gather private information, such as credit card numbers,

bank account balances, and passwords, by searching the contents of your computer’s local file system.

In order for Java to enable applets to be downloaded and executed on the client computer safely, it was

necessary to prevent an applet from launching such an attack.

Java achieved this protection by confining an applet to the Java execution environment and not allowing

it access to other parts of the computer. (You will see how this is accomplished shortly.) The ability

to download applets with confidence that no harm will be done and that no security will be breached is

considered by many to be the single most innovative aspect of Java.

Portability

Portability is a major aspect of the Internet because there are many different types of computers and operating

systems connected to it. If a Java program were to be run on virtually any computer connected to the

Internet, there needed to be some way to enable that program to execute on different systems. For example,

in the case of an applet, the same applet must be able to be downloaded and executed by the wide variety

of CPUs, operating systems, and browsers connected to the Internet. It is not practical to have different

versions of the applet for different computers. The same code must work on all computers. Therefore, some

means of generating portable executable code was needed. As you will soon see, the same mechanism that

helps ensure security also helps create portability.

Java’s Magic: The Bytecode

The key that allows Java to solve both the security and the portability problems just described is that the

output of a Java compiler is not executable code. Rather, it is bytecode. Bytecode is a highly optimized set of

instructions designed to be executed by the Java run-time system, which is called the Java Virtual Machine

(JVM). In essence, the original JVM was designed as an interpreter for bytecode. This may come as a bit of

a surprise since many modern languages are designed to be compiled into executable code because of performance

concerns. However, the fact that a Java program is executed by the JVM helps solve the major

problems associated with web-based programs. Here is why.

Translating a Java program into bytecode makes it much easier to run a program in a wide variety of

environments because only the JVM needs to be implemented for each platform. Once the run-time package

exists for a given system, any Java program can run on it. Remember, although the details of the JVM will

differ from platform to platform, all understand the same Java bytecode. If a Java program were compiled

to native code, then different versions of the same program would have to exist for each type of CPU connected

to the Internet. This is, of course, not a feasible solution. Thus, the execution of bytecode by the JVM

is the easiest way to create truly portable programs.

The fact that a Java program is executed by the JVM also helps to make it secure. Because the JVM is

in control, it can contain the program and prevent it from generating side effects outside of the system. As

you will see, safety is also enhanced by certain restrictions that exist in the Java language.

In general, when a program is compiled to an intermediate form and then interpreted by a virtual machine,

it runs slower than it would run if compiled to executable code. However, with Java, the differential

between the two is not so great. Because bytecode has been highly optimized, the use of bytecode enables

the JVM to execute programs much faster than you might expect.

Although Java was designed as an interpreted language, there is nothing about Java that prevents onthe-

fly compilation of bytecode into native code in order to boost performance. For this reason, the HotSpot

technology was introduced not long after Java’s initial release. HotSpot provides a Just-In-Time (JIT) compiler

for bytecode. When a JIT compiler is part of the JVM, selected portions of bytecode are compiled into

executable code in real time, on a piece-by-piece, demand basis. It is important to understand that it is not

practical to compile an entire Java program into executable code all at once, because Java performs various

run-time checks that can be done only at run time. Instead, a JIT compiler compiles code as it is needed,

during execution. Furthermore, not all sequences of bytecode are compiled—only those that will benefit

from compilation. The remaining code is simply interpreted. However, the just-in-time approach still yields

a significant performance boost. Even when dynamic compilation is applied to bytecode, the portability and

safety features still apply, because the JVM is still in charge of the execution environment.

Servlets: Java on the Server Side

As useful as applets can be, they are just one half of the client/server equation. Not long after the initial

release of Java, it became obvious that Java would also be useful on the server side. The result was the

servlet. A servlet is a small program that executes on the server. Just as applets dynamically extend the functionality

of a web browser, servlets dynamically extend the functionality of a web server. Thus, with the

advent of the servlet, Java spanned both sides of the client/server connection.

Servlets are used to create dynamically generated content that is then served to the client. For example,

an online store might use a servlet to look up the price for an item in a database. The price information is

then used to dynamically generate a web page that is sent to the browser. Although dynamically generated

content is available through mechanisms such as CGI (Common Gateway Interface), the servlet offers several

advantages, including increased performance.

