Is Java “pass-by-reference” or “pass-by-value”?

 Java is always pass-by-value.

Unfortunately, we never handle an object at all, instead juggling object-handles called references _{^{(which are passed by value of course)}}. The chosen terminology and semantics easily confuse many beginners.

It goes like this:

public static void main(String[] args) {
    Dog aDog = new Dog("Max");
    Dog oldDog = aDog;

    // we pass the object to foo
    foo(aDog);
    // aDog variable is still pointing to the "Max" dog when foo(...) returns
    aDog.getName().equals("Max"); // true
    aDog.getName().equals("Fifi"); // false
    aDog == oldDog; // true
}

public static void foo(Dog d) {
    d.getName().equals("Max"); // true
    // change d inside of foo() to point to a new Dog instance "Fifi"
    d = new Dog("Fifi");
    d.getName().equals("Fifi"); // true
}

Struts interview questions 10

Q:	What is ActionForm?
A:	An ActionForm is a JavaBean that extends org.apache.struts.action.ActionForm. ActionForm maintains the session state for web application and the ActionForm object is automatically populated on the server side with data entered from a form on the client side.

Q:

What is Struts Validator Framework?

A:

Struts Framework provides the functionality to validate the form data. It can be use to validate the data on the users browser as well as on the server side. Struts Framework emits the java scripts and it can be used validate the form data on the client browser. Server side validation of form can be accomplished by sub classing your From Bean with DynaValidatorForm class. The Validator framework was developed by David Winterfeldt as third-party add-on to Struts. Now the Validator framework is a part of Jakarta Commons project and it can be used with or without Struts. The Validator framework comes integrated with the Struts Framework and can be used without doing any extra settings.

Q:	Give the Details of XML files used in Validator Framework?
A:	The Validator Framework uses two XML configuration files validator-rules.xml and validation.xml. The validator-rules.xml defines the standard validation routines, these are reusable and used in validation.xml. to define the form specific validations. The validation.xml defines the validations applied to a form bean.

Q:	How you will display validation fail errors on jsp page?
A:	Following tag displays all the errors: <html:errors/>

Q:	How you will enable front-end validation based on the xml in validation.xml?
A:	The <html:javascript> tag to allow front-end validation based on the xml in validation.xml. For example the code: <html:javascript formName=\"logonForm\" dynamicJavascript=\"true\" staticJavascript=\"true\" /> generates the client side java script for the form \"logonForm\" as defined in the validation.xml file. The <html:javascript> when added in the jsp file generates the client site validation script.

Q:	How to get data from the velocity page in a action class?
A:	We can get the values in the action classes by using data.getParameter(\"variable name defined in the velocity page\")

Struts interview questions 9

Q:

What is Struts?

A:

The core of the Struts framework is a flexible control layer based on standard technologies like Java Servlets, JavaBeans, ResourceBundles, and XML, as well as various Jakarta Commons packages. Struts encourages application architectures based on the Model 2 approach, a variation of the classic Model-View-Controller (MVC) design paradigm. Struts provides its own Controller component and integrates with other technologies to provide the Model and the View. For the Model, Struts can interact with standard data access technologies, like JDBC and EJB, as well as most any third-party packages, like Hibernate, iBATIS, or Object Relational Bridge. For the View, Struts works well with JavaServer Pages, including JSTL and JSF, as well as Velocity Templates, XSLT, and other presentation systems. The Struts framework provides the invisible underpinnings every professional web application needs to survive. Struts helps you create an extensible development environment for your application, based on published standards and proven design patterns.

Q:	What is Jakarta Struts Framework?
A:	Jakarta Struts is open source implementation of MVC (Model-View-Controller) pattern for the development of web based applications. Jakarta Struts is robust architecture and can be used for the development of application of any size. Struts framework makes it much easier to design scalable, reliable Web applications with Java.

Q:	What is ActionServlet?
A:	The class org.apache.struts.action.ActionServlet is the called the ActionServlet. In the the Jakarta Struts Framework this class plays the role of controller. All the requests to the server goes through the controller. Controller is responsible for handling all the requests.

Q:	How you will make available any Message Resources Definitions file to the Struts Framework Environment?
A:	T Message Resources Definitions file are simple .properties files and these files contains the messages that can be used in the struts project. Message Resources Definitions files can be added to the struts-config.xml file through <message-resources /> tag. Example: <message-resources parameter=\"MessageResources\" />.

Q:

What is Action Class?

A:

The Action Class is part of the Model and is a wrapper around the business logic. The purpose of Action Class is to translate the HttpServletRequest to the business logic. To use the Action, we need to Subclass and overwrite the execute() method. In the Action Class all the database/business processing are done. It is advisable to perform all the database related stuffs in the Action Class. The ActionServlet (commad) passes the parameterized class to Action Form using the execute() method. The return type of the execute method is ActionForward which is used by the Struts Framework to forward the request to the file as per the value of the returned ActionForward object.

