AP CSA Unit 2 - Using Objects

Object

Entity with data and operations that can manipulate the data

Class

Entity that is either:

1.) Program with only static methods

2.) Custom data type for building objects

Method

A sequence of instructions the object follows to perform a task

Parameter

Information needed by the method to complete the task

Argument

Actual data passed to method

Return Value

The information a method provides

Void

Means NO information is returned

Variable

A storage location in computer’s memory

What are the 3 properties for a Variable?

1.) Type of data being stored

2.) Name (identifier)

3.) Contents (Actual data)

int

For storing integer data

int age = 17;

double

For storing precise number data

double gpa = 3.95;

String

A sequence of characters (text)

System.out.println("Plano West")

Simple Numeric Variables

Assignment Operator (=)

Assigns value (contents) to a variable

variable = value;

Variable Syntax

Declaration

Type name;

Initialization

name = value;

Combined (Declaration & Initialization)

Type name = value;

Identifier

Name of variable, class, or method

Rules for Identifiers

1.) May contain letters, digits (0-9), underscore ( _ ) and dollar sign ($) characters

2.) Cannot start with digit

3.) No spaces are permitted

4.) Cannot be a reserved word

5.) Letters are case-sensitive: west, West, and WEST are different!

Reserved Word

Words defined to have special meaning in Java (Ex: int, public, void)

Java Naming Conventions: Variables and Methods

Starts with first word in all lowercase, subsequent words capitalized: myDogSpot

Java Naming Conventions: Classes

Starts with uppercase letter, each word capitalized: PlanoWestWolf

Java Naming Conventions: Constants

All uppercase letters, separate words with : NUMBER_ONE

Comment

Information for humans (programmers) that the compiler ignores

Single-Line Comment

All information to the right of “//” is ignored

//Single-Line Comment

Multi-Line Comment

All information between “/*” and “*/” is ignored

/*	This is
      a multi-line comment
      and is all ignored!
 */

Javadoc

Information can be extracted using tool to create documentation

• Starts with “/**” and ends with “*/”

• Uses special tags like @author, @param and @return

File Heading

A 6-item comment at the top of each source file

Method Comment Heading

Describes the parts of each method

Object Variables

Variable that contains the memory address, or reference, of the object

Its type is the name of a class

Declaring the Object

Designate a name for referring to the object

ClassType name;

Instantiation

Building (constructing) an object by calling on a class’ constructor

name = new ClassType();

Some constructors accept parameters – allowing us to specify initial values

Rock mossy = new Rock(Color.GREEN);

Some constructors accept multiple parameters

Location loc;
loc = new Location(5, 7);

Calling Methods

After instantiating your object, you can call, or invoke, its methods

Public Interface

The methods defined by a class for public use

API (Application Programming Interface)

Defines the public interface for classes and methods in the Java library

Return Method

A method that returns a value when called

Void Method

A method that does not return information

Accessor Method

Does not change the object’s data

Mutator Method

Changes the object’s data

Calling Methods With Objects

Calling Return Methods With Objects

Package

A grouping of logically-related classes

Import Statement

Identifies a class defined in a different package

Overload

Method is defined multiple ways

Concatenation

Joining two strings together to form a new string

int length()

Returns the number of characters (visible + white space) in the string

String school;
school = new String("Plano West");
int count = school.length();
// Returns as 10