Because servlets (like all Java programs) are compiled into bytecode and executed by the JVM, they are

highly portable. Thus, the same servlet can be used in a variety of different server environments. The only

requirements are that the server support the JVM and a servlet container.

The Java Buzzwords

No discussion of Java’s history is complete without a look at the Java buzzwords. Although the fundamental

forces that necessitated the invention of Java are portability and security, other factors also played an important

role in molding the final form of the language. The key considerations were summed up by the Java

team in the following list of buzzwords:

• Simple

• Secure

• Portable

• Object-oriented

• Robust

• Multithreaded

• Architecture-neutral

• Interpreted

• High performance

• Distributed

• Dynamic

Two of these buzzwords have already been discussed: secure and portable. Let’s examine what each of

the others implies.

Simple

Java was designed to be easy for the professional programmer to learn and use effectively. Assuming that

you have some programming experience, you will not find Java hard to master. If you already understand

the basic concepts of object-oriented programming, learning Java will be even easier. Best of all, if you are

an experienced C++ programmer, moving to Java will require very little effort. Because Java inherits the

C/C++ syntax and many of the object-oriented features of C++, most programmers have little trouble

learning Java.

Object-Oriented

Although influenced by its predecessors, Java was not designed to be source-code compatible with any

other language. This allowed the Java team the freedom to design with a blank slate. One outcome of this

was a clean, usable, pragmatic approach to objects. Borrowing liberally from many seminal object-software

environments of the last few decades, Java manages to strike a balance between the purist’s “everything is

an object” paradigm and the pragmatist’s “stay out of my way” model. The object model in Java is simple

and easy to extend, while primitive types, such as integers, are kept as high-performance nonobjects.

Robust

The multiplatformed environment of the Web places extraordinary demands on a program, because the program

must execute reliably in a variety of systems. Thus, the ability to create robust programs was given a

high priority in the design of Java. To gain reliability, Java restricts you in a few key areas to force you to

find your mistakes early in program development. At the same time, Java frees you from having to worry

about many of the most common causes of programming errors. Because Java is a strictly typed language, it

checks your code at compile time. However, it also checks your code at run time. Many hard-to-track-down

bugs that often turn up in hard-to-reproduce run-time situations are simply impossible to create in Java.

Knowing that what you have written will behave in a predictable way under diverse conditions is a key

feature of Java.

To better understand how Java is robust, consider two of the main reasons for program failure: memory

management mistakes and mishandled exceptional conditions (that is, run-time errors). Memory management

can be a difficult, tedious task in traditional programming environments. For example, in C/C++,

the programmer must manually allocate and free all dynamic memory. This sometimes leads to problems,

because programmers will either forget to free memory that has been previously allocated or, worse, try

to free some memory that another part of their code is still using. Java virtually eliminates these problems

by managing memory allocation and deallocation for you. (In fact, deallocation is completely automatic,

because Java provides garbage collection for unused objects.) Exceptional conditions in traditional environments

often arise in situations such as division by zero or “file not found,” and they must be managed with

clumsy and hard-to-read constructs. Java helps in this area by providing object-oriented exception handling.

In a well-written Java program, all run-time errors can—and should—be managed by your program.

Multithreaded

Java was designed to meet the real-world requirement of creating interactive, networked programs. To

accomplish this, Java supports multithreaded programming, which allows you to write programs that do

many things simultaneously. The Java run-time system comes with an elegant yet sophisticated solution

for multiprocess synchronization that enables you to construct smoothly running interactive systems. Java’s

easy-to-use approach to multithreading allows you to think about the specific behavior of your program,

not the multitasking subsystem.

Architecture-Neutral

A central issue for the Java designers was that of code longevity and portability. At the time of Java’s creation,

one of the main problems facing programmers was that no guarantee existed that if you wrote a

program today, it would run tomorrow—even on the same machine. Operating system upgrades, processor

upgrades, and changes in core system resources can all combine to make a program malfunction. The Java

designers made several hard decisions in the Java language and the Java Virtual Machine in an attempt to

alter this situation. Their goal was “write once; run anywhere, any time, forever.” To a great extent, this

goal was accomplished.

