Objective C And Java

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About the Speaker

Jonathan Lehr, About Objects

1991–2001: Objective-C developer and trainer

NEXTSTEP (precursor to Mac OS X and Cocoa)

WebObjects (web app framework and ORM)

2001–2008: Java EE developer

Fannie Mae and US Govt web app projects

Framework developer

Co-author of Jakarta Pitfalls and Mastering JavaServer Faces

Now: iPhone developer and trainer

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About Objects

Reston Town Center (Accenture Building)

iPhone OS and MacOS X

Cocoa Programming Workshop

iPhone Programming Workshop

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Overview

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What is Objective-C?

Superset of ANSI C

Adds object-oriented capabilities to C language

Runtime system (C library)

Dynamic typing

Dynamic binding

GNU C compiler compiles C and Objective-C

Apple donated Objective-C to GNU project (open source)

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Who Uses Objective-C?

Primarily Apple

Mac OS X

Cocoa (UI framework)

Several other smaller frameworks (Core Animation, Core Data, etc.)

iPhone OS

Cocoa touch (UI framework)

Several other smaller frameworks (Core Animation, Core Data, etc.)

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Why Should I Care (as a Java Dev)?

Cool approaches to problems can open door to new design ideas

Some enterprise projects may need to integrate with iPhone apps

Doesn't hurt to have more perspective on how client apps work

Enterprises starting to write custom iPhone apps

Managers might ask you for technical info, opinions

Might even draft you for an iPhone development effort

Might want to tinker with iPhone app development for fun or

profit in spare time

Trust me—It is a lot of fun!

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History

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Where Did Objective-C

Come From?

Inspired by SmallTalk

1972 – Alan Kay, Xerox PARC

Alto workstation

First Objective-C compiler

1983 – Brad Cox, StepStone

First major licensee

1985 – Steve Jobs, NeXT Computer

Used to develop UI for NEXTSTEP OS

(and later, OpenStep)

Xerox Alto

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NeXT, Inc.'s NeXTCUBE

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NEXTSTEP Timeline

1989 – NEXTSTEP 1.0

1992 – NEXTSTEP 486 for Intel

1994 – NeXT/Sun OpenStep spec.

1996 – OPENSTEP 4.0 released

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Apple + NeXT

Late 1996

Apple's Copland stalls

Goal had been to develop modern OS

to replace Mac OS 9

Apple decides to acquire third-party

OS instead

Buys NeXT, Inc for $440 million

Steve Jobs comes onboard as unpaid, part-time consultant

Result: NeXT takes over Apple

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What Apple Bought in 1996

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From OpenStep to Mac

+ Mac OS 9 compatibility environment

+ Quartz rendering engine

Replacement for Display Postscript + Objective-C UI layer rebranded 'Cocoa'

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iPhone OS

Port of Mac OS X

Shares same developer toolset

Developer frameworks adapted and scaled down for mobile device

iPhone OS 2.0b2

March, 2008

Initial release of iPhone OS

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Platforms

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Layered Architecture

C libraries and system calls

Core Services (C libraries and Objective-C frameworks)

Media Layer (C libraries and Objective-C frameworks)

Cocoa (Mac OS) and Cocoa touch (iPhone OS)

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Core Services

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Core Foundation C Library Strings, dates, collections, threads, etc

Address Book Framework Managing contact info

CFNetwork C Library Low-level network access

Core Location Framework Accessing geospatial positioning info

Security Framework Manages certificates, public/private keys, etc

SQLite C Library Accessing lightweight SQL database

XML Support ObjC Class NSXMLParser class

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Open GL ES Core Graphics Core Animation

Core Audio

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iPhone SDK

Cocoa Touch Media

Core OS

Core Services

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Cocoa Touch

UIKit Foundation Framework

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Foundation Framework

Wrappers for strings, numbers, dates, binary data

Collection classes (arrays, sets, dictionaries, etc.)

Bundles (dynamically loadable app modules)

User preferences

Threads and run loops

Files, streams and URLs

Bonjour (dynamic discovery)

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UIKit

Application management and integration (via URL schemes)

Graphics and windowing

Handling touch events

User interface views and controls

Text handling

Web content

Device-specific features (accelerometer, camera, photo library)

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Developer Tools

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Automatically maintains build scripts

Displays logical groupings of files

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Interface Builder

Visual GUI design tool

Doesn't generate code

Works with ‘Freeze-dried’ objects

Archived (serialized) in .nib files

Dynamically loaded

Objects deserialized at load time

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Syntactic Differences

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Object Data Types

Objective-C objects are dynamically allocated structs

Variable types are therefore pointers to struct defined by class

Java:

Employee emp = new Employee();

Objective-C

Employee *emp = [[Employee alloc] init];

Obj-C also provides generic object type, id

id emp2 = [[Employee alloc] init];

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Constructors vs Creation Methods

No constructors; creation methods are just methods

Ordinary return statements provide more flexibility

Calls to super can occur anywhere within a method

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Prefix vs Package Path

Obj-C language doesn't provide namespaces

Frameworks and libraries use prefixes by convention to avoid

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Method Prototypes

Methods declared in h, implemented in m

Data types enclosed in parens

Instance methods prefixed with

-Class methods prefixed with +

// Method declarations

- (id)init;

