1. Your First Java Application Chapter 2

2. 2 Program Concepts Modern object-oriented programs help us build models to manage the complexity found in a problem domain. The problem domain describes real-world objects and concepts that a computer program is trying to solve.

3. 2 Models A model is a simplification of a complex system. A good model: Helps to identify the most important aspects of a problem. Helps a programmer to focus on the problem he or she is trying to solve instead of on the complexity of the problem’s data.

4. 2 What is a metaphor? A metaphor is a word or phrase used in place of another word or phrase to denote a likeness. Computer programs use “metaphors” to represent real objects.

5. 2 Objects Objects represent real-world things: Ship Rudder Wheel Instruments Objects have: properties (characteristics) methods (behaviors)

6. 2 Classes and Objects A class is a definition of a type: Like a template, a class defines the characteristics and behaviors of the type. An object is an instance of a class: Can be instantiated and manipulated An object’s characteristics are defined by the class that was used to create the object.

7. 2 Fields Fields define the properties of a class. Can be intrinsic types ( int, boolean …) Can be user-defined objects State is the current value of a field in an object.

8. 2 Methods Methods describe the capabilities of the class. Every method must be called from another method. The only exception is main(), which is called by the OS. Methods can accept parameters.

9. 2 Object Relationships Association A method of one object calls the method of another object. Composition Some objects are composed of other objects.

10. 2 Specialization Hierarchies of classes move from a generalized class to a more specific class.

11. 2 Creating Programs Syntax and Semantics A language’s exact keywords, punctuation, and order of terms are called its syntax. Semantics refers to the meaning of one’s instructions; what the program is trying to accomplish.

12. 2 Writing a Java Program Writing a Java program requires five steps: Analyze Design Write Compile Test

13. 2 Compiling the Code Programs must be compiled in order for the CPU to understand and execute the instructions. Java byte code is run through the Java Virtual Machine (JVM), which translates the code for the CPU..java files are compiled by the javac (java compiler) program into.class files.

14. 2 Types of Java Programs Applet Requires an.HTML file with the tag to reference the.class file Can also be run using the appletviewer.exe program file Application Run by the java.exe program file Run without a browser interface, often using the console window

15. 2 HelloWorld.java Analysis The keyword import allows existing class libraries to be reused. The keyword public signifies that a class is visible to other classes. Braces {} indicate the beginning and end of a block of code. Braces must always be “balanced” Align opening and closing braces

16. 2 More HelloWorld.java Analysis The keyword void signifies that a method does not return a value. Identifiers are the names given to classes, fields, and methods. Identifiers are case sensitive. Identifiers often use camel case notation.