2. Software Engineering and Java

Software Engineering:

The term software engineering has frequently been used for what this course introduces, but this term is simultaneously falling on hard times in some circles while it becomes deeply entrenched in others.

Knowing something of the history of software engineering helps understand the conflict here. As software systems grew in the 1960's and 1970's, people looking at the economics of software noticed something disturbing: While the price of hardware was falling, following Moore's Law, the cost of software was soaring. This came to be known as the "software crisis" and it never ended. There were huge software boondoggles in both government and private industry. F. P. Brooks' classic book The Mythical Man Month (1975, Addison-Wesley, and still in print) documented the problem and proposed some solutions.

Many observers of this situation found the contrast between the productivity of hardware engineering and the crisis with software development asked: "Why can't software development be done as an engineering discipline." This led naturally to the term "software engineering" as a buzzword for how software ought to be developed.

The negative assessment of software engineering rests on two observations: First, many of the early proponents of software engineering seem to have had romantic misunderstandings of the nature of engineering. If you ask the designers of a bridge across a large river what they are doing, they will typically describe the initial stages of the design as being high art. Selecting between a cable-stayed bridge and an arch bridge, for example. And then, a typical civil engineer would say, "and then the real engineering begins, deciding how much rebar to put where, how many bolts go in this joint, how thick is that cable?" The work the civil engineer describes as "real engineering" is comparable to the detail work in computing that people sometimes call "coding".

Meanwhile, the work that proponents of software engineering want to call engineering and want to systematize seems comparable to the high level design work that civil engineers might refer to as being a high art.

Second, the industrial response to the emergence of the term "software engineering" was the immediate promotion of this term to a job title. This allowed parallel pay and promotion structures programmers and conventional engineers without offending personnell managers.

Now, 35 years after the emergence of software engineering, there are skeptics in both the academic and industrial world who consider software engineering to be, at best "computer science lite" (to quote one former department chair).

Meanwhile the study of software engineering has produced insights into the management of large projects. Some things that sound like buzzwords that have come from software engineering are actually valueable. "Extreme programming" is an example. While slavish adherence to the XP methodology may be silly, the underlying ideas of incremental development are very powerful. UML, as a formal graphical language for describing programs may be foolish, but selective informal use of the notation is frequently useful during the early stages of a software project.

Origins of Object Oriented Programming:

The idea of object-oriented programming was born in two different domains, independently and around the same time in the mid 1960s:

• Discrete event simulation. One of the first computer applicaitons where hugely complex programs became important was discrete-event simulation. In a discrete event model, the world is described in terms of a sequence of events. Each event takes place at an instant of time, and each event:
  • may change some aspect of the state of the world, and
  • may schedule future events.

  Viewing the world this way is a gross oversimplificaiton, but nonetheless, discrete event models have proven to be extremely applicable to areas as far apart as digital logic and logistics. The problem with discrete event models is that there are a huge number of different classes of events and classes of objects in a typical model. Making sense of these was a problem.

  Consider a traffic simulation model: The primary classes are roads, vehicles and intersections. Vehicles come in many subclasses, cars, trucks and vans, for example, with trucks subdivided into semi-trailer trucks and simple trucks.

• Operating systems. As computers grew larger, operating systems grew from nonexistant in the mid 1950s to overwhelmingly complex in the late 1960s. IBM's OS-360 project in the mid 1960s almost collapsed under its own weight, falling behind schedule as the development team grew to the point that communication between team members and training new team members took a greater and greater share of the project's resources. This story is told in great detail in F. P. Brooks' book The Mythical Man Month.

  Again, as operating systems grow, the number of different classes of resources grows. You have disk files, network streams, timers, processes, memory segments, and more. There are multiple classes of disk devices, multiple classes of files, and more. Making sense of these was a problem.

A group of programmers working in Oslo, Norway developed the idea of objects, classes, class hierarchy and almost all of the other key concepts of object-oriented programming in the mid 1960's. They came at this from thinking about discrete event simulations, mostly as applied to logistics. If you are moving materials from here to there, you have trucks to move things, but there are different classes of trucks each with different attributes. Semi trucks and pickup trucks are both types of trucks, but you can detatch the trailer from a semi, while you cannot detatch the cargo area of a pickup (ignoring the possible use of a chainsaw on a modern aluminum truck).

This group, led by O.J. Dahl, developed a simulation language called Simula while they were working this out, and as they finally came to understand the consequences of their ideas, they created a distinctly new language called Simula 67 (the target release date was 1967, but since this is software, they were late).

Simula 67 was not a simulation language, it was a completely general purpose object-oriented programming language, the very first of its kind. We get essentially all of our standard terms for object-oriented programming from Simula 67. Some people have gone so far as to describe Simula 67 as an improvement over most of its successors (that includes C++ and Java).