Struts interview questions 8

36.What are differences between <bean:message> and <bean:write>

<bean:message>: is used to retrive keyed values from resource bundle. It also supports the ability to include parameters that can be substituted for defined placeholders in the retrieved string.

<bean:message key="prompt.customer.firstname"/>

<bean:write>: is used to retrieve and print the value of the bean property. <bean:write> has no body.

<bean:write name="customer" property="firstName"/>

37.How the exceptions are handled in struts?

Exceptions in Struts are handled in two ways:

• Programmatic exception handling :

Explicit try/catch blocks in any code that can throw exception. It works well when custom value (i.e., of variable) needed when error occurs. 

• Declarative exception handling :You can either define <global-exceptions> handling tags in your struts-config.xml or define the exception handling tags within <action></action> tag. It works well when custom page needed when error occurs. This approach applies only to exceptions thrown by Actions.

<global-exceptions>
 <exception key="some.key"
            type="java.lang.NullPointerException"
            path="/WEB-INF/errors/null.jsp"/>
</global-exceptions>

or

<exception key="some.key"
           type="package.SomeException"
           path="/WEB-INF/somepage.jsp"/>

38.What is difference between ActionForm and DynaActionForm?

• An ActionForm represents an HTML form that the user interacts with over one or more pages. You will provide properties to hold the state of the form with getters and setters to access them. Whereas, using DynaActionForm there is no need of providing properties to hold the state. Instead these properties and their type are declared in the struts-config.xml
• The DynaActionForm bloats up the Struts config file with the xml based definition. This gets annoying as the Struts Config file grow larger.
• The DynaActionForm is not strongly typed as the ActionForm. This means there is no compile time checking for the form fields. Detecting them at runtime is painful and makes you go through redeployment.
• ActionForm can be cleanly organized in packages as against the flat organization in the Struts Config file.
• ActionForm were designed to act as a Firewall between HTTP and the Action classes, i.e. isolate and encapsulate the HTTP request parameters from direct use in Actions. With DynaActionForm, the property access is no different than using request.getParameter( .. ).
• DynaActionForm construction at runtime requires a lot of Java Reflection (Introspection) machinery that can be avoided.

39.How can we make message resources definitions file available to the Struts framework environment?

We can make message resources definitions file (properties file) available to Struts framework environment by adding this file to struts-config.xml.

<message-resources parameter="com.login.struts.ApplicationResources"/>

40.What is the life cycle of ActionForm?

The lifecycle of ActionForm invoked by the RequestProcessor is as follows:

• Retrieve or Create Form Bean associated with Action
• "Store" FormBean in appropriate scope (request or session)
• Reset the properties of the FormBean
• Populate the properties of the FormBean
• Validate the properties of the FormBean

Pass FormBean to Action

Struts interview questions 7

31.What is DynaActionForm?

A specialized subclass of ActionForm that allows the creation of form beans with dynamic sets of properties (configured in configuration file), without requiring the developer to create a Java class for each type of form bean.

32.What are the steps need to use DynaActionForm?

Using a DynaActionForm instead of a custom subclass of ActionForm is relatively straightforward. You need to make changes in two places:

• In struts-config.xml: change your <form-bean> to be an org.apache.struts.action.DynaActionForm instead of some subclass of ActionForm

<form-bean name="loginForm"type="org.apache.struts.action.DynaActionForm" >
    <form-property name="userName" type="java.lang.String"/>
    <form-property name="password" type="java.lang.String" />
</form-bean>

In your Action subclass that uses your form bean:

• import org.apache.struts.action.DynaActionForm
• downcast the ActionForm parameter in execute() to a DynaActionForm
• access the form fields with get(field) rather than getField()

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;


import org.apache.struts.action.DynaActionForm;

public class DynaActionFormExample extends Action {
 public ActionForward execute(ActionMapping mapping, ActionForm form,
   HttpServletRequest request, HttpServletResponse response)
            throws Exception {            
  DynaActionForm loginForm = (DynaActionForm) form;
                ActionMessages errors = new ActionMessages();       
        if (((String) loginForm.get("userName")).equals("")) {
            errors.add("userName", new ActionMessage(
                            "error.userName.required"));
        }
        if (((String) loginForm.get("password")).equals("")) {
            errors.add("password", new ActionMessage(
                            "error.password.required"));
        }
        ...........

33.How to display validation errors on jsp page?

<html:errors/> tag displays all the errors. <html:errors/> iterates over ActionErrors request attribute.

34.What are the various Struts tag libraries?

The various Struts tag libraries are:

• HTML Tags
• Bean Tags
• Logic Tags
• Template Tags
• Nested Tags
• Tiles Tags

35.What is the use of <logic:iterate>?

<logic:iterate> repeats the nested body content of this tag over a specified collection.

<table border=1>
  <logic:iterate id="customer" name="customers">
    <tr>
      <td><bean:write name="customer" property="firstName"/></td>
      <td><bean:write name="customer" property="lastName"/></td>
      <td><bean:write name="customer" property="address"/></td>
   </tr>
  </logic:iterate>
</table>