Interpreted and High Performance

As described earlier, Java enables the creation of cross-platform programs by compiling into an intermediate

representation called Java bytecode. This code can be executed on any system that implements the

Java Virtual Machine. Most previous attempts at cross-platform solutions have done so at the expense of

performance. As explained earlier, the Java bytecode was carefully designed so that it would be easy to

translate directly into native machine code for very high performance by using a just-in-time compiler. Java

run-time systems that provide this feature lose none of the benefits of the platform-independent code.

Distributed

Java is designed for the distributed environment of the Internet because it handles TCP/IP protocols. In

fact, accessing a resource using a URL is not much different from accessing a file. Java also supports Remote

Method Invocation (RMI). This feature enables a program to invoke methods across a network.

Dynamic

Java programs carry with them substantial amounts of run-time type information that is used to verify and

resolve accesses to objects at run time. This makes it possible to dynamically link code in a safe and expedient

manner. This is crucial to the robustness of the Java environment, in which small fragments of bytecode

may be dynamically updated on a running system.

The Evolution of Java

The initial release of Java was nothing short of revolutionary, but it did not mark the end of Java’s era of

rapid innovation. Unlike most other software systems that usually settle into a pattern of small, incremental

improvements, Java continued to evolve at an explosive pace. Soon after the release of Java 1.0, the designers

of Java had already created Java 1.1. The features added by Java 1.1 were more significant and

substantial than the increase in the minor revision number would have you think. Java 1.1 added many new

library elements, redefined the way events are handled, and reconfigured many features of the 1.0 library.

It also deprecated (rendered obsolete) several features originally defined by Java 1.0. Thus, Java 1.1 both

added to and subtracted from attributes of its original specification.

The next major release of Java was Java 2, where the “2” indicates “second generation.” The creation

of Java 2 was a watershed event, marking the beginning of Java’s “modern age.” The first release of Java 2

carried the version number 1.2. It may seem odd that the first release of Java 2 used the 1.2 version number.

The reason is that it originally referred to the internal version number of the Java libraries, but then

was generalized to refer to the entire release. With Java 2, Sun repackaged the Java product as J2SE (Java

2 Platform Standard Edition), and the version numbers began to be applied to that product.

Java 2 added support for a number of new features, such as Swing and the Collections Framework, and

it enhanced the Java Virtual Machine and various programming tools. Java 2 also contained a few deprecations.

The most important affected the Thread class in which the methods suspend( ), resume( ), and

stop( ) were deprecated.

J2SE 1.3 was the first major upgrade to the original Java 2 release. For the most part, it added to existing

functionality and “tightened up” the development environment. In general, programs written for version

1.2 and those written for version 1.3 are source-code compatible. Although version 1.3 contained a smaller

set of changes than the preceding three major releases, it was nevertheless important.

The release of J2SE 1.4 further enhanced Java. This release contained several important upgrades,

enhancements, and additions. For example, it added the new keyword assert, chained exceptions, and

a channel-based I/O subsystem. It also made changes to the Collections Framework and the networking

classes. In addition, numerous small changes were made throughout. Despite the significant number of new

features, version 1.4 maintained nearly 100 percent source-code compatibility with prior versions.

The next release of Java was J2SE 5, and it was revolutionary. Unlike most of the previous Java upgrades,

which offered important, but measured improvements, J2SE 5 fundamentally expanded the scope,

power, and range of the language. To grasp the magnitude of the changes that J2SE 5 made to Java, consider

the following list of its major new features:

• Generics

• Annotations

• Autoboxing and auto-unboxing

• Enumerations

• Enhanced, for-each style for loop

• Variable-length arguments (varargs)

• Static import

• Formatted I/O

• Concurrency utilities

This is not a list of minor tweaks or incremental upgrades. Each item in the list represented a significant addition

to the Java language. Some, such as generics, the enhanced for, and varargs, introduced new syntax

elements. Others, such as autoboxing and auto-unboxing, altered the semantics of the language. Annotations

added an entirely new dimension to programming. In all cases, the impact of these additions went

beyond their direct effects. They changed the very character of Java itself.

The importance of these new features is reflected in the use of the version number “5.” The next version

number for Java would normally have been 1.5. However, the new features were so significant that a shift

from 1.4 to 1.5 just didn’t seem to express the magnitude of the change. Instead, Sun elected to increase the

version number to 5 as a way of emphasizing that a major event was taking place. Thus, it was named J2SE

5, and the Developer’s Kit was called JDK 5. However, in order to maintain consistency, Sun decided to use

1.5 as its internal version number, which is also referred to as the developer version number. The “5” in J2SE

5 is called the product version number.

