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When you compare the performance of a Java program against that of a C/C++ program, you will find that the current generation of Java programs can be as much as twenty times slower than their C/C++ counterparts. This performance loss is mostly due to the FACT that the browser musf interpret the Java bytecode and convert it into the computer's native code (such as a Pentium or Motorola-specific code) before the code can run. In C/C++, the code is in the processor's native format to begin with, so this time-consuming translation step is not required. Remember, however, that Java's generic bytecode allows the same Java code to run on multiple platforms.
The Java designers are working on various SOLUTIONS to speed up Java. In the MEANTIