Java J2SE

By Sandeep Desai (http://www.thedesai.net/)

See SCJP notes for Java Basics Source listings

Features

· Syntax Similar to C++

· Complies to platform independent byte code, so it can be run on any platform that has the Java Runtime Environment

· Execute using bytecode interpreter

· Garbage Collection

· Java Byte Code available on most platforms

· Provides API to do GUI, Web, XML, SQL Database Development and more

· Is a platform more than a language

· One public Class per file (can have many inner classes)

Books

· Thinking in Java (www.bruceeckel.com)

Websites

Major API’s

· Swing for doing GUI

· RMI (Invoke Remote Java Objects over Network)

· JDBC for working with Relational Databases (JDBC driver for each database vendor

· Servlets, Java Server Pages for Web development for writing Web Applications

· SAX and JDOM for XML Parsing

Java Development Kit

· Standard Edition (Java Compiler, Byte Code Interpreter Basic classes and Swing, RMI)

· Enterprise Edition (JDBC, Enterprise Java Beans, XML, SOAP etc) Requires an Server (container) for most APIs

· Micro Edition

· JavaDoc provides Help on API

· IDE’s provided, JDeveloper by Oracle, JBuilder by Borland, Eclipse Open source (www.eclipse.org)

Using JDK

· Download JDK from http://java.sun.com

· Install JDK

· Compile using javac e.g. javac Hello.java (creates Hello.class)

· Run java Hello

· If API is not part of JDK then requires setting CLASSPATH environment variable which points to Java Archive containing classes e.g to use the Servlet API requires that the Servlet API be downloaded e.g download servlet.jar and set CLASSPATH=c:\servlet.jar;c:\myjar.jar

Language Features

· OOP

· Single inheritance

· All objects inherit from java.lang.Object

· Multiple inheritance for interfaces

· Structured Exception Handling

· Data types are consistent across all platforms

· 32-bit

· Applet (run in a sandbox (secure mode) in a browser)

§ Can sign the applet to allow creating files etc on browser machine

· New 1.4 Features

§ Assertions

§ Logging API

· New 1.5 Features

§ Generics (similar to C++ templates)

§ enhanced for loop (Iterators)

§ autoboxing support

§ enumerations

Java Standard Edition API

Language
Collections
Files
Threads
Persistence
Sockets
RMI (Remote Method Invocation) Invoke Java object methods over the network
Swing (GUI)
JavaBeans
XML
Regular Expressions
Logging

Examples

// Hello.java

public class Hello {

public static void main(String[] args) {

System.out.println(“Hello World!”);

}

// To compile

<JAVA_HOME>/bin/javac Hello.java

// To run

<JAVA_HOME>/bin/java –cp . Hello

Use the –cp option for java or set the CLASSPATH to all the jar files and directories you want java to look in to find all your code. Put a ‘.’ to ensure java looks in current directory

set classpath=.;servlet.jar;c:\foo

javac	Compile java program
java	Run Java Program
javaw	Run Java program with launching a DOS window
javadoc	Generate HTML JavaDoc from source code

jar	Create Java Archive Files (like a tar file or zip file containing many Java classes)
jdb	Command line Java Debugger

Java Primitive Data types

Primitive type	Size	Minimum	Maximum	Wrapper
Boolean				Boolean
char	16-bit	Unicode 0	Unicode 2^16-1	Character
byte	8-bit	-128	+127	Byte
short	16-bit	-2¹⁵	+2¹⁵+1	Short
int	32-bit	-2³¹	+2³¹-1	Integer
long	64-bit	-2⁶³	+2⁶³-1	Long
float	32-bit	IEEE754	IEEE754	Float
double	64-bit	IEEE754	IEEE754	Double
void				void

Operator precendence

Mnemonic	Operator Type	Operators
Ulcer	Unary	+ - ++ --
Addicts	Arithmetic and Shift	* / % + - << >>
Really	Relational	> < <= >= == !=
Like	Logical and bitwise	&& \|\| & \| ^
C	Conditional (ternary)	a > b ? c : d
A lot	Assignment	= += *= %= /=

