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Introduction to Programming in Java

Introduction to Programming in Java. AP Computer Science A Dr. Persin. Contents. History First Java Application Data types Variables Strings Assignments Math, Boolean expressions Relational operations If statements System.exit. Very Brief History. Started in 1991 by SUN Microsystems

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Introduction to Programming in Java

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

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

  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 www.Lnk2Lrn.com

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

  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 www.Lnk2Lrn.com

  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 www.Lnk2Lrn.com

  7. Variables • Variables: • Name • Type • Value • Naming: • May contain numbers,underscore,dollar sign, or letters • Can not start with number • Can be any length • Reserved keywords • Case sensitive www.Lnk2Lrn.com

  8. Primitive data types www.Lnk2Lrn.com

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

  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; www.Lnk2Lrn.com

  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 www.Lnk2Lrn.com

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

  13. 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

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

  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 ccan use its value by casting to inthow?? www.Lnk2Lrn.com

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

  17. Boolean Expressions • boolean bb 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

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

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

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

  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 > 0else {System.out.println ( “x is zero “ );} } //end else x >=0 www.Lnk2Lrn.com

  22. Switch/Case • Switch(variable){ case(1): something; break; case(23): something; break; default: something; } www.Lnk2Lrn.com

  23. 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

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

  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); www.Lnk2Lrn.com

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

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