1. Basic Java structural components
Chapter 3
Basic Java structural components

2. This chapter discusses
Some Java fundamentals.
The high-level structure of a system written in Java.
packages
compilation units
Some fundamental elements that make up a Java program.
identifiers
literals

3. Creating a Software System
Define the classes that will provide the objects.
A class definition determines the features and behavior of the objects that are instances of the class.
A program source is a collection of class definitions.

4. Packages
A system definition is composed of a number of modules called packages.
A package is a collection of one or more closely related classes.
public class: a class that is accessible throughout the entire system.

5. Compilation unit
A source file containing the definition of one or more classes of a package.
It can contain the definition of at most one public class.

6. Identifiers
Sequences of characters that can be used to name things in a Java program.
packages
classes
objects
properties
features

7. Identifiers (cont.) A sequence of letters, digits, ‘$’s, and/or ‘_’s.
Cannot begin with a digit.
Case sensitive: ‘A’ and ‘a’ are considered different!!!

8. Identifiers (cont.) Legal: Illegal:X
Abc
A_a_x
b$2
aVeryLongIdentifier
b29
a2b $_
$$$
IXLR8
Illegal:
2BRnot2B
a.b
Hello!
A-a
A+a
All different identifiers: total Total TOTAL tOtAl

9. Identifiers already in “use”
Called reserved or key words
For example:
package if
class else
public for
int float
interface abstract
private boolean
char import
implements extends

10. Choosing identifiers Choose descriptive names. Student or Textbook
not S or Thing
Avoid overly long identifiers.
HoldsTheNumberOfIterationsOfLoop
Avoid abbreviations; if you abbreviate, be consistent.
Wrong: clientRec and studentRecord

11. Choosing identifiers (cont.)
Be as specific as possible.
Take particular care to distinguish closely related entities.
Effective Less-Effective
newMasterRecord masterRecord1
oldMasterRecord masterRecord2
Don’t incorporate the name of its syntactic category in its name.
Not Recommended: StudentClass

12. Literals Sequences of characters that denote particular values.
We include literals in our programs to denote specific values.
They represent values in a “literal” sense

13. Type int Literals Whole numbers -- both positive and negative.
Commas, periods, and leading zeros are not allowed in ‘int’s.
Legal:
Illegal:
123,

14. Type double Literals Numbers that involve decimal points. 0.5 -2.67 2. .6
Digits before and after the decimal point are preferred.

15. Exponential Notation Used to represent double values.
The “e” can be upper or lower case
The mantissa need not contain a decimal point

16. Type char literals
Single characters between apostrophes (single quotes).
‘A’ ‘a’ ‘2’ ‘;’ ‘ ’
3 characters cannot be represented as themselves:
‘  ‘\’’ (apostrophe)
“  ‘\”’ (quotation mark)
\  ‘\\’ (backslash)

17. Type boolean literals Only 2 possible literals true (Not TRUE or True)
false

18. General lexical rules
A source file is made up of tokens: identifiers, keywords, literals, and punctuation marks.
Spaces and line ends are somewhat arbitrary.
“White” spaces (tabs, carriage returns, spaces) are required between words:
Wrong: publicclass Student

19. General lexical rules (cont.)
Spaces are not required, but are permitted, around punctuation.
All correct examples:
public class Student{
public class Student {
a+b
a + b
Extra spaces and line endings are allowed:
public class Student {

20. General lexical practices
Be consistent in spacing and line endings to make your programs as readable as possible.
Use uniform indentation levels to indicate logical levels in code.
Adhere to accepted industry style conventions for added readability.

21. Comments
Explanatory remarks are included in a program for the benefit of human readers, but are ignored by the compiler.
Use // to treat the remainder of the line as a comment.
Use /* and */ to begin and end a section or multi-line comment.
/* This is a multi-line or
section comment */

22. To recap Fundamental structure of a Java program. Packages
Class definitions and compilation units
Instances of classes
Lexical structure
Identifiers
Literals
Comments