Wrapper conversion

primitive xxxValue() to convert Wraper to primitive

primitive parseXxx(String) to convert String to a primitive

Wrapper valueOf(String) to convert a String to Wrapper

Method s=static n=NFE Exception	Boolean	Byte	Characater	Double	Float	Integer	Long	Short
byteValue		x		x	x	x	x	x
doubleValue		x		x	x	x	x	x
floatValue		x		x	x	x	x	x
intValue		x		x	x	x	x	x
longValue		x		x	x	x	x	x
shortValue		x		x	x	x	x	x

parseXxx s,n		x		x	x	x	x	x
parseXxx s,n (with radix)		x				x	x	x

valueOf s,n	x	x		x	x	x	x	x
valueOf s,n (with radix)		x				x	x	x

toString	x	x	x	x	x	x	x	x
toString s (primitive)	x	x	x	x	x	x	x	x
toString s (primitive, radix)						x	x

toBinaryString s						x	x
toHexString s						x	x
toOctalString s						x	x

Core Java

File	Description
AssertApp.java	// 1.4 feature public class AssertApp { public static void main(String[] args) { boolean s = false; assert s : “s failed”; } } javac –source 1.4 AssertApp.java java –ea:AssertApp –cp . AssertApp
AppProperties.java	//work with Properties which can be loaded from file e.g Test.properties //Property1=value1 //Property2=value2 import java.util.Properties; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.PrintStream; public class AppProperties { public Properties m_properties; private String m_propFileName; public AppProperties(String propFileName) { m_propFileName = propFileName; m_properties = new Properties(); } public void loadProperties() throws Exception { try { FileInputStream propInputStream = new FileInputStream(m_propFileName); m_properties.load(propInputStream); propInputStream.close(); } catch (Exception e) { throw e; } } public void saveProperties() throws Exception { try { FileOutputStream propOutputStream = new FileOutputStream(m_propFileName); m_properties.save(propOutputStream , ""); propOutputStream.close(); } catch (Exception e) { throw e; } } public void list(PrintStream p) { m_properties.list(p); } public String getProperty(String propertyName) { return m_properties.getProperty(propertyName); } public void setProperty( String propertyName, String propertyValue) { m_properties.put(propertyName, propertyValue); } }
Areflect.java	uses the Reflection API that allows you to dynamically load classes and browse the class info such as methods, members and invoke them
ArrayList.java	uses the ArrayList Collection import java.util.ArrayList; ArrayList a = new ArrayList(); a.add("hello"); a.add("world"); String[] as = new String[a.size()]; a.toArray(as); for (int i = 0; i < as.length; ++i) System.out.println(as[i]);
Beep.java	java.awt.Frame f = new java.awt.Frame(); f.getToolkit().beep(); Toolkit.getDefaultToolkit().beep();
EAIORServer.java
Exec.java	Launches an appliction try { Runtime rt = Runtime.getRuntime(); String s[] = new String[2]; s[0] = "c:\\winnt\\notepad.exe"; s[1] = "c:\\junk\\todo.txt"; Process p = rt.exec(s); } catch (Exception e) { System.out.println(e); }
File.java
FileDialog.java	Show AWT Open File Dialog
FileRead.java	Read Text files line by line
GetLocalHost.java	java.net.InetAddress localhost = java.net.InetAddress.getLocalHost();

RMI

define interface and use rmic to generate client stubs and server skeleton

JVM will marshall and umarshall for RMI communication

Run rmiregistry to register server object

Lookup sever object in rmiregistry

each method must declare java.rmi.RemoteException in its throw clause

Setting Locales

java.util.Locale defaultLocale = Locale.getDefault();

Locale newLocale = new Locale(“en”, “us”);

Locale.setDefault(newLocale);

... some code...

Locale.getDefault(defaultLocale);

Reading a japanese file

java.io.FileInputStream fis =

new FileInputStream(getServletContext().getRealPath("/HelloWorld.ISO-2022-JP"));

//new FileInputStream(req.getRealPath("/HelloWorld.ISO-2022-JP"));

InputStreamReader isr = new InputStreamReader(fis, "ISO-2022-JP");

BufferedReader reader = new BufferedReader(isr);

String line = null;

while ((line = reader.readLine()) != null) {

System.out.println(line);

Converting string to japanese

try {

  ustr = new String(str.getBytes("SJIS"),"8859_1");

  } catch (IOException e){ System.err.println("IO error: str="+str);

Java Servlet 2^nd Edition by Jason Hunter and William Crawford has good infomation and code for Internationalization in Java

