rdata.work

Java

JDK

select version of JAVA to use (Oracle or OpenJDK)
$ sudo update-alternatives --config java

select java using alternatives

install to /usr/java/latest
$ sudo rpm -i jdk-8u[xxx]-linux-x64.rpm
install openjdk sources
$ sudo dnf install java-1.8.0-openjdk-src.x86_64
add environment variable (/etc/environment or ~/.profile)
`JDK_HOME=”/usr/lib/jvm/java-openjdk”

OpenJFX

get sources using mercurial
$ hg clone http://hg.openjdk.java.net/openjfx/8u-dev/rt

IDEs

NetBeans IDE 8.1 (requires JDK installation)

make the installer files executable
$ chmod +x netbeans-8.1-javaee-linux.sh
run the installer
$ ./netbeans-8.1-javaee-linux.sh
JDK for the NetBeans IDE: /usr/java/latest
uninstall run the uninstall.sh file in the IDE installation directory
$ cd ~/netbeans-8.1
$ ./uninstall.sh
Add GlassFish Server as a Server in NetBeans IDE
Tools -> Server -> Add Server...

screenshot netbeans glassfish server

Install First Cup Tutorial in NetBeans

  • open tab Windows -> Services (Ctrl+5)
  • expands Servers, right-click GlassFish Server 4.1.1, select View Domain Update Center and install if required
  • right-click GlassFish Server 4.1.1, select Start; after it started, select View Domain Admin Console
  • a new browser window opens and after GlassFish server has been initialized, click Update Tool in Common Tasks context menu
  • select javaee-firstcup-tutorial for installation in Available Add-Ons, click install
  • this will create the project files at ~/glassfish-4.1.1/docs/firstcup

Library Path

$ cat GetSystemProperty.java
import java.util.Properties;
import java.util.Enumeration;

public class GetSystemProperty {
  public static void main(String args[]) {
    if( args.length == 0 ) {
      Properties p = System.getProperties();
      Enumeration keys = p.keys();
      while (keys.hasMoreElements()) {
        String key = (String)keys.nextElement();
        String value = (String)p.get(key);
        System.out.println(key + " : " + value);
      }
    }
    else {
      for (String key: args) {
        System.out.println(System.getProperty( key ));
      }
    }
  }
}
$ javac GetSystemProperty.java
$ java GetSystemProperty java.library.path
$ /usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib

Build from command line

with structure src/pkg/Temp.java

compile
xps13@xps13 pkg]$ javac Temp.java
run
[xps13@xps13 src]$ java pkg.Temp

Oracle Java

Learn

Java EE

Tutorial

This tutorial is a guide to developing enterprise applications for the Java Platform, Enterprise Edition 6 (Java EE 6) using GlassFish Server Open Source Edition.

Windows

Test Java version

  • java -version

Edit environment variables

  • JAVA_HOME=C:\Program Files\Java\jre1.8.0_51

GlassFish

Alternative application servers

  • WebLogic
  • WebSphere
  • JBoss
  • Tomcat (does not support .EAR files - compare .WAR)

JavaServer Pages (JSP)

JavaServer Faces (JSF)

JavaServer Faces technology establishes the standard for building server-side user interfaces.

Unified Expression Language (EL)

Unified EL integrates the expression languages defined by JSP 2.0 and JSF 1.1. Thanks to the Unified EL, JSTL tags, such as the JSTL iteration tags, can now be used with JSF components in an intuitive way.

Build Tools

Apache Maven

find maven version
mvn -version

Apache Ant

Compile Java source code

install on Fedora 22
sudo dnf install ant

Example: Build SDMX library

navigate to root directory
cd ~/Dropbox/GitHub/SDMX/JAVA
clean the subtree
ant clean
compile the code
ant compile
build and install the java library (this will also copy the generated jar file in the dist subdir and in the correct library directories of each connector)
ant dist

Command line usage

navigate to root directory
cd ~/Dropbox/GitHub/SDMX/JAVA
run query
java -classpath dist/lib/SDMX.jar it.bancaditalia.oss.sdmx.util.GetTimeSeries ECB EXR.A.USD.EUR.SP00.A
open the SDMX Helper tool
java -jar dist/lib/SDMX.jar
run with different java version
$JAVA_HOME/bin/java -classpath dist/lib/SDMX.jar it.bancaditalia.oss.sdmx.util.GetTimeSeries ECB EXR.A.USD.EUR.SP00.A

WebJars

WebJars are client-side web libraries (e.g. jQuery & Bootstrap) packaged into JAR (Java Archive) files.

