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1.01.0LibrariesLibraries

TechnicalTechnicalOverviewOverview

Jonni KanervaJonni KanervaFrank YellinFrank Yellin

JavaSoftJavaSoft

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Outline

Introduction Functionality in the 1.0 Libraries

Distributed design of the Java platform Instructive oddities

Design patterns Extensibility

Wrapup

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Approach

Yes: explore the universe General principles and overview

Instructive oddballs and treats

Larger-scale patterns

No: even-handed skim survey

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Background Reading

The Java Application ProgrammingInterface, Vols. 1 & 2

James Gosling, Frank Yellin, The Java TeamAddison-Wesley, 1996

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Central Themes

Functionality What can you do with 1.0 java.*?

Design

The pieces

How they fit together and cooperate

Extensibility

java.* provides a simple, ubiquitous,

extensible base for your programs.

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API Slogans

Simplicity is power,accuracy is leverage

Provide partial designs, ready to be

woven together

The simple should be simple,

the complex should be possible

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API Goals

Function Overall scope is good

Important problems are solvable

Partition

Divide and conquer complexity

Pieces are understandable

Pieces are changeable

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API Goals (cont.)

Names Simple, direct, systematic

Reduce chances for misunderstanding

Extensible

Easy to specialize

Easy to connect

Platform independent

Implementable

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Good API = ???

Learnable Easy to learn, easy to remember

Usable

Easy to code to, easy to build tools on

Flexible

Allow different solutions and solution styles

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Next

Introduction Functionality in the 1.0 Libraries

Distributed design of the Java platform Instructive oddities

Design patterns Extensibility

Wrapup

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Functionality

in the 1.0 Libraries

Javacompatible library = Java package Classes

Interfaces

Subpackages

Functionality spread through 8 packages

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Packages in the 1.0 API

java.lang: core language support java.io: input/output streams, data types

java.net: networking support

java.util: HashTable, StringTokenizer

java.awt: cross-platform window toolkit

java.awt.peer: interfaces to native GUI

java.awt.image: image processing

java.applet: applets and applet contexts

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21 classes, 2 interfaces, 40 excep/errors Class wrappers for primitive data types:

Boolean, Integer, Double

Classes for core language concepts:

String, Thread, Object

Access to system resources:

Process, Runtime, System,

Imported by every Java-powered program

Package java.lang

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Package java.io

23 classes, 3 interfaces, 5 sections Byte-oriented stream abstraction for

input and output

Mix and match filtering

Cross-platform file abstraction

Stream tokenizer

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Package java.net

11 classes, 3 interfaces, 5 exceptions URLs

URL connections Sockets

Internet addresses

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Package java.util

10 classes, 2 interfaces, 2 exceptions Generic utilities:

Vector, HashTable, Stack, Enumeration,

BitSet, StringTokenizer

Date

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Package java.awt

42 classes, 2 interfaces, 1 exception, 1 error GUI elements:

Button, TextField, Window, Menu,

Event handling

Fonts and font metrics

Graphics

Colors

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Package java.awt.peer

0 classes, 22 interfaces Interfaces for communicating with

native GUI elements:

ButtonPeer, TextFieldPeer,

Decouples AWT classes from platform-

specific toolkit implementations

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Package java.awt.image

9 classes, 3 interfaces Image creation

Image filters Color mapping

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Package java.applet

1 class, 3 interfaces The Applet class

Applet audio and images Applet context:

Applet-browser relationship

Inter-applet communication

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Distributed Design of

the Java Platform

Java platform = runtime + language + classes

java.* standard API

On all Java-compatible platforms

Write once, compile once, run everywhere

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Classes Complement the

Language and Runtime

java.* classes are integrated with corelanguage mechanisms:

Primitive data types

Operators

Class and interface membership

Control flow Runtime and environment

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Primitive Data Types

and java.* Classes

boolean: Boolean char: Character

int, long: Integer, Long

float, double: Float, Double

Double d = new Double(3.14159);

double simplePi = d.doubleValue();

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Operators and

java.* Classes

Language: + Classes: String, StringBuffer

String s = a + b;String s = new

StringBuffer().append(a).append(b).toString();

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Class/Interface Types

and java.* Classes

Language: class, interface, implements, extends, instanceof

Classes: Class, Object

interface Fooable { public void fooIt(); }

class Foo implements Fooable { public void fooIt() {} }

Fooable obj = new Foo();obj.getClass() ==> class Foo

obj.getClass().getSuperclass().isInterface() ==> false

Class.forName("Fooable").isInterface() ==> true

M l i h di d

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Multithreading and

java.* classes

Language: synchronized (methods and blocks)

Classes:

Thread, ThreadGroup,

Object: waitand notifymethods

Thread thread1, thread2; Runnable r;

thread1 = new Thread(r);

thread2 = new Thread(r);

thread1.start(); thread2.start();

C l Fl d

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Control Flow and

java.* Classes

Language: try, catch, finally, throws

Classes:

Throwable, Error, Exception

try {

sleep(500);} catch (InterruptedException e) {

System.out.println(e = + e);

}

R ti /E i t

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Runtime/Environment

and java.* Classes

Runtime/Environment: Object allocation, security, garbage

collection

Classes:

Class, ClassLoader, Object

Runtime, System, SecurityManager

String s1 = (String)Hello.getClass().newInstance();

String s2 = System.getProperty(java.version);