The other important group in this story was a group led by Christopher Strachey at Cambridge University in England. Strachey was as much a theorist as a practical programmer. His group designed a programming language called CPL (there is disagreement about whether the C stood for Christopher's or Cambridge or Combined, but PL stood for Programming Language). Nobody ever succeeded in implementing CPL, but a student implemented a subset called BCPL (Basic CPL).

One of the things that Strachey's group explored was the use of BCPL as an operating system development language. It is important to know that BCPL was not object oriented in any way. It was very primitive, but unlike other languages of the era (with the exception of assembly language), it allowed people to invent just about any kind of programming model they wanted. As Strachey and his associate Joseph Stoy developed a toy operating system called OS6, they discovered the basic ideas of objects, applying them primarily to I/O streams, where all kinds of I/O were implemented essentially as subclasses of a common stream interface class. They did not have object-oriented terminology, but they had the idea.

A group at Bell Labs in Murray Hill, New Jersey set out to build a new operating system in the late 1960s. They called it Unix, and they were quite interested in BCPL, enough so that they designed a new simplified version of BCPL that they named, simply, B. The B project and the first version of UNIX were married when they extended B to support a limited concept of data types. They called this new language C and used it to rewrite UNIX. The internals of Unix, particularly, those involved with input/output, have a strong object-oriented flavor despite the fact that there is no support for objects in C.

When Bjarne Stroustrup, an experienced Simula 67 programmer, was hired by the Unix group at Bell Labs, he was sufficiently annoyed by the lack of support for objects in C that he wrote a C preprocessor that he called C++ that extended C with the features of Simula 67 that he liked. A preprocessor for a programming language takes input in an extended version of that language and produces output in that language. The original C++ preprocessor translated C++ to C. Only after versions of C++ were written outside of Bell Labs was a true C++ compiler written.

By 1980, C++ began its spread outside of Bell Labs and the Unix world. Two things contributed to this: One was BSD Unix, the first version of Unix supported on the then best-selling 32-bit mainframe of the era, the VAX 11/780 made by Digital Equipment Corporation. We bought one here at the University of Iowa, and we ran Unix on it; the story was very similar in universities around the world. The second thing was the GNU C++ compiler, the most important of the early ventures in open-source software development.

At Sun Microsystems in the early 1990s, James Gosling was not happy with the C foundation of C++ and set out to strip away the mistakes that C++ had inherited from C and produce a lightweight language called Java. This had two main selling points: First, it looked like C++ so programmers who knew that language could move to Java with minimal "culture shock." Second, many of the dangerous features of C were disabled. Some early wags described Java as being C++ with training wheels.

Java

We'll be programming in Java, a language many of you know, at least at a shallow level. Don't worry, we will go beyond the shallow level, but first, I want to make sure that everyone is up to speed, so we'll begin at the beginning. Here is the classic Hello World program in Java:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World");
    }
}

It hardly seems worth the effort to add comments to such a minimal program, but we will always add a minimum of commentary to all of our programs. The bare minimum is something like the following:

// HelloWorld.java
/**
 * Program to output the text Hello World to standard output
 * @author Douglas W. Jones
 * @version 8/27/2020
 */
public class HelloWorld {
        public static void main(String[] args) {
                System.out.println("Hello, World.");
        }
}

Here, the first comment in the file is // HelloWorld.java This simply states the file name that this program is expected to occupy. Java (unlike many other programming languages) reqsuires that the file name for a source file match one of the classes defined in that source file, but that class definition may come much later in the file, after many comments, import directives, and even other class definitions. Therefore, in this class, we adopt the requirement that every source file begin with a comment giving the expected name of that source file.

The second comment is written in a special comment language called Javadoc. This is input to a program, also called Javadoc, that builds a web-site that documents Java programs. We will always write at least minimal Javadoc comments for every program we write, and as our programs grow, we will start exploring how Javadoc can help build useful roadmaps to the code we write.

Use a text editor to create this program and then run it!

Hello world is not a very interesting program. Here is a more interesting one. it prints successive members of the Fibonacci series to standard output:

// Fibonacci.java
/**
 * Program to print successive Fibonacci numbers to standard output
 * @author Douglas W. Jones
 * @version 8/27/2020
 */
public class Fibonacci {

        /**
         * Recursive function to compute a Fibonacci number
         * @param i the index of the desired Fibonacci number
         * @return the i'th Fibonacci number
         */
        private static int fib( int i ) {
                if (i < 2) return i;
                return f(i - 1) + f(i - 2);
        }

        /**
         * Main program
         * Calls fib(i) for successive values of i
         */
        public static void main(String[] args) {
                int i = 0;
                while (true) { // compute successive Fibonacci numbers
                        System.out.println( "f(" + i + ")=" + f(i) );
                        i = i + 1;
                }
        }
}

The above program is somewhat overcommented. At this point, these comments do not contribute much to understanding this code, but as the program grows, commentary at about this level of complexity will become essential.