Java Review Outline • Java Primitives, Program Structure • Operators, Control Flow, Loops • Classes and Objects Most of these slides are based on “Intro to OOP with Java” text book by C. Thomas Wu
Java Translation • The Java compiler translates Java source code into a special representation called bytecode in the .class file • Java bytecode is not the machine language for any specific CPU • Another software tool, called an interpreter (in our case the Java Virtual Machine), executes the bytecode • Java is considered to be architecture-neutral • The Java compiler is not tied to any particular machine
Program Structure // comments about the class public class MyProgram { } // comments about the method public static void main (String[] args) { } method header method body
Arithmetic Operators Intro to OOP with Java, C. Thomas Wu
Operator Precedence Rules
if( testScore < 70 ) JOptionPane.showMessageDialog(null,"You did not pass"); else JOptionPane.showMessageDialog(null,"You did pass "); Boolean Expression Then Block Else Block Syntax for the if Statement if( <boolean expression> ) <then block> else <else block> Can be visualized as a flowchart Indentation is important!
String str1 = new String("Java"); String str2 = new String("Java"); if(str1 == str2){ System.out.println("They are equal"); }else{ System.out.println("They are not equal"); } Comparing Objects • With primitive data types, we have only one way to compare them, but with objects (reference data type), we have two ways to compare them. • We can test whether two variables point to the same object (use ==), or • We can test whether two distinct objects have the same contents. Sol : They are not equal Discussion of some string methods
Arithmetic Expression switch ( gradeLevel ) { case 1: System.out.print("Go to the Gymnasium"); break; case 2: System.out.print("Go to the Science Auditorium"); break; case 3: System.out.print("Go to Harris Hall Rm A3"); break; case 4: System.out.print("Go to Bolt Hall Rm 101"); break; } Case Label Case Body Syntax for the switch Statement switch( <arithmetic expression> ) { <case label 1> : <case body 1> … <case label n> : <case body n> }
while( number <= 100 ) { sum = sum + number; number = number + 1; } Boolean Expression Statement(loop body) Syntax for the while Statement while( <boolean expression> ) <statement>
Priming Read Example: Testing Input Data String inputStr; int age; inputStr = JOptionPane.showInputDialog(null, "Your Age (between 0 and 130):"); age = Integer.parseInt(inputStr); while(age < 0 || age > 130) { JOptionPane.showMessageDialog(null, "An invalid age was entered. Please try again."); inputStr = JOptionPane.showInputDialog(null, "Your Age (between 0 and 130):"); age = Integer.parseInt(inputStr); }
do{ sum += number; number++; }while( sum <= 1000000 ); Statement(loop body) Boolean Expression Syntax for the do-while Statement do <statement> while( <boolean expression> ) ;
for ( i = 0 ; i < 20 ; i++ ) { number = scanner.nextInt(); sum += number; } 2) Boolean Expression 1) Initialization 4) Increment and back to 2) 3) (loop body) Syntax for the for Statement for( <initialization>; <boolean expression>; <increment> ) <statement>
Import Statements Class Comment Class Name class { Data Members Methods (incl. Constructor) } Defining a Class Let us take a look at Bicycle.java, and BicycleRegistration.java
Creating a Package • The following steps illustrate the process of creating a package name company that includes the Employee class. 1. Include the statement package company; as the first statement of the source file for the Employee class. 2. The class declaration must include the visibility modifier public as publicclassEmployee { ... } 3. Create a folder named company, the same name as the package name. In Java, the package must have a one-to-one correspondence with the folder. 4. Place the modified Employee class into the company folder and compile it. 5. Modify the CLASSPATH environment variable to include the folder that contains the company folder. 6. Include the statement import company.* in the driver class : EmployeePayRaise
double[ ] rainfall; rainfall = new double[12]; double rainfall []; rainfall = new double[12]; Variation 1 Variation 2 An array is like an object! Arrays of Primitive Data Types • What is an Array? Why do we need them? • Array Declaration <data type> [ ] <variable>//variation 1 <data type> <variable>[ ]//variation 2 • Array Creation <variable> = new <data type> [ <size> ] • Example
double[] rainfall = new double[12]; String[] monthName = new String[12]; monthName[0] = "January"; monthName[1] = "February"; … double annualAverage, sum = 0.0; for(int i = 0; i < rainfall.length; i++) { rainfall[i] = Double.parseDouble( JOptionPane.showinputDialog(null, "Rainfall for " + monthName[i])); sum += rainfall[i]; } annualAverage = sum / rainfall.length; The same pattern for the remaining ten months. The actual month name instead of a number. Array Processing
Javadoc and Java Style • General information on javadoc is located at • http://java.sun.com/j2se/javadoc • Detailed reference on how to use javadoc on Windows is located at • http://java.sun.com/j2se/1.5/docs/tooldocs/windows/javadoc.html • Java Style Specifics • http://geosoft.no/development/javastyle.html
Javadoc (cont’d)