+ (id)alloc;

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No Method Overloading

Runtime system looks up methods by name rather than signature

Makes introspection simpler and more efficient

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Multi-Argument Methods

Method names can be composed of multiple sections

Each section ends with a colon that delimits the next arg

Java:

public void addEmployee(Employee emp, String title)

Objective-C

- (void)addEmployee:(Employee *)emp

withTitle:(NSString *)title

Name of method is addEmployee:withTitle:

Args are emp and title

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Instance variable section inside curly braces

Methods defined outside curly braces

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Anatomy of a Class Declaration

@interface Person : NSObject {

int _age ; NSString * _firstName ; }

@end

compiler directive

class we're declaring class it inherits from

name of instance variable data type

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Class Declaration: Methods

@interface Person : NSObject {

// Instance variables go here

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- ( void )setFirstName:( NSString *)firstName {

// Note: Omits some memory management details

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No visibility modifiers for methods

Methods made 'private' by omitting declarations from h file

To emphasize 'privacy', prefix method name with underscore

Intent:

Obj-C: Makes obvious what you shouldn't do

Java: Makes impossible what you shouldn't do

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@interface Person : NSObject

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Memory Management

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Garbage Collection

Objective-C 2.0 (Nov., 2007) provides GC on Leopard (OS X 10.5)

GC not available on iPhone for performance reasons

iPhone apps use autorelease pools and a built-in reference counting

system to provide partial automation

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Reference Counting

NSObject (root class) includes reference counting API

- (id)retain; // Increments retain count

- (id)release; // Decrements retain count

- (id)autorelease; // Delayed release

- (void)dealloc; // Called by release when retainCount == 0

Creation methods set retain count to 1

Methods whose names begin with alloc or new, or contain the word

copy

Calls to these methods or to retain must be paired with calls to release

or autorelease You never call dealloc directly.

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// Deallocate anything we've retained or copied

[ _firstName release ]; // Release the previous one

_firstName = [firstName copy ]; // Retain or copy the new one

}

Managing Reference Counts

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Declared Properties (Obj-C 2.0)

Shorthand for declaration of getter/setter pair

@property (nonatomic, retain) NSString *firstName;

// The above line is a replacement for these two

- (NSString *)firstName;

- (void)setFirstName:(NSString *)firstName;

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Synthesizing Accessor Methods

Declared properties allow compiler to synthesize getter/setter

methods

Add the following after @implementation in m file:

@synthesize firstName = _firstName;

Equal sign and ivar name can be omitted if ivar name is the same as

getter name

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Foundation Framework

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NSObject

Implements introspection

Implements protocols for important mechanisms

Key-Value Coding (NSKeyValueCoding)

Key-Value Observing (NSKeyValueObserving)

Defines protocols for copying and serialization

NSCopying

NSMutableCopying

NSCoding

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Mutable vs Immutable

NSMutableString is subclass of NSString

To obtain a mutable copy of an NSString:

NSString *s1 = @"Fred";

NSMutableString *s2 = [s1 mutableCopy];

[s2 appendString:@" Smith"];

Same pattern followed for other mutable/immutable class pairs

Example: NSArray and NSMutableArray

NSArray *a1 = [NSArray arrayWithObjects:@"One", @"Two", nil]; NSMutableArray *a2 = [a1 mutableCopy];

[a2 addObject:@"Three"];

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Value Classes

NSValue is wrapper class for primitive values and binary data

Subclasses: NSData, NSNumber, NSDecimalNumber

Simple API

NSNumber *n = [NSNumber numberWithFloat:3.5];

int x = [n intValue];

NSString also has simple API for primitive values

NSString *s = [NSString stringWithFormat:@"%f", 3.5];int x = [s intValue];

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Reading/Writing Files and URLs

Strings and Collections know how to read and write themselves

To and from files in the filesystem

To and from URLs

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int main ( int argc, const char *argv[])

{

NSAutoreleasePool * pool = [[ NSAutoreleasePool alloc ] init ];

NSError *readError = nil ;

NSURL *url = [ NSURL URLWithString : @"http://www.apple.com" ];

NSString *htmlString = [ NSString stringWithContentsOfURL :url

NSError *writeError = nil ;

NSString *path = @"/tmp/Apple.html" ;

[htmlString writeToFile :path

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Categories

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Categories

Allow you to add methods to an existing class

Methods added to class at compile time (link phase)

Example: UIKit adds drawing methods to NSString

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@interface NSArray (MyExtensions) // In h file

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NSLog ( @"First object: %@" , [a firstObject ]);

NSLog ( @"Nicest guy: %@" , [a nicestGuy ]);

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Questions?

Tiêu đề	Objective-C and Java: a Comparison PART 1
Trường học	About Objects
Chuyên ngành	Objective-C and Java
Thể loại	developer–oriented training
Năm xuất bản	2009

Định dạng
Số trang	69
Dung lượng	3,04 MB