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J2EE/Java Interview Questions
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JDBC
- What is connection pooling? Why is it used?
- How would you ensure a connection is always freed?
- Write a small piece of pseudo-code to show how you’d open a connection, handle a commit/ rollback, and close the connection.
JSP
- Explain what a JSP is, and talk about the life cycle of a JSP from code to deployment?
- What’s the difference between forwarding on to a different page with HttpRequest.forward(url) and HttpResponse.sendRedirect(url);
- Talk about the differences between different scopes of variables in jsp, e.g. session, page, application scope.
- If there was a problem with login sessions timing out too early, where would you look to see the setting?
XML
- What are the differences between the SAX and the DOM models for parsing. What are their advantages/disadvantages?
- Given this DTD
<!DOCTYPE NEWSPAPER [ <!ELEMENT NEWSPAPER (ARTICLE+)> <!ELEMENT ARTICLE (HEADLINE,BODY)> <!ELEMENT HEADLINE (#PCDATA)> <!ELEMENT BODY (#PCDATA)> <!ATTLIST ARTICLE AUTHOR CDATA #REQUIRED> <!ATTLIST ARTICLE EDITOR CDATA #IMPLIED> ]>
Write out two short bits of XML that would validate based on this DTD.
- Given an exception like this, what would be your thoughts on where to look for the problem?
com.ibm.wcm.xml.sax.SAXParseException: The value of attribute "conditions" must not contain the '<' character. at com.ibm.wcm.apache.xerces.framework.XMLParser.reportError(XMLParser.java:1196) at com.ibm.wcm.apache.xerces.framework.XMLDocumentScanner.reportFatalXMLError(XMLDocumentScanner.java:654) at com.ibm.wcm.apache.xerces.framework.XMLDocumentScanner.scanAttValue(XMLDocumentScanner.java(Compiled Code)) at com.ibm.wcm.apache.xerces.framework.XMLDocumentScanner.scanElement(XMLDocumentScanner.java(Compiled Code)) at com.ibm.wcm.apache.xerces.framework.XMLDocumentScanner$ContentDispatcher.dispatch(XMLDocumentScanner.java(Compiled Code)) at com.ibm.wcm.apache.xerces.framework.XMLDocumentScanner.parseSome(XMLDocumentScanner.java:381) at com.ibm.wcm.apache.xerces.framework.XMLParser.parse(XMLParser.java:1081) at com.ibm.wcm.apache.xerces.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:195) at com.ibm.wcm.common.XMLDocumentProcessor.stringToNode(Unknown Source) at com.ibm.wca.MassLoader.ErrorReporter.ErrorProcessor.createRecordNode(Unknown Source) at com.ibm.wca.MassLoader.ErrorReporter.ErrorProcessor.addError(UnknownSource) at com.ibm.wca.MassLoader.ErrorReporter.DefaultErrorReporter.processErrorEvent(Unknown Source) at com.ibm.wca.MassLoader.ErrorReporter.DefaultErrorReporter.event(Unknown Source) at com.ibm.wca.MassLoader.Events.MassLoaderEventHandler.notifyListners(Unknown Source)(Compiled Code) at com.ibm.wca.MassLoader.Writer.JDBCWriter$WriteWorker.processFailure(Unknown Source) at com.ibm.wca.MassLoader.Writer.JDBCWriter$WriteWorker.run(Unknown Source)(Compiled Code) Error in MassLoading, please check logs for details.
Java
- Explain the ideas behind java.lang.Thread and java.lang.Runnable, and the run() and start() methods.
- Write some pseudo code to show the rough idea of the java.util.Observer / java.util.Observable classes and/or the general Observer/Observable pattern?
- How would you list the contents of a jar file?
- What would this class print out if you ran it?
public class test { public Integer i; public static void main(String[] args) { test t = new test(); System.out.println(" 1: " + t.stringEq() ); String str = "hello 123 there"; trim(str); System.out.println(" 2: " + str ); Integer sq = t.square(t.i); System.out.println(" 3: " + sq ); } public boolean stringEq() { return "abc" == "abc"; } private static void trim(String str) { // remove white space str.replaceAll("\\s", ""); // remove non-letters str.replaceAll("\\W", ""); } private Integer square(Integer i ) { return new Integer(i.intValue() * i.intValue()); } }
EJB
- What are the different types of EJB?
- Draw a diagram showing how EJB usage works, in terms of the different objects which are created and used when you call remote methods on an EJB.