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Recap

Integrated Java-compatible platformincludes java.* classes

Standard on all Java-compatible systems

java.lang.* is the core of the core

Most tightly integrated

Imported automatically

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Instructive Oddities

Typical class in java.*: Public, concrete, subclassable

Has instance methods, instance variables

Variety is the spice of life: A classy class

A very protected class A very abstract class

An abstract but not abstract class

A half class, half language primitive

j l g M th

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java.lang.Math

A Classy Class

Two numerical constants: Math.E, Math.PI

Range of standard math functions

All as class methods:public static double tan(double a)

Declared as final no subclasses No constructor

No instances

java lang ClassLoader

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java.lang.ClassLoader

A Very Protected Class

Key class for security: Methods and constructor accessible only from

your own subclass

Only one method can/must be overridden

protected ClassLoader()

protected final void resolveClass(Class c)protected final Class findSystemClass (String name)

protected final Class defineClass(byte[] data, int offset, int length)

protected abstract Class loadClass (String name, boolean resolve)

java lang Number

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java.lang.Number

A Very Abstract Class

Abstract superclass for number objects: Integer, Long, Float, Double

public abstract class Number { public abstract int intValue();

public abstract long longValue();

public abstract float floatValue();

public abstract double doubleValue();}

java awt Component

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java.awt.Component

Abstract or Not?

Contains no abstract methods Declared as an abstract class

Cannot be instantiated

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Array Half Class

Not in any package One final instance variable: length

Cannot be extended (subclassed)

Superclass is Object

Inherits methods from Object

(new int[5]).getClass().getSuperclass() ==> java.lang.Object

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Design Patterns

Weaving partial designs together Interactions of classes, interfaces, and

instances

Design units within larger picture

Tool for understanding

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Recommended Reading

Design Patterns: Elements of ReusableObject-Oriented Software

Gamma, Helm, Johnson, VlissidesAddison-Wesley, 1995

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Decorator The Pattern

Extend functionality of an object Not statically through subclassing

By wrapping it in another object, a decorator

Decorators interface is superset of

decoratees

Decorator forwards some requests todecoratee

Decorator Example:

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Decorator Example:

java.io Input And Output

Byte-oriented stream input and output Base classes are InputStream, OutputStream

Mix and match filtering:

Filter, Buffered, Data, LineNumber...

FilterInputStream.read():

Invokes read() on the decoratee InputStream:

return in.read();

Buffered Numbered

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Buffered, Numbered,

Line Input from a File

FileInputStream in1 = new FileInputStream(data.txt); BufferedInputStream in2 = new BufferedInputStream(in1);

LineNumberInputStream in3 = new LineNumberInputStream(in2);

DataInputStream in4 = new DataInputStream(in3);

String line; while ((line = in4.readLine()) != null) {

System.out.println(in3.getLineNumber() + : + line);

}

in4.close();

data.txt readLine()File Buffer Line Data

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Composite The Pattern

Compose objects into tree structures to represent

part-whole hierarchies. Composite lets clients treatindividual objects and compositions of objectsuniformly. (p. 163)

Composite Example: java awt

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Composite Example: java.awt

Component and Container

Abstract superclass: Component

Presence on screen, size, location

Receive, handle, and deliver events

Most AWT GUI elements inherit fromComponent

Container is subclass of Component

Contains a group of components (children)

Can create arbitrarily deep containment

hierarchy

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Component-Container Trees

Frame

Label

Panel

Button Button

BorderLayout

FlowLayout

Frame

LabelPanel

Button Button

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Strategy The Pattern

Define a family of algorithms, encapsulate each

one, and make them interchangeable. Strategy letsthe algorithm vary independently from the clientsthat use it. (p.315)

Strategy Example:

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Strategy Example:

java.awt.LayoutManager

How to place components in a container

Dynamic constraint-based layout

Interface with 5 methods:

Add, remove, layout, minimum,

preferred

java.awt package provides: BorderLayout, CardLayout, FlowLayout,

GridLayout, GridBagLayout

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Flow and Border Layouts

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Bridge The Pattern

Decouple an abstraction from its implementation

so that the two can vary independently. (p. 151)

Bridge Example: java.awt

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g p j

Components and Peers

MFrame

MLabelMPanel

MButton MButton

Frame

LabelPanel

Button Button

Java AWT Motif Peers

Chain of Responsibility

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p y

The Pattern

Avoid coupling the sender of a request to its

receiver by giving more than one object a chance tohandle the request. Chain the receiving objects andpass the request along the chain until an object

handles it. (p. 223)

Chain of Responsibility

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p y

Example: AWT Events

EventEvent

Frame

LabelPanel

Button Button

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Extensibility

Extensibility pervades java.*

Subclass a concrete class

Subclass an abstract class, prespecified holes

Implement an interface

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Extend a Concrete Class

Six favorite concrete classes to extend

java.applet.Applet: custom applets

java.awt.Canvas: custom GUI components

java.awt.Panel: custom GUI containers

java.awt.Frame: custom top-level windows

java.lang.Thread: custom execution thread ???

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Extend an Abstract Class

extend java.io.InputStream

Implement: read()

extend java.lang.ClassLoader

Implement: loadClass(String, boolean)

extend java.awt.Graphics

29 abstract methods to implement

Example: write your own PSGraphics class

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Implement an Interface

As part of the classs duties

java.lang.Runnable in an Applet subclass

As all of the classs duties

java.awt.LayoutManager

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Upcoming Extensions

Security: digital certificates, authentication

Multi-media: 2-D, 3-D, video, audio

JDBC: database access and connectivity

Remote Objects: remote method invocation

Persistent Objects

Electronic Commerce

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Wrapup 1.0 java.*

Simple, ubiquitous, extensible base foryour programs:

Integrated with language

Available on all Java-compatible platforms

Goals and progress:

Learnable, usable, flexible, platformindependent, implementable