Objective-C and Java: a Comparison · Objective-C and Java: a Comparison PART 1 ... WebObjects (web app framework and ORM) ... Doesn't hurt to have more perspective on how client

About Objects

Objective-C and

Java: a

Comparison

PART 1

Developer–oriented training.

www.AboutObjects.com

http://www.AboutObjects.com

http://www.AboutObjects.com

© Copyright 2009 About Objects, Inc. All rights reserved worldwide.

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

2


About Objects

Reston Town Center (Accenture Building)

iPhone OS and MacOS X

Training

Development

Core Curriculum

ANSI C Programming

Objective-C Programming

Cocoa Programming Workshop

iPhone Programming Workshop

3

Overview


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)

5


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.)

6


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!

7

History

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

NeXT, Inc.'s NeXTCUBE

NEXTSTEP Timeline

1989 – NEXTSTEP 1.0

1992 – NEXTSTEP 486 for Intel

1994 – NeXT/Sun OpenStep spec.

1996 – OPENSTEP 4.0 released

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

What Apple Bought in 1996

From OpenStep to Mac

OS X

Mac OS X 10.0

March, 2001

Initial release of OS X

Port of OpenStep

+ Mac Toolbox APIs

+ 'Mac-like' UI tweaks

+ HFS+ file system

+ Mac OS 9 compatibility environment

+ Quartz rendering engine

Replacement for Display Postscript

+ Objective-C UI layer rebranded 'Cocoa'

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

Platforms


Comparing Platforms

Java

Almost everywhere

... except iPhone

Objective-C

Mac OS X

iPhone

17


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)

Foundation framework

UI framework

AppKit (Mac OS)

UIKit (iPhone OS)

18

iPhone SDK

Media

Core OS

Cocoa Touch

Core Services

iPhone SDK

Media

Core OS

Cocoa Touch

Core Services

Core Services

20

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

Media

iPhone SDK

Core OS

Cocoa Touch

Core Services

Media

iPhone SDK

Core OS

Cocoa Touch

Core Services

Media

Open GL ES

Core Graphics

Core Animation

Core Audio

iPhone SDK

Cocoa Touch

Media

Core OS

Core Services

iPhone SDK

Cocoa Touch

Media

Core OS

Core Services

Cocoa Touch

UIKit

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)

25


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)

26

Developer Tools

XCode

IDE for iPhone Projects

Build

Run (Simulator, device)

Debug

Source code management (SCM)

Documentation

Xcode

Automatically maintains build scripts

Displays logical groupings of files

No package paths

By default, groups not mapped to folder

structure

Resources

Automatically bundled with executable

Frameworks

Rough equivalent of JARs but at much coarser

granularity

Linked at compile time; no classpath needed

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

Instruments

Profiling

Performance Monitoring

Garage-Band 'multi-track' interface

Profiling

Performance Monitoring

Garage-Band 'multi-track' interface

Syntactic Differences


Message Syntax

Square brackets for message expressions

Java:

myString.toString()

Objective-C

[myString description]

33


Method Arguments

Arguments are delimited by colons

Java:

person.setFirstName("Fred");

Objective-C

[person setFirstName:@"Fred"];

34


Constants

Constant string object different from constant string

Java:

"Hello"

Objective-C

@"Hello" // String object

"Hello" // C string

35


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];

36


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

Inheritance is straight-forward

Memory allocation and initialization are separate steps

Java:

Employee emp = new Employee();

Objective-C

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

37


Prefix vs. Package Path

Obj-C language doesn't provide namespaces

Frameworks and libraries use prefixes by convention to avoid collisions

Java:

java.lang.String s = new String("hello");

Objective-C

NSString *s = [[NSString alloc] initWithString:"hi"];

38


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;

39


No Method Overloading

Runtime system looks up methods by name rather than signature

Makes introspection simpler and more efficient

Java:

manager.addEmployee(emp);

manager.addEmployee(emp, "Developer");

Objective-C

[manager addEmployee:emp];

[manager addEmployee:emp withTitle:@"Developer"];

40


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

41


Classes

Two separate files

Declared in .h file

Implemented in .m file

Compiler directives

@interface ... @end

@implementation ... @end

Curly braces

Instance variable section inside curly braces

Methods defined outside curly braces

42


#import <Foundation/Foundation.h>

@interface Person : NSObject

{ // Instance variables. Underscore prefix conventional, but not required.

int _age;

NSString *_firstName;}

// Instance methods. Getter methods cannot be prefixed with 'get'.

- (int)age;

- (void)setAge:(int age);

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

@end

Class Declaration

43

Anatomy of a Class Declaration


{

int _age;

NSString * _firstName;

}

...

@end

compiler directive

class we're declaring class it inherits from

name of instance variabledata type

Class Declaration: Methods


{

... // Instance variables go here

}

// Method declarations start here...

- (int)age;

- (void) setAge: (int)anAge;

...

@end

return type

method name

arg type

arg name


#import "Person.h"

@implementation Person

- (int)age {

return _age;}

- (void)setAge:(int age) {

_age = age;}

- (NSString *)firstName {

return firstName;}

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

// Note: Omits some memory management details... _firstName = firstName;

}

@end

Class Implementation

46


Visibility Modifiers

Compiler directives

@private

@protected

@public

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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{

// Visibility modifier. Applies to all ivars that follow.@private

// Private instance variables. NSString *_firstName;

NSNumber *_salary;

@protected // Protected instance variables.

int _age; }

// Instance methods.

...

@end

Visibility Modifiers

48

Memory Management


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

50


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.

51


// Deallocate anything we've retained or copied

- (void)dealloc{

[_firstName release]; [super dealloc];

}

- (NSString *)firstName{

return [[firstName copy] autorelease]; // Will be released after calling method completes

}

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

if (firstName != _firstName) // Avoid messing up the retain count {

[_firstName release]; // Release the previous one

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

}

Managing Reference Counts

52


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;

53


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

54



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

56


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"];

57


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];

58


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

59


NSDictionary

Similar to HashMap in Java

Mutable vs. immutable

Read and write itself as plist file

60


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

encoding:NSUTF8StringEncoding error:&readError];

if (readError) { NSLog(@"Unable to read URL: %@ due to error: %@", url, readError);

}

NSLog(@"HTML string: %@", htmlString);

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

[htmlString writeToFile:path atomically:YES

encoding:NSUTF8StringEncoding error:&writeError];

if (writeError) {

NSLog(@"Unable to write file at path: %@", path); }

[pool drain];

return 0;}

61

Categories


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

63


@interface NSArray (MyExtensions) // In .h file

- (id)firstObject;- (id)nicestGuy;

@end...

@implementation NSArray (MyExtensions) // In .m file- (id)firstObject

{ if ([self count] == 0)

return nil;

return [self objectAtIndex:0];}

- (id)nicestGuy

{ for (NSString *currStr in self) {

if ([currStr hasPrefix:@"J"]) return currStr;

}

return nil;}

@end

Example: Category on NSArray

64


#import <Foundation/Foundation.h>

#import "NSArray+MyExtensions.h"

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

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

NSArray *a = [NSArray arrayWithObjects:@"Fred", @"Joe", @"Bob", nil];

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

[pool drain];

return 0;}

Example: Using Category

65

Questions?

Documents

Objective-C and Java: a Comparison · Objective-C and Java: a Comparison PART 1 ... WebObjects (web app framework and ORM) ... Doesn't hurt to have more perspective on how client