Saturday, 26 August 2017

Arrays.asList() throws java.lang.UnsupportedOperationException

Arrays.asList() throws java.lang.UnsupportedOperationException

You might get the UnsupportedException when you tries to use the add() method in the List.

If your code looks something similar to this :

String[] data = new String[] {"hari","krushna"};
List<String> asList = Arrays.asList(data);
asList.add("test");

Then you will see the following exception :

java.lang.UnsupportedOperationException
at java.util.AbstractList.add(Unknown Source)
at java.util.AbstractList.add(Unknown Source)
at ArrayConvert.trial(ArrayConvert.java:14)
at ArrayConvert.main(ArrayConvert.java:8)


Solution of the above problem is :
 you need to create an ArrayList or LinkedList and add the objects to the newly created Array/LinkedList:

String[] data = new String[] {"","",""};
List<String> asList = Arrays.asList(data);
List<String> newList = new LinkedList<>(asList);
newList.add("test");

Reason for the UnsupportedOperationException:

Arrays.asList Method is returning a sub class object of Arrays class : java.util.Arrays.ArrayList

Following is the signature of the class :

private static class ArrayList<E> extends AbstractList<E> implements RandomAccessjava.io.Serializable

Here ArrayList extends java.util.AbstractList class.

Following are the add() method in AbstractList:

public boolean add(E e) {
 add(size(), e);
 return true;
}

public void add(int index, E element) {
  throw new UnsupportedOperationException();
}

As you see above add() method is not implemented, so when add() method is called directly from asList() object then it will throw an Exception.

This will be Runtime exception so difficult to identify at the time of coding. 



Thursday, 22 June 2017

Command Parameter RCP (Eclipse RCP)

Command Parameter RCP (Eclipse RCP)

Open MANIFEST.MF file and right click on the Command and select "commandParameter" from "New".

After creating "commandParameter", enter the details, like "id", "name" and make optional as "false".




After adding the parameter in the command, in View (or Editor) at the time of calling the command set the parameter. Refer the following code to set the parameter at the time of execution.

Code in View (or Editor):


ICommandService commandService = (ICommandService) getSite().getService(ICommandService.class);
IHandlerService handlerService = (IHandlerService) getSite().getService(IHandlerService.class);

// Enter the ID of the Command as the argument to getCommand() method in next line.
Command sysoComm = commandService.getCommand("ResumeParser.commands.sampleCommand");

HashMap<String, String> paramsForCommand = new HashMap<String, String>();
// Enter the Command Parameter id as the Key in the following line.
paramsForCommand.put("ResumeParser.commandParameter2"text.getText());

ParameterizedCommand paramCommand = ParameterizedCommand.generateCommand(sysoCommparamsForCommand);

try {
handlerService.executeCommand(paramCommandnull);
catch (Exception ee) {
ee.printStackTrace();
}


Following is the code of execute() method of the Handler (AbstractHandler) class.


/**
* the command has been executed, so extract extract the needed information
* from the application context.
*/
public Object execute(ExecutionEvent event) throws ExecutionException {
        // Provide the id of the "Command Parameter" as the argument of the getParameter method.
String commandValue = event.getParameter("ResumeParser.commandParameter2");
System.out.println(commandValue);
return null;

}

Friday, 16 June 2017

Execute Command from View/Editor in Eclipse RCP

Execute Command from View/Editor in Eclipse RCP

All Commands will be registered to IHandlerService. If we get the IHandlerService instance then we can call the desired command and then execute it.

