Introduction to Java Applications

1
Introduction to Java Applications

• Chapter 2

2

• // Fig. 2.1 Welcome1.java
• // Text-printing program.
• public class Welcome1
• // main method begins execution of Java
  application
• public static void main( String args )
• System.out.println( "Welcome to Java
  Programming!" )
• // end method main
• // end class Welcome1
• Welcome to Java Programming!

3
Comments

• // single-line comment
• / / multi-line comment
• / / Javadoc comment
• Javadoc comments can be read by the javadoc
  utility to produce HTML documentation.

4
Case-sensitive

• Java is case sensitive.
• Using system.out.println instead of
  System.out.println is an error.
• By convention, class names should begin with an
  uppercase letter.

5
Filenames

• The filename must match the name of the public
  class defined inside the file.
• Error if not.

public class Car
Filename Car.java
6
Filenames

• Java source files must have the .java extension.
  Wont compile if not.

public class Car
Filename Car.java
7
Filenames
public class Car
Filename Car.java
javac Car.java // compile
bytecode
Filename Car.class
java Car // execute
8
Main

• The main method is the starting point of a Java
  application
• public static void main(String args )

9
Printing

• System.out is the standard output object.
• System.out.println(..) // prints a line
• System.out.print(.) // prints on same line

10

• // Fig. 2.3 Welcome2.java
• // Printing one line of text with multiple
  statements.
• public class Welcome2
• // main method begins execution of Java
  application
• public static void main( String args )
• System.out.print( "Welcome to " )
• System.out.println( "Java Programming!" )
• // end method main
• // end class Welcome2
• Welcome to Java Programming!

11

• // Fig. 2.4 Welcome3.java
• // Printing multiple lines with a single
  statement.
• public class Welcome3
• // main method begins execution of Java
  application
• public static void main( String args )
• System.out.println( "Welcome\nto\nJava\nProg
  ramming!" )
• // end method main
• // end class Welcome3
• Welcome
• to
• Java
• Programming!

12
Escape Characters

• \n newline
• \t tab
• \r carriage return
• \\ backslash
• \ quote

13
Printf

• The C language used the printf function to print
  text.
• printf made use of a string containing
  placeholders.
• Examples are s for strings, d for numbers.
• A new feature in J2SE 5.0 is the printf method of
  the standard output stream.

14

• // Fig. 2.6 Welcome4.java
• // Printing multiple lines in a dialog box.
• public class Welcome4
• // main method begins execution of Java
  application
• public static void main( String args )
• System.out.printf( "s\ns\n",
• "Welcome to", "Java Programming!" )
• // end method main
• // end class Welcome4
• Welcome to
• Java Programming!

15
Inputting

• System.in is the standard input stream.
• The Scanner class is used to read from the
  standard input stream.
• To use the Scanner class, we must import its
  package at the top of our program.
• Once a Scanner object is created, its nextInt()
  method can be called to find the next integer of
  input.

16
import java.util.Scanner // program uses class
Scanner public class Addition // Fig. 2.7
Addition.java, displays the sum of two
numbers. // main method begins execution of
Java application public static void main(
String args ) // create Scanner to
obtain input from command window Scanner
input new Scanner( System.in ) int
number1 // first number to add int
number2 // second number to add int sum
// sum of number1 and number2
System.out.print( "Enter first integer " ) //
prompt number1 input.nextInt() // read
first number from user System.out.print(
"Enter second integer " ) // prompt
number2 input.nextInt() // read second number
from user sum number1 number2 // add
numbers System.out.printf( "Sum is d\n",
sum ) // display sum // end method main
// end class Addition
17
Arithmetic

• Example
• z p r q w/x y
• 6 1 2 4 3 5 // order of
  evaluation

18
Equality and Relational Operators

• Equality operators , !
• Relational operators gt,lt,gt,lt
• These operators associate left to right.
• Equality operators have lower precedence than the
  relational operators.

19
int number1 777 // first number to
compare int number2 777 // second number
to compare if ( number1 number2 )
System.out.printf( "d d\n", number1,
number2 ) if ( number1 ! number2 )
System.out.printf( "d ! d\n", number1,
number2 ) if ( number1 lt number2 )
System.out.printf( "d lt d\n", number1,
number2 ) if ( number1 gt number2 )
System.out.printf( "d gt d\n", number1,
number2 ) if ( number1 lt number2 )
System.out.printf( "d lt d\n", number1,
number2 ) if ( number1 gt number2 )
System.out.printf( "d gt d\n", number1,
number2 )
777 777 777 lt 777 777 gt 777
20
End of Slides