  • Explicitly and easily manage the client-side dependencies in JVM-based web applications
  • Use JVM-based build tools (e.g. Maven, Gradle, sbt, …) to download your client-side dependencies
  • Know which client-side dependencies you are using
  • Transitive dependencies are automatically resolved and optionally loaded via RequireJS
  • Deployed on Maven Central

OCA

  • OCA Oracle Certified Associate Java SE 8 Programmer I Study Guide Exam 1Z0-808

Self-assessment

What is the result of the following class? (Choose all that apply)

1: public class _C {
2: private static int $;
3: public static void main(String[] main) {
4: String a_b;
5: System.out.print($);
6: System.out.print(a_b);
7: } }

C. Compiler error on line 4.: The local variable a_b may not have been initialized.

What is the result of the following code?

String s1 = "Java";
String s2 = "Java";
StringBuilder sb1 = new StringBuilder();
sb1.append("Ja").append("va");
System.out.println(s1 == s2);
System.out.println(s1.equals(s2));
System.out.println(sb1.toString() == s1);
System.out.println(sb1.toString().equals(s1));

C. true is printed out exactly three times: sb1.toString() == s1 is false.

What is the output of the following code? (Choose all that apply)

1:  interface HasTail { int getTailLength(); }
2:  abstract class Puma implements HasTail {
3:    protected int getTailLength() {return 4;}
4:  }
5:  public class Cougar extends Puma {
6:    public static void main(String[] args) {
7:      Puma puma = new Puma();
8:      System.out.println(puma.getTailLength());
9:    }
10:   
11:   public int getTailLength(int length) {return 2;}
12: }

The code will not compile because of line 3: cannot reduce the visibility of the inherited method from HasTail

What is the output of the following program?

1:  public class FeedingSchedule {
2:    public static void main(String[] args) {
3:      boolean keepGoing = true;
4:      int count = 0;
5:      int x = 3;
6:      while(count++ < 3) {
7:        int y = (1 + 2 * count) % 3;
8:        switch(y) {
9:          default:
10:         case 0: x -= 1; break;
11:         case 1: x += 5;
12:       }
13:     }
14:     System.out.println(x);
15:   } }

C. 6: x(3,2,1,6)

What is the output of the following code snippet?

System.out.print("a");
try {
  System.out.print("b");
  throw new IllegalArgumentException();
} catch (RuntimeException e) {
  System.out.print("c");
} finally {
  System.out.print("d");
}
System.out.print("e");

D. abcde

What is the result of the following program?

1: public class MathFunctions {
2: public static void addToInt(int x, int amountToAdd) {
3: x = x + amountToAdd;
4: }
5: public static void main(String[] args) {
6: int a = 15;
7: int b = 10;
8: MathFunctions.addToInt(a, b);
9: System.out.println(a); } }

B. 15: method addToInt does not modify a.

What is the result of the following code?

int[] array = {6,9,8};
List<Integer> list = new ArrayList<>();
list.add(array[0]);
list.add(array[2]);
list.set(1, array[1]);
list.remove(0);
System.out.println(list);

B. [9]: assuming that List and ArrayList are imported

What is the output of the following code?

1:  public class Deer {
2:    public Deer() { System.out.print("Deer"); }
3:    public Deer(int age) { System.out.print("DeerAge"); }
4:    private boolean hasHorns() { return false; }
5:    public static void main(String[] args) {
6:      Deer deer = new Reindeer(5);
7:      System.out.println(","+deer.hasHorns());
8:    }
9:  }
10: class Reindeer extends Deer {
11:   public Reindeer(int age) { System.out.print("Reindeer"); }
12:   public boolean hasHorns() { return true; }
13: }

E. DeerAgeReindeer,false: private method hasHorns with value false cannot be overwritten with public method

Which of the following statements are true? (Choose all that apply)

A. Checked exceptions are intended to be thrown by the JVM (and not the programmer). B. Checked exceptions are required to be caught or declared. C. Errors are intended to be thrown by the JVM (and not the programmer). D. Errors are required to be caught or declared. E. Runtime exceptions are intended to be thrown by the JVM (and not the programmer). F. Runtime exceptions are required to be caught or declared.

A, D, F

Which are true of the following code? (Choose all that apply)

1:  import java.util.*;
2:  public class Grasshopper {
3:    public Grasshopper(String n) {
4:      name = n;
5:    }
6:    public static void main(String[] args) {
7:      Grasshopper one = new Grasshopper("g1");
8:      Grasshopper two = new Grasshopper("g2");
9:      one = two;
10:     two = null;
11:     one = null;
12:   }
13:   private String name; }

D. Immediately after line 10, only one grasshopper object is eligible for garbage collection.

Published

02 August 2015

Category

technical