OOP: Java Overview java-2

1. OOP: Java Overview ( java-2.ppt) Operators Applications : I/O � Streams, Console, Swing Dialogues Introduction to arrays Arrays of String objects Javadoc GUI applications

2. ?: operator ex 1: max = (i > j) ? i : j; same as if-else above expression returns one of 2 values i or j based on boolean condition (i > j). If condition is true, returns i else returns j ex2: ovHours = (hours > 40) ? (hours - 40 ) : 0;

3. Java I/O � Streams Consistent usage Input: keyboard, file, network connection Output: monitor, file, network connection Standard predefined streams System.In - keyboard System.Out � monitor Note: Gittleman text uses different technique to handle Java I/O javax.swing package for input dialogue Ex1: CalculatePay.java p.71 EX2: Temperature.java p. 84 (shows formatting)

4. I/O Through Objects  online Java tutorial uses generic I/Othrough streams In program must 1st create objects for I/O To create I/O objects, Java uses predefined class library components For efficiency, convert byte streams to buffered String objects We�ll use: stdIn (for keyboard) .. Like cin in C++ stdOut (for monitor) .. Like cout in C++ stdErr (for prompts & error msg) .. Like cerr in C++ Usage: stdOut.println(�Hello World!�); name = stdIn.readLine(); System.Err -used for prompts & error messages System is a predefined class

5. Redefine standard I/O streams Use BufferedReader & PrintWriter classes since they process a string of characters. (Defined in java.io package) Redefine the standard input stream (System.in) as object stdIn We can now use the predefined readline() method to store a string. String name = stdIn.readline(); Redefine the standard output stream(System.out) as object stdOut Use this code in your Java applications: private static BufferedReader stdIn = new BufferedReader (new InputStreamReader(System.in)); private static PrintWriter stdOut = new PrintWriter(System.out, true);

6. Demo: First I/O Program // FirstIO.java - uses standard I/O streams import java.io.*; public class FirstIO { private static BufferedReader stdIn = new BufferedReader (new InputStreamReader(System.in)); private static PrintWriter stdOut = new PrintWriter(System.out, true); public static void main (String[] args) throws IOException { stdOut.println ("Enter your name: "); String name = stdIn.readLine(); stdOut.println ("Your name is: " + name); } }

7. Wrappers & Numeric Input // Age.java Numeric input through I/O streams import java.io.*; public class Age { private static BufferedReader stdIn = new BufferedReader (new InputStreamReader(System.in)); private static PrintWriter stdOut = new PrintWriter(System.out, true); public static void main (String[] args) throws IOException { int age; // local variable stdOut.println ("Enter your age: "); age = Integer.parseInt (stdIn.readLine()); ++age; stdOut.println ("Next year, you will be " + age); } }

8. I/O Buffers For efficiency, input and output data is buffered and processed when the buffer fills up You explicitly flush the output buffer with a method called flush. println() automatically flushes the output buffer print() does not

9. Swing Dialogues for I/O Console application can use Swing package for Recent Java addition Uses a JOptionPane predefined class Use import javax.swing.JOptionPane to import JOptionOption class Use import javax.swing.* to import all swing classes Uses showInputDialog & ShowMessageDialogue methods Technique used in Gittleman Text

10. Swing Dialogues for I/O // Use Swing package for I/Oimport javax.swing.JOptionPane;public class Add { public static void main(String[] args) { int n1, n2; String input;  input = JOptionPane.showInputDialog("Enter the first number"); n1 = Integer.parseInt(input); input = JOptionPane.showInputDialog("Enter the second number"); n2 = Integer.parseInt(input);  JOptionPane.showMessageDialog(null,"The result is " + (n1 + n2));  }}

11. Arrays An array is an indexed collection of data of the same type Each �cell� has a value and an index (index always start at zero!) For n elements, index runs from 0 to (n-1) Array declaration requires array type and use of bracket operator [] type varName[]; Need to allocate memory for the cells int[] scores = new int[10]; char[] vowels = new char[5];

12. Storing Values in the Array We can assign values when we declare the array using an initializer list int [] scores = {100, 99, 95, 100, 80}; (this declares an array of size 5) or by assigning the values directly to the cells final int SIZE = 100; int[] scores = new int[SIZE]; for(int k = 0; k != SIZE; k++) scores[k] = 10 * k;

13. Arrays of Primitives or Objects Array types can be primitives or objects (Strings for example) float [] scores; // reference, not scalars !! char[] vowels; String[] names; // object types Integer[] arr; // object type

14. Arrays in Java An array in Java is an object It is always passed as reference, not value it has a field named �length�: int size = arr.length;

15. Static & Dynamic Arrays In general, arrays are static (size is fixed and predetermine) It�s possible to have a �variable� to control the size of the array int size; size = Integer.parseInt(stdIn.readLine()); int[] numbers = new int [size];

16. Arrays Array reference vs creating array itself Create a ref to array, then create array object with new operator 2 step declaration int[] a; // declares a ref to an int type object a = new int[5]; // declares the actual array object and its size 1 step declaration: ==> int[] a = new int[5];

17. Array Code Examples Primitives � data input, search, passing arrays ArraySlots MaxScore ArrayInputAvg PassArray TryArray String Objects SearchTester PhoneBookTester RollCall @ BYU JavaHelp site

18. Javadoc Automatic documentation generator creates an HTML document format /** * @version * @author * @see * @param * @return * */ See Circle javadoc example in my Code Examples Web Page

19. GUI applications Eliminate HTML page that invokes applet Derive the new class from Frame, implement WindowListener Constructor in new class instead of init() Add main method to invoke the application Set the window�s width and height See 1.1.5 AwtApplication, CustomFrame