// Get the Instance of IHandlerService from View
// Alternate way of getting site object is this also:
// PlatformUI.getWorkbench().getActiveWorkbenchWindow().getActivePage().getActivePart().getSite()
// But we prefer  following so we get the appropriate IWorkbenchPartSite object.
IHandlerService service = (IHandlerService) getSite().getService(IHandlerService.class); 
try {
service.executeCommand("ResumeParser.commands.sampleCommand", null); 
} catch (ExecutionException e1) { 
e1.printStackTrace(); 
} catch (NotDefinedException e1) { 
e1.printStackTrace(); 
} catch (NotEnabledException e1) { 
e1.printStackTrace(); 
} catch (NotHandledException e1) { 
e1.printStackTrace(); 
}


Sunday, 11 June 2017

Fie Dialog and Folder Dialog in Eclipse RCP


Fie Dialog and Folder Dialog in Eclipse RCP

File Dialog in Eclipse:
- This will only allow you to select the files in the Dialog Box
FileDialog fileDialog = new FileDialog(PlatformUI.getWorkbench().getActiveWorkbenchWindow().getShell()); // Following line is Optional if you want to, enable filter for specific files. //fileDialog.setFilterExtensions(new String[] {"*.txt","*.csv"}); String filePath = fileDialog.open(); System.out.println(filePath);


Folder Dialog in Eclipse:
- This will allow you to select the folder in the Dialog box.
DirectoryDialog directoryDialog = new DirectoryDialog(PlatformUI.getWorkbench().getActiveWorkbenchWindow().getShell()); // Optional - if you want to open specific path //directoryDialog.setFilterPath("/home/hv185014/junk/"); String directoryPath = directoryDialog.open(); System.out.println(directoryPath);

Thursday, 6 April 2017

Builder Design Pattern - Java

Builder Design Pattern - Java

When the construction of the class contains a large number of argument then this Design Pattern is preferred.

Builder Pattern, as the name suggest, it helps to reduce the complexity in Building Java Object.


public class Person { private String firstname; private String lastname; private String address; private int age; private String city; private String state; public Person(String firstname, String lastname, String address, int age, String city, String state) { super(); this.firstname = firstname; this.lastname = lastname; this.address = address; this.age = age; this.city = city; this.state = state; } }

In the above example, you can see, that the construction of the Person class has 6 arguments and few of them can be optional.

So we can create a new PersonBuilder class which will help to create the Object of the Person class.


public class PersonBuilder { private String firstname; private String lastname; private String address; private int age; private String city; private String state; public PersonBuilder() { } public PersonBuilder setFirstname(String firstname) { this.firstname = firstname; return this; } public PersonBuilder setLastname(String lastname) { this.lastname = lastname; return this; } public PersonBuilder setAddress(String address) { this.address = address; return this; } public PersonBuilder setAge(int age) { this.age = age; return this; } public PersonBuilder setCity(String city) { this.city = city; return this; } public PersonBuilder setState(String state) { this.state = state; return this; } public Person build() { return new Person(firstname, lastname, address, age, city, state); } }

So, now the Person class can be created as below :

If Person is with address and name then it can created as following new PersonBuilder("firstname", "lastname").setAddress("my address").build();

If Person is with state and name then it can created as following new PersonBuilder("firstname", "lastname").setState("guj").build();

Friday, 8 January 2016

Open Eclipse RCP application as maximized

Open Eclipse RCP application as maximized

Open File :

ApplicationWorkbenchWindowAdvisor.java in you RCP application and override the method "postWindowOpen()" and write the code as mentioned below :

@Override
 public void postWindowOpen() {
  super.postWindowOpen();
  IWorkbenchWindowConfigurer configurer = getWindowConfigurer();

  configurer.getWindow().getShell().setMaximized( true );
 }

Following Books are good to refer :


Wednesday, 30 December 2015

Show Perspective switch bar in Eclipse RCP application


Show Perspective switch bar in Eclipse RCP application

Open file ApplicationWorkbenchWindowAdvisor.java in your plug-in project.

Override the method, preWindowOpen and as shown below, setShowPerspectiveBar as True.


 @Override
    public void preWindowOpen ()
    {
        IWorkbenchWindowConfigurer configurer = getWindowConfigurer();
        configurer.setShowPerspectiveBar( true );
    }


Run your RCP application, and on Right side top, you will be able to see perspective Switch.

Following Books are good to refer :