Introduction to Programming in Java AP Computer Science A Dr. Persin www.Lnk2Lrn.com

Contents History First Java Application Data types Variables Strings Assignments Math, Boolean expressions Relational operations If statements System.exit www.Lnk2Lrn.com

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 www.Lnk2Lrn.com

Basic Definitions Java is an object oriented language. Object Method Class Applications Applets Native classes Threads Exceptions www.Lnk2Lrn.com

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 www.Lnk2Lrn.com

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 www.Lnk2Lrn.com

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 www.Lnk2Lrn.com

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 www.Lnk2Lrn.com

Assignment = Example: int n; n = 10; or int n = 10; //same www.Lnk2Lrn.com

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; www.Lnk2Lrn.com

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 www.Lnk2Lrn.com

Math Unary Regular math (+,-,*,/) % modulo operator int x = -9; int y = 3+x; % modulo operator www.Lnk2Lrn.com

Incrementing Increment and Decrement i++ equivalent to i = i + 1; Can also do ++i, which uses i before incrementing it. Decrementing: i--; www.Lnk2Lrn.com

Casting int n = 40; Wrong : byte b = n; why?? Right: byte b = (byte) n; Type casting converts to target type www.Lnk2Lrn.com

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?? www.Lnk2Lrn.com

Assignment += -= *= /= %= www.Lnk2Lrn.com

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)); www.Lnk2Lrn.com

Relational Operators == equality != inequality > greater than < less than >= greater than or equal to <= less than or equal to www.Lnk2Lrn.com

The if - branching statement if ( x < y) { x = y; } if ( x < y ) { x = y; } else { x = 88; } www.Lnk2Lrn.com

If/Else if (logic condition) { something } else if (logic condition) { something } else { something else } www.Lnk2Lrn.com

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 www.Lnk2Lrn.com

Switch/Case Switch(variable){ case(1): something; break; default: something; } www.Lnk2Lrn.com

Exceptions Java exception object. java.io.Exception most general one. Some exception like in Throwable class define methods to get the message. www.Lnk2Lrn.com

try….catch blocks. Try { ……. } catch ( IOException v) { ………. } www.Lnk2Lrn.com

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); www.Lnk2Lrn.com

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. For more practice go to http://www.javabat.com www.Lnk2Lrn.com