Java Thread

class PrimeRun implements Runnable {

  long minPrime;

  PrimeRun(long minPrime) { this.minPrime = minPrime; }

  public void run() { // compute primes larger than minPrime   }

//The following code would then create a thread and start it running:

PrimeRun p = new PrimeRun(143);

new Thread(p).start();

Apache Regular Expression

import org.apache.regexp.RE;

import org.apache.regexp.RECompiler;

public class regtest {

public static void main(String[] args) {

try {

String match = args[0];

String expr = "^S";

RE r = new RE(expr);

//RECompiler compiler = new RECompiler();

//r.setProgram(compiler.compile(expr));

if (r.match(match))

System.out.println("match=" + match);

else System.out.println("no match=" + match);

}

catch (Exception e) {

System.out.println(e);

}

Java Webstart (JNLP)

It is installed on a client machine and allows you to download Java Applications over the web and run it locally. It can be run as a browser plugin or a standalone application. It caches the application and updates the jar files if they change. It is an implementation of the JNLP (Java Network Launch Protocol)

Steps to create a certificate

· keytool –genkey –keystore myKeystore –alias myself

· keytool –selfcert –alias myself –keystore myKeystore

· keytools –list –keystore myKeystore

Sign the jar file with the following command

· jarsigner –keystore myKeystore test.jar myself

Create a jnlp file and. Copy the jnlp file and the jar files to a Web server directory.

<?xml version="1.0" encoding="utf-8"?>

<jnlp

spec="1.0+"

codebase="http://sbdesai-pc2:7778/"

href="awm.jnlp">

<information>

<title>Analytic Workspace Manager</title>

<vendor>Oracle Corp.</vendor>

<homepage href="docs/help.html"/>

<description>Analytic Workspace Manager</description>

<description kind="short">AWM 9.2.0.3.1</description>

<icon href="awm.jpg"/>

<icon kind="splash" href="awm.gif"/>

<offline-allowed/>

</information>

<security>

<all-permissions/>

</security>

<resources>

<j2se version="1.4+" initial-heap-size="512m"/>

<jar href="awm.jar"/>

<jar href="classes12.jar"/>

</resources>

<application-desc main-class="oracle.olap.awm.app.AwmApp"/>

</jnlp>

Netx (Network Execute) is an open source implementation of JNLP download from http://jnlp.sourceforge.net/netx

java -jar netx-0.5.jar -jnlp http://localhost/awm.jnlp

JDBC

JDBC 2.0 Compliance requires

Data Source support

Java Transaction API (JTA) and XA connection support, XA is used for distributed transaction support

Connection Pooling

Complete Data type support

Oracle has 3 types of JDBC driver, thick driver (requires Oracle Client) thin driver

e.g Oracle JDBC Url, note username/password is optional

· Thin JDBC jdbc:oracle:thin:scott/tiger@localhost:1521:ORCL

· Thick JDBC jdbc:oracle:oci8:scott/tiger@orcl

· Java in Database connection jdbc:oracle:kprb

// Code to insert a japanese unicode string row into a table

// create table test (col as varchar2(100));

DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());

Connection conn = DriverManager.getConnection(“jdbc:oracle:thin:@localhost:1521:orcl";, "scott", "tiger");

conn.setAutoCommit(true);

String query = "insert into test values (?)";

PreparedStatement pstmt = null;

pstmt = conn.prepareStatement(query);

String jpstr = "\u4eca\u65e5";

String dbstr = toUTF8String(jpstr);

pstmt.setString(1, jpstr);

pstmt.executeUpdate();

conn.close();

Java and Log4J (Apache API for Logging in Java)

Loggers: named entities and have a hierarchy based on names. (name hierarchy is similar to package names)

Appenders: are output destinations can be console, file or user implementable. Multiple appenders can be set for a Logger. Loggers will write to all appenders for the current Logger and to all the appenders set for the ancestors.

Layouts is responsible for formatting the logging request according to the user's wishes

Chainsaw Massacre is a GUI viewer for log messages

Loggers have level, the logged output is logged for level >= level set by user

Logger printing methods are debug(), info(), warn(), error(), fatal() and log().

