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Objects Adapted from: "Introduction to Programming" Dr. Donald Bell, Cal Poly, 1999 (updated April, 2010) Classes & Objects Person Car String a person class (an object from class might be called aJolie) a car class (object will have characteristics and behaviors of a specific car) "hello" "Wendy Le" (objects) Using Objects and Classes Objects receive messages (which cause methods to run) Most statements using objects have the following structure The above statement means object dot method for example: thisPerson.setAge(24); the object whose name is thisPerson is sent the message setAge() along with the "value" 24 This sets the person's age at 24 years old Working with Objects/Classes Most of Java involves working with objects or classes In a Java statement involving objects or classes you must be able to identify the object or class name the message (method) the argument (if any) Sending Messages myCar.setWeight(3500); carWeight = myCar.getWeight(); System.out.println(carWeight); System.out.println("Van Long"); System.out.println(custName); System.out.println("Customer Name: " + custName); Sending Messages to Objects - 2 System.out.println(custName.toUpperCase()); System.out.println("Sam Smith".toLowerCase()); System.out.println("Customer Name: " + custName.toLowerCase()); custResponse = custAnswer.charAt(0); custResponse = custAnswer.toUpperCase().charAt(0); // note method working on results of another method Review the Previous Examples For each of the examples of Java statements on the previous slides make sure you can identify the object and/or class name (or literal object e.g., text) the message(s) sent to the object or class the argument (if any) Naming Exercise view Mouth.java class code problem: mouths speak audibly, not write text e-mail from Mark Lutton replace "Mouth" with some other class name that could output text replace say with some other class method that is appropriate for the new object Exercise: Java Object, Method Documentation Look at Sun's documentation for the Java NumberFormat class Click on the METHOD link near upper left Identify the messages that can be sent to NumberFormat objects Identify arguments that these messages can send to NumberFormat objects Click the All Classes link near the upper right to see a list of all classes in Java