Java How to Program Fourth Edition - DCC

Chapter 4 Control Structures: Part 1 151
During the 1960s, it became clear that the indiscriminate use of transfers of control was
the root of much difficulty experienced by software development groups. The finger of
blame was pointed at the goto statement (used in several programming languages,
including C and Basic), which allows the programmer to specify a transfer of control to one
of a very wide range of possible destinations in a program. The notion of so-called structured
programming became almost synonymous with “goto elimination.” Java does not
have a goto statement; however, goto is a reserved word and should not be used in a Java
program.
The research of Bohm and Jacopini 1 had demonstrated that programs could be written
without any goto statements. The challenge of the era for programmers was to shift their
styles to “goto-less programming.” It was not until the 1970s that programmers started
taking structured programming seriously. The results have been impressive, as software
development groups have reported reduced development times, more frequent on-time
delivery of systems and more frequent within-budget completion of software projects. The
key to these successes is that structured programs are clearer, easier to debug and modify
and more likely to be bug free in the first place.
Bohm and Jacopini’s work demonstrated that all programs could be written in terms of
only three control structures—namely, the sequence structure, the selection structure and
the repetition structure. The sequence structure is built into Java. Unless directed otherwise,
the computer executes Java statements one after the other in the order in which they
are written. The flowchart segment in Fig. 4.1 illustrates a typical sequence structure in
which two calculations are performed in order.
A flowchart is a graphical representation of an algorithm or a portion of an algorithm.
Flowcharts are drawn using certain special-purpose symbols, such as rectangles, diamonds,
ovals and small circles; these symbols are connected by arrows called flowlines, which indicate
the order in which the actions of the algorithm execute.
Like pseudocode, flowcharts are often useful for developing and representing algorithms,
although pseudocode is strongly preferred by many programmers. Flowcharts show
clearly how control structures operate; that is all we use them for in this text. The reader
should carefully compare the pseudocode and flowchart representations of each control
structure.
add grade to total total = total + grade;
add 1 to counter counter = counter + 1;
Fig. Fig. 4.1 4.1 Flowcharting Java’s sequence structure.
1. Bohm, C., and G. Jacopini, “Flow Diagrams, Turing Machines, and Languages with Only Two
Formation Rules,” Communications of the ACM, Vol. 9, No. 5, May 1966, pp. 336–371.
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