1. Introduction to Programming in Java
AP Computer Science A
Dr. Persin

2. Contents History First Java Application Data types Variables Strings
Assignments
Math, Boolean expressions
Relational operations
If statements
System.exit

3. Very Brief History Started in 1991 by SUN Microsystems
Targeted at consumer electronics. Wanted reliable programming language.
Integrated into browsers
Evolved into write once run anywhere, integrates into Netscape
General purpose libraries released

4. Basic Definitions Java is an object oriented language. Object Method
Class
Applications
Applets
Native classes
Threads
Exceptions

5. First Application /** *Hello World, first application, only output. */
public class hello{
public static void main (String [] args) {
System.out.println(“Hello World”);
} //end main
}//end class

6. Notice: Java is CASE SENSITIVE!! Whitespace is ignored by compiler
Whitespace makes things easier to read…hence it affects your grade 
File name has to be the same as class name in file.
Need to import necessary class definitions

7. Variables Variables: Naming: Name Type Value
May contain numbers,underscore,dollar sign, or letters
Can not start with number
Can be any length
Reserved keywords
Case sensitive

8. Primitive data types Byte 8 -27 27-1 Short 16 -215 215-1 Int 32 -231
231-1
Long 64
Float
Double
Boolean 1
Char

9. Assignment = Example: int n; n = 10; or int n = 10; //same

10. Strings
Not a primitive class, its actually something called a wrapper class
To find a built in class’s method use API documentation.
String is a group of char’s
A character has single quotes
char c = ‘h’;
A String has double quotes
String s = “Hello World”;
Method length
int n = s.length;

11. Using Strings public class hello{
public static void main (String [] args) {
String s = “Hello World”;
System.out.println(s); //output simple string
} //end main
}//end class hello

12. Math Unary Regular math (+,-,*,/) % modulo operator int x = -9;
int y = 3+x;
% modulo operator

13. Incrementing Increment and Decrement i++ equivalent to i = i + 1;
Can also do ++i, which uses i before incrementing it.
Decrementing: i--;

14. Casting int n = 40; Wrong : byte b = n; why??
Right: byte b = (byte) n;
Type casting converts to target type

15. Casting II
Type char is stored as a number. The ASCII value of the character.
A declaration of :
char c = ‘B’; stores the value 66 in location c can use its value by casting to int how??

16. Assignment += -= *= /= %=

17. Boolean Expressions boolean b b will be either true (1) or false (0)
Logical operations: !(not), && (and) || (or)
boolean a,b; a = true; b = false; System.out.println (“a && b is “ + (a && b));

18. Relational Operators == equality != inequality > greater than
< less than
>= greater than or equal to
<= less than or equal to

19. The if - branching statement
if ( x < y) {
x = y; }
if ( x < y ) { x = y; } else { x = 88; }

20. If/Else
if (logic condition) { something } else if (logic condition) { something } else { something else }

21. Nested IF if ( x < 0 ) { System.out.println( “ x is negative “ ); }
else { if ( x > 0 ) { System.out.println ( “x is positive” ); } //end if x > 0 else { System.out.println ( “x is zero “ ); }
} //end else x >=0

22. Switch/Case Switch(variable){ case(1): something; break;
default: something; }

23. Exceptions Java exception object.
java.io.Exception most general one. Some exception like in Throwable class define methods to get the message.

24. try….catch blocks. Try { ……. } catch ( IOException v) { ………. }

25. System.out.println println is a method in the Printstream class.
Defined:
public void println(String x) can be any type of string or combination string using addition to join parts. Example: println(“hello “ + “world “ + x);

26. System.exit() One method in java.lang.System
Defined: public static void exit ( int status)
Terminates currently running Java VM
Status is status code, non zero will usually mean something abnormal.
Used at end to indicate success, or in middle to signal problems.
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