02/14/2005

Introduction to Programmingwith Java, for Beginners

Midterm 1 Review

02/14/2005 CSE 110 2

Overview

A Java program is a collection of cooperating objects

An object is an instance of a classAll Java code exists within a classTop Down Design

Analyze the problem/simulation/game Decide what classes to use to model it

Bottom Up Programming Write code for a class/method a little at a time

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Object “state” and “behavior”

An object has “state” Instance variables that hold its data

An object has “behavior” Methods that perform actions like computations,

reporting information about state (“getters”), changing state (“setters”)

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Protecting an Object’s State

A software designer wants his/her objects to behave: Consistently and reliably According to “spec” (specification) True to its documentation (javadocs)

This is accomplished in part by: Making instance variables private Providing public methods that access the state

appropriately

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Object Creation

An object is an instance of a class A class has one or more constructors A constructor:

Is a piece of code with the same name as the class Is executed when an object is created with the “new”

operator When the “new” operator is used, Java finds the right class

and then runs the constructor that has right number, order, and types of parameters

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Variables

Variable Types Primitive Reference

Variable Scope Instance Variable (a.k.a. “dynamic” variable, field) Method/constructor Parameters Local Variables

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ExpressionsAn expression has a value. Some examples: Arithmetic

3 + 5 X * 2

Relational >, >=, <, <=, ==, !=

Boolean true, false, &&, ||, !

Assignment (value is the value assigned) Method call (value is the value returned by method)

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Statements

A statement causes an action. Statements end with a semicolon or a {block} Unlike an expression, a statement does not have a value Some examples:

Variable declaration Assignment Method call if while for

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Arrays

A way to easily declare many variables of the same type An array is an object Whenever you see [ ] in a Java/C/C++/C# program, that

means array Provide random access Legal indices: 0 through (length - 1) If attempt to access via an illegal index:

ArrayOutOfBoundsException