comments are for people header comments supply basic information about the artifact
TRANSCRIPT
Start of every class Start up DrJava
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Read entire class entry
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Try to figure out why the picture and title for the day are appropriate
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Comments are for people
Header comments supply basic information about the artifact
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Comments also used to describe class elements
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Whitespace is also for people
Blank lines make elements stand out
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Indentation is a form of whitespace
Indentation is used to indicate that what follows is a part of what proceeded
Indentation is a form of whitespace
Indentation is used to indicate that what follows is a part of what proceeded
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Keywords are reserved lowercase words that have special meaning
public – what follows is shareable
class – program or object definition
static – not part of an object definition
void – method does not return a value
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Name of the class
A Java name must be an identifier
Java has syntax rules for stating what is a valid name; e.g., identifiers begin with letter and can be followed letters and numerals
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
To encourage program understanding style rules give name understanding
Convention to capitalize the first letter in a class name
General convention to capitalize successive words in a name
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
PrintQuote, main, String, args, System, out, and println are all names
Convention that identifiers not indicating a class begin with a lower case letter
Braces delimit a class definition
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Braces delimit a block of code
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
A program begins executing the code in method main()
Method main() must be public, static, and void
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Every method has a parameter list following its name.
The list is contained with a pair of parentheses.
For some methods, the list is empty
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Method main() takes a single parameter of type String[]
Everybody who is anybody calls that parameter, args
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Following the parameter list is the body of the method
The method body lists the statements (i.e., actions) it is to perform when invoked (started up)
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
The statements are performed from top to bottom
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
The statements are performed from top to bottom
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Because statements are allowed in general to span multiple lines an indicator is needed for separating statements from one another
Java statements are terminated with a semicolon
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
The dot is the selection operator
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
Sometimes multiple selecting is needed to get a hold of the desired component
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
System is the name of a class library whose elements are automatically available to a program
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
The System library has an element named out
out represents an object configured to be associated with your display
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
out has a println() behavior
println() is a method
println() displays text to its display
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
println() displays the value of its argument
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
This use of println() says to print the literal string ”I’m never going to the Louvre again.” to its display
A literal string is a sequence of characters within a pair of the double-quote characters
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
This use of println() says to print the literal string ”-- Joanne Cohoon” to its display
// author: J. P. Cohoon
// email id: jpc
// purpose: print text
public class PrintQuote {
// method main(): program starting point
public static void main( String[] args ) {
System.out.println( "I’m never going to the Louvre again." );
System.out.println( "-- Joanne Cohoon." );
}
}
A program terminates when all of the statements in method main() are completed