For the standard levels, we have DEBUG < INFO < WARN < ERROR < FATAL.

package com.foo;

import org.apache.log4j.Logger;

import org.apache.log4j.BasicConfigurator;

public class MyApp {

public static void main(String[] args) {

// Set up a simple configuration that logs on the console.

BasicConfigurator.configure();

Logger logger = Logger.getLogger("com.foo");

logger.setLevel(Level.INFO);

logger.warn("Low fuel level.");

logger.debug("Starting search for nearest gas station.");

Logger barlogger = Logger.getLogger("com.foo.Bar");

barlogger.info("Located nearest gas station.");

barlogger.debug("Exiting gas station search");

}

output will be

Low fuel level

Located nearest gas station

Logger.addAppender(new org.apache.log4j.ConsoleAppender());

For example, the PatternLayout with the conversion pattern "%r [%t] %-5p %c - %m%n" will output something akin to:

176 [main] INFO org.foo.Bar - Located nearest gas station

The first field is the number of milliseconds elapsed since the start of the program. The second field is the thread making the log request. The third field is the level of the log statement. The fourth field is the name of the logger associated with the log request. The text after the '-' is the message of the statement.

// BasicConfigurator replaced with PropertyConfigurator.

PropertyConfigurator.configure(“MYAPP.PROPERTIES”);

e.g. MYAPP.PROPERTIES

# Set root logger level to DEBUG and its only appender to A1.

log4j.rootLogger=DEBUG, A1

# A1 is set to be a ConsoleAppender.

log4j.appender.A1=org.apache.log4j.ConsoleAppender

# A1 uses PatternLayout.

log4j.appender.A1.layout=org.apache.log4j.PatternLayout

log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

# Print only messages of level WARN or above in the package com.foo.

log4j.logger.com.foo=WARN

Swing

Swing provides all the UI Controls for building a Java GUI. It extends AWT, (Abstract Windowing Toolkit) which is the older GUI API

import javax.swing.*

abstract class JTextComponent base class for Swing text components

setEditable(boolean)

setText(String)

String str = getText();

// JTextArea extends JTextComponent // multiline Text Field

jtf = new JTextArea();

setRows(int rows)

setLineWrap(true);

setWrapStyleWord(true); // wrap on word boundaries

// JCheckBox extends JtoggleButton extends AbstractButton // Check box

AbstractButton.getModel().isSelected();

// JComboBox extends JComponent // text field with drop down list

JComboBox jc = new JComboBox();

jc.addItem(“Item1”);

jc.addItem(“Item2”);

String str = (String) jc.getSelectedItem();

jc.setSelectedItem(“Item2”);

DefaultComboBoxModel dc = new DefaultComboBoxModel();

dc.removeAllElements();

dc.addElement(“Hola”);

JComboBox jcm = new JComboBox(dc);

jcm.addActionListener(new ActionListener()

{

public void actionPerformed(ActionEvent e)

{

JComboBox cb = (JComboBox) e.getSource();

String si = cg.getSelectedItem();

}

});

// JList extends JComponent

DefaultListModel dlm = new DefaultListModel();

dlm.addElement(“test”);

JList jl = new JList(dlm);

JTextField extends JTextComponent // single line text field

JTextFeld tf = new JTextField();

tf.setBorder(javax.swing.BorderFactory.createLoweredBevelBorder());

String val = tf.getText();

tf.getDocument.addDocumentListener(new DocumentListener()

        public void changedUpdate(DocumentEvent e) { }

        public void insertUpdate(DocumentEvent e) {}

        public void removeUpdate(DocumentEvent e) {}

JLabel label = new Jlabel(“Enter Data”);

label.setLabelFor(tf); // Accessibility

label.setMnemonicChar(‘E’); // Accessibility

label.setOpaque(true);

label.setBackgroundColor(Color.white);

JRadioButton rb1 = new JRadioButton(“Option1”);

JRadioButton rb2 = new JRadioButton(“Option2”);

ButtonGroup bg = new ButtonGroup();

bg.add(rb1);

bg.add(rb2);

rb1.getModel().isSelected();

rb1.getModel().setSelected(true);

JFrame extends java.awt.Frame // top level Window

addWindowFocusListener(new WindowAdapter()) {

public void windowClosing(WindowEvent e) { System.exit(0); }

public void windowActivated WindowEvent e)

public void windowGainedFocus (WindowEvent e)

…