The next release of Java was called Java SE 6. Sun once again decided to change the name of the Java

platform. First, notice that the “2” was dropped. Thus, the platform was now named Java SE, and the official

product name was Java Platform, Standard Edition 6. The Java Developer’s Kit was called JDK 6. As

with J2SE 5, the 6 in Java SE 6 is the product version number. The internal, developer version number is

1.6.

Java SE 6 built on the base of J2SE 5, adding incremental improvements. Java SE 6 added no major

features to the Java language proper, but it did enhance the API libraries, added several new packages, and

offered improvements to the runtime. It also went through several updates during its (in Java terms) long

life cycle, with several upgrades added along the way. In general, Java SE 6 served to further solidify the

advances made by J2SE 5.

Java SE 7

The newest release of Java is called Java SE 7, with the Java Developer’s Kit being called JDK 7, and an

internal version number of 1.7. Java SE 7 is the first major release of Java since Sun Microsystems was acquired

by Oracle (a process that began in April 2009 and that was completed in January 2010). Java SE 7

contains many new features, including significant additions to the language and the API libraries. Upgrades

to the Java run-time system that support non-Java languages are also included, but it is the language and

library additions that are of most interest to Java programmers.

The new language features were developed as part of Project Coin. The purpose of Project Coin was to

identify a number of small changes to the Java language that would be incorporated into JDK 7. Although

these new features are collectively referred to as “small,” the effects of these changes are quite large in

terms of the code they impact. In fact, for many programmers, these changes may well be the most important

new features in Java SE 7. Here is a list of the new language features:

• A String can now control a switch statement.

• Binary integer literals.

• Underscores in numeric literals.

• An expanded try statement, called try-with-resources, that supports automatic resource management.

(For example, streams can now be closed automatically when they are no longer needed.)

• Type inference (via the diamond operator) when constructing a generic instance.

• Enhanced exception handling in which two or more exceptions can be caught by a single catch (multicatch)

and better type checking for exceptions that are rethrown.

• Although not a syntax change, the compiler warnings associated with some types of varargs methods

have been improved, and you have more control over the warnings.

As you can see, even though the Project Coin features were considered small changes to the language,

their benefits will be much larger than the qualifier “small” would suggest. In particular, the try-with-resources

statement will profoundly affect the way that stream-based code is written. Also, the ability to now

use a String to control a switch statement is a long-desired improvement that will simplify coding in many

situations.

Java SE 7 makes several additions to the Java API library. Two of the most important are the enhancements

to the NIO Framework and the addition of the Fork/Join Framework. NIO (which originally stood for

New I/O) was added to Java in version 1.4. However, the changes proposed for Java SE 7 fundamentally

expand its capabilities. So significant are the changes, that the term NIO.2 is often used.

The Fork/Join Framework provides important support for parallel programming. Parallel programming

is the name commonly given to the techniques that make effective use of computers that contain more

than one processor, including multicore systems. The advantage that multicore environments offer is the

prospect of significantly increased program performance. The Fork/Join Framework addresses parallel programming

by

• Simplifying the creation and use of tasks that can execute concurrently

• Automatically making use of multiple processors

Therefore, by using the Fork/Join Framework, you can easily create scaleable applications that automatically

take advantage of the processors available in the execution environment. Of course, not all algorithms

lend themselves to parallelization, but for those that do, a significant improvement in execution

speed can be obtained.

The material in this book has been updated to reflect Java SE 7, with many new features, updates, and

additions indicated throughout.

A Culture of Innovation

Since the beginning, Java has been at the center of a culture of innovation. Its original release redefined

programming for the Internet. The Java Virtual Machine (JVM) and bytecode changed the way we think

about security and portability. The applet (and then the servlet) made the Web come alive. The Java Community

Process (JCP) redefined the way that new ideas are assimilated into the language. Because Java is

used for Android programming, Java is part of the smartphone revolution. The world of Java has never

stood still for very long. Java SE 7 is the latest release in Java’s ongoing, dynamic history.