meljun cortes java lecture java5 new features

8/13/2019 MELJUN CORTES JAVA Lecture Java5 New Features

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New Java 5FeaturesJava Fundamentals and Object-Oriented

Programming

The Complete Java Boot Camp

MELJUN CORTES

MELJUN CORTES


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The Big Stuff Generics

Enumerations

New concurrency constructs

New interfaces

Autoboxing

New loop for/in


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Less Big Stuff

Static imports

varargs

System.lang.Formatter

Annotations

JVM monitoring and control


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Generics Java Generics were stron gly d r iven by

desire for less f idd ly Col lect ions

programming.

Like C++ temp lates, prov ide com pile-t ime

reso lut ion of datatype abstract ions that

preserve type safety and el im inate need fo r

cast ing.


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GenericsCan emplo y generics in classes, interfaces

and method s.

Unlik e C++ temp lates, Generics are more

than a clever macro processor: Java

compiler keeps track o f generics in ternally,

and uses same class f i le for al l instances.


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Six core collections interfacesare synchronization wrappers:

Collectionabstract generic

class List

Set, SortedSet

Map, SortedMap

Non-generic collections classes(HashMap, etc.) stillavailable, of

course.

Generic Collections


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Java 1.4 :

Simplify Collections Use

Java 1.5:

LinkedList list = new LinkedList();list.add(new Integer(1));Integer num = (Integer) list.get(0);

LinkedList list= new LinkedList();

list.add(new Integer(1));Integer num = list.get(0);


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Original

HashMap celebrityCrashers = new HashMap();celebrityCrashers.put(

new Date( 10/05/2005 ),new String( Lindsay Lohan ) );

Date key = new Date( "10/1/2005" );if ( celebrityCrashers.containsKey( key ) ){

System.out.println("On " + key + , +(String) celebrityCrashers.get( key )+ crashed a vehicle.");

}


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Hot and Crispy

Map celebrityCrashers= new HashMap();

celebrityCrashers.put( new Date(10/05/2005),new String( Lindsay Lohan ) );

Date key = new Date("10/05/2005");if ( celebrityCrashers.containsKey( key ) ) {

System.out.printf(

"On %tc, %d crashed a vehicle%n,key, celebrityCrashers.get( key ) );


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Defining Generics

Classes

Interfaces

Methods

class LinkedList implements List {// implementation

}

interface List {void add(E x);Iterator iterator();

}

void printCollection(Collection c) {for(Object o:c) {

System.out.println(o);}

}


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Wildcards ? extends Typea family of Type

subtypes

? super Typea family of Typesupertypes

?- the set of all Types, or anypublic static


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Enumerations In Java 1.4: 'type safe enum' design pattern:

// This class implements Serializable to preserve valid equality// tests using == after deserialization.

public final class PowerState implements java.io.Serializeable {private transient final String fName;private static int fNextOrdinal = 1;private final int fOrdinal = fNextOrdinal++;

private PowerState(String name) {this.fName = name;

}

public static final PowerState ON = new PowerState("ON");public static final PowerState OFF = new PowerState("OFF");

public String toString() {return fName;

}

private static final PowerState[] fValues = {ON, OFF};

private Object readResolve () throws java.io.ObjectStreamException{return fValues[fOrdinal];

}}


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Enumerations A bit more concise in Java 5:

public enum PowerState {ON, OFF};

Enum classes:

declare methods values(), valueOf(String)

implement Comparable, Serializeable

override toString(), equals(), hashCode(), compareTo()


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java util concurrent New package that supports concurrent

programming

Executor interface executes a Runnable

ThreadPoolExecutor class allows creationof single, fixed and cached thread pools

Executor also executes Callable objects.

Unlike Runnable, Callable returns a resultand can throw exceptions


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Autoboxing Easier conversion between primative and

reference types

// Java 1.4

List numbers = new ArrayList();numbers.add(new Integer(-1));int i = ((Integer)numbers.get(0)).intValue();

// Java 5

List numbers = new ArrayList();numbers.add(-1); // Box int to Integerint i = numbers.get(0); // Unbox Integer to int


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Static Imports

Langauge support makes it easier to importstatic members from another class. Nomore BigBagOf Constants interfaces.

import static java.lang.Math.*;

...

int x = round(4.5f);...


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Enhanced for oopCollection temperatures

= new LinkedHashSet();

temperatures.add(105);temperatures.add(92);temperatures.add(7);

for(Integer aTemp : temperatures) {System.out.println("This temperature is " + aTemp);

}

Hides the loop counter or Iterator....

...but therefore can't be used when yourcode needs the counter or Iterator.


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Variable Argument List

public int min(int first, int... rest) {

int min = first;

for(int next: rest){if (next < min) min = next;

}return min;

}

varargs mechanism allows variable length argumentlists.


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java.util.Formatter Class

Provides control of string formatting akin toC's printf()

Utilizes a format string and formatspecifiers

Unlike C format strings, note use of % assole format specifier. No backslashes, such

as \nSystem.out.printf(%s crashed on %tc%n,

celebName, crashDate);


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Annotations Let you associate metadata with program

elements

Annotation name/value pairs accessible

through Reflection API

Greatest utility is to tools, such as codeanalyzers and IDEs. JDK includes apt too lthat pro vides framework fo r annotat ion

process ing tools .


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Annotations Most useful annotation to programmer:@Override

interface Driver {//...

int getDrivingSkillsIndex();}

public class Celebrity implements Driver {//...

/**

* The @Override annotation will let the compiler* catch the misspelled getDrivinSkillsIndex().*/@Override getDrivinSkillsIndex() { return 0; }

//...


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Annotations

Next most useful annotations toprogrammers:@Deprecated, @SuppressWarnings

@Deprecated public class BuggyWhip{ ... }

//...

// @SuppressWarnings selectively turns off javac warnings// raised by use of the -Xlint option

@SuppressWarnings({fallthrough})public void iUseSloppySwitchCoding { ... };


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AnnotationsYou can define your own (e.g., to supplant

javadoc tags, or annotate for codemanagement practices)

See Chapter 4 of Java In A Nutshell


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Monitoring & Management

JMX API (javax.management) provides remotemonitoring and management of applications

java.lang.management uses JMX to define

MXBean interfaces for monitoring and managinga running JVM

MXBean interface lets you monitor classloadings, compilation times, garbagecollections, memory, runtime configuration andthread info.

MXBean also provides for granting of JVMmonitoring and control permission


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Monitoring & Management

java.lang.instrument defines the API to defineagents that instrument a JVM by transforming classfiles to add profiling support, code coveragetesting

Instrumentation agent classes define premain()method, which is cal led dur ing startup before main()

for each agent class speci f ied on the Java

interpreter command l ine

Ins trumentat ion object can registerClassFi leTrans former ob jects to rewri te class f i le

by te codes as they're loaded.


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References & Credits

Sun J2SE 5 tutorialhttp://java.sun.com/developer/technicalArticles/J2SE/generics/

Java 5 In A Nutshell (O'Reilly's Nutshell Series)

A quick tour 'round Java 5http://www.clanproductions.com/java5.html

Type Safe Enumerationshttp://www.javapractices.com/Topic1.cjp#Legacy
http://java.sun.com/developer/technicalArticles/J2SE/generics/http://www.clanproductions.com/java5.htmlhttp://www.clanproductions.com/java5.htmlhttp://www.clanproductions.com/java5.htmlhttp://java.sun.com/developer/technicalArticles/J2SE/generics/http://java.sun.com/developer/technicalArticles/J2SE/generics/

meljun cortes java lecture java5 new features

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