A NullPointerException is a runtime exception that indicates the Java Virtual Machine attempted to call a method on an object, but the object reference was null. This case may occur when a reference is assigned from another method call that may return a null value, such as a Hashtable look-up.

The hashCode() method is used in hash-based data stores to get a "nearly unique" identifier for each object. The hash code is used to speed up the search process, so should have a high probability of being different from any other instance. It is possible for two hash codes to be the same, so the equals method is used to make an exact match.

Normally when we compare two objects we use the fundamental equals(Object) method. Conceptually, the equals method "belongs" to the objects you are comparing and returns a boolean to indicate whether they are passed a reference to themselves. Its not obvious why you would choose to make that comparison in the constructor of another class, which may only return a reference to the new instance, not a simple boolean response.

When submitting a job to the indexer through the java API, you must add specifyIdxJobInfoArguments.jobProp.startArray or a NullPointerException error is returned. For example:

This is a somewhat arbitrary distinction to make about Java development, since applications often have front- and back-end components and it is important to understand how both aspects are integrated. In general terms, back-end development is concerned with database storage and retrieval, servlets, Web application frameworks and Enterprise Java Beans.

The major release versions of the Sun Java Software Development Kit (SDK, also known as the JDK) include significant API changes that provide extra programming features built upon the core Java software platform. That means that the basic features of the Java language do not change from one release to the next, so most existing programs will run successfully when compiled with the new SDK.

One of the key benefits of inheritance is to minimise the amount of duplicate code in an application by sharing common code amongst several subclasses. Where equivalent code exists in two related classes, the hierarchy can usually be refactored to move the common code up to a mutual superclass. This also tends to result in a better organisation of code and smaller, simpler compilation units. There are two forms of inheritance in the Java language.

The DriverManager class is a core part of the java.sql package for Java database connectivity, it provides a registry of JDBC drivers that are loaded and available for use, and methods to get database connections using those drivers. The JDBC specification requires implementations of the java.sql.Driver interface to register themselves with the DriverManager method registerDriver(Driver) when their class is loaded through the Class.forName(String) method.

There is no direct management of the storage size of code that is held in memory by the Java Virtual Machine (JVM). The virtual machine manages the allocation and de-allocation of storage through an integral garbage collection system. The JVM keeps track of all object references and periodically disposes of de-referenced objects to free memory.

The Java compiler is a program like any other and your operating system needs to know where to find the executable file. The simplest way to do this is to give the full path to the Java compiler in the command, as below for Windows...

There are two main divisions of data types in Java: object and primitive types. Object types are declared according to their class. Object object = new Object(); Objects can also be cast to a more general superclass or interface type. This is known as polymorphism, which means the object behaves like, and can be treated as, an instance of the more general type. // Type cast Object object = new StringBuffer("Example"); // Interface Comparable object = new File("c:\Example.

Perhaps because InterProlog assumes that its own Prolog files are in a jar file, and is unable to read them. You need to use an extra javaMessage to obtain a full object specification; say your InvisibleObject is X and you want a specification for the referred object in S : ipPrologEngine(E), javaMessage(E,S,getRealJavaObject(X))

According to posts in webtv.users from Steve Perlman, ex-president of WebTV, WebTV has been working to provide a form of Personal Java for the WebTV Plus terminal (and possibly the new Classics and Dishplayer, but nothing was said specifically about them as they were not announced products at the time of the posts)?there is no guarantee this will happen. For the full text of Steve's posts, click here.

For simple mathematical functions a method would usually declare the input variables as method arguments and a return type that matches the required numeric type for the result. In the simplest case an add(int, int) method would return an int value, as below: public final int add(final int firstInt, final int secondInt) { return firstInt + secondInt; } To round a double value up and convert it to an int value takes two operations. The static Math.

Thinking In Java by Bruce Eckel is a good beginner's book on Java, which is available as a free download too.

The JDK, also called the Java Software Development Kit (SDK), is the full suite of tools required to develop, package and publish Java applications. The Sun Java SDK includes the full Java class library, with a compiler, decompiler, profiler, JAR signer, key signing tool and many other tools.

Java is an object oriented language, but there is no standard that defines a "fully" object oriented language, it is a matter of definition and opinion.

Yes. The SQLJ runtime environment consists of a thin layer of pure Java code together with the JDBC driver being used. Oracle offers the 100% Java JDBC Thin driver, which is roughly 150K compressed and can be downloaded into a client browser along with the applet. In your applet code, specify the Oracle JDBC Thin driver for your database connections. See the SQLJ Developer's Guide and Reference for more information. JDK 1.1.x or higher is still required.

Java applets can be downloaded through the proxy. These applets can then create any necessary network connections.

Currently most of the applets at The Applet Depot are compiled under Java1.0.2. They should work with all Java compliant browsers which are available today. Applets written in other versions of Java will be appropriately noted (for example, '1.1j' denotes applets written in Java version 1.1+). Java 1.1+ is not supported by older browsers; Netscape did not fully support it until version 4.06 and higher (earlier versions of 4.0 required a patch). Internet Explorer seems to support Java 1.

A Saffola Oil is an all purpose cooking oil. Its light, clear color and mild, delicate flavor make it excellent for salads, sauteing, and baking. And because Saffola Oil is high in monounsaturates, it is extremely heat stable, excellent for frying, and can be used in place of any cooking oil.

I have just completed CSS: An Interactive Tutorial for Beginners, which covers virtually every aspect of cascading style sheets recommendation 1. I am working on a JavaScript Guide. Yes. Any HTML tag that your browser supports will work in the box. So you can carry tags from chapters to chapters and mix and match... use your imagination! Be creative!

The implicit page variable is simply a "this" reference to the JSP instance that is being invoked by the servlet container. This is an object provided by the container that fulfils the JspPage interface, and normally the HttpJspPage interface too. These interfaces are similar to the Servlet and HttpServlet interfaces and implement JSP lifecycle methods jspInit, jspDestroy and _jspService(HttpServletRequest, HttpServletResponse).

Yes, it can be programmatically accessed by virtually any development environment that conforms to the required standards. The MapPoint Web Service API is a standard SOAP XML-based Web service exposed through WSDL. So long as your development platform of choice supports SOAP web service standards, it can be used with MapPoint Web Service, Because the Map Control is a client side component run in the web browser, there is no dependency on the development environment.

HotJava Views 1.1 is using JNDI to access LDAP. Enterprise APIs such as Enterprise JavaBeans, Java Message Service, JDBC 2.0 make use of JNDI to for their naming and directory needs. RMI over IIOP applications can use JNDI to access the CORBA (COS) naming service.

There are two ways to control this. If you get an OutOfMemoryError when Cocoon is generating pages, see the first paragraph. If you get an OutOfMemoryError when outside of Cocoon (e.g., copying raw files), see the second paragraph. The maxmemory property in the forrest.properties file controls how much memory Cocoon uses. Like many other properties you can copy them from the default configuration at src/core/fresh-site/forrest.

See the following code public class MyClass{ public static void main(String[] s) { MyClass m = new MyClass(); System.out.println(MyClass.class); // class MyClass System.out.println(m.getClass()); // class MyClass } } I did a search in JDK source code. No class as a field anywhere, not in Class class, not in Object class, absolutely nowhere. It is the keyword class can be used this way, to return the Class instance object of MyClass.See details in JLS.