Exam Review 10/01/2014 Happy October

The Exam  Will be in Canvas  Two parts  Part A is recall – closed book, closed notes ◦Quizzes, in class activity ◦Know the terminology ◦Be able to evaluate expressions  Part B is coding – open book, closed notes, closed “examples” ◦You will have a shell program that you will need to fill in ◦Prompts are given in the program itself ◦You may use whatever editor you prefer ◦You may NOT use code from labs since they were done with a partner.

Lab EnergyDriver Energy public kineticEnergy(double mass, double velocity) public static…main() { Energy ed; ed = new Energy() energy = ed.kineticEnergy(100, 30); }

What is tester? Energy tester; tester tester = new Energy() kineticEnergy tester contains a reference to an Energy object. The object has [data] and methods.

Primitive vs Reference types PRIMITIVE  The space at declaration time holds the value.  There are only 8. ◦byte ◦short ◦int ◦long ◦float ◦double ◦char ◦boolean REFERENCE  The space at declaration time holds the reference to the value (object).  There are as many as you want to make.  Examples include: ◦DecimalFormat ◦Scanner ◦String ◦NumberFormat

Primitives, cont  We think of primitive containers as holding values.  Java can widen primitives to match the larger types but can only narrow by using the cast operation.  int count;  double sum;  count = sum is illegal, but  count = (int) sum is legal since we are saying take the integer part only.

1-7 Object-Oriented Programming Object Attributes (data) typically private to this object Methods (behaviors / procedures) Other objects Programming Interface

Calling methods “static”  Examples: Math class  No need for a specific version of Math. You are just using its functions.  total = Math.pow(25.0, 3);  value = Math.abs(-250 * 4);  value = Math.abs(Math.pow( * 4); not static  Examples: String class  Which String do we mean? object or specific set of data.  String message;  message = “CS 139 Exam”;  size = message.length();  part = message.substring(5);

5-9 void Methods and Value-Returning Methods  A void method is one that simply performs a task and then terminates. System.out.println("Hi!");  A value-returning method not only performs a task, but also sends a value back to the code that called it. int number = Integer.parseInt( " 700 " );  It is possible to have a value returning method not save the result. keyboard.nextLine(); // consume the new line static method, class name non static method, must have an object. This was created by declaring keyboard to be a Scanner then instantiating the Scanner.

5-10 Parts of a Method Header public static void displayMessage () { System.out.println("Hello"); } Method Modifiers Return Type Method Name Parameter List

5-11 Calling a Method  A method executes when it is called.  The main method is automatically called when a program starts, but other methods are executed by method call statements. displayMessage();  Notice that the method modifiers and the void return type are not written in the method call statement. Those are only written in the method header.  Examples: SimpleMethod.java, LoopCall.java, CreditCard.java, DeepAndDeeper.javaSimpleMethod.javaLoopCall.javaCreditCard.java DeepAndDeeper.java

5-12 Passing a Reference as an Argument showLength(name); public static void showLength(String str) { System.out.println(str + " is " + str.length() + " characters long."); str = "Joe" // see next slide } address “Warren” Both variables reference the same object The address of the object is copied into the str parameter.

5-13 String s are Immutable Objects  String s are immutable objects, which means that they cannot be changed. When the line str = "Joe"; is executed, it cannot change an immutable object, so creates a new object.  See example: PassString.javaPassString.java address “Warren” “Joe” The name variable holds the address of a String object The str variable holds the address of a different String object

5-14 Defining a Value-Returning Method public static int sum(int num1, int num2) { int result; result = num1 + num2; return result; } Return type This expression must be of the same data type as the return type The return statement causes the method to end execution and it returns a value back to the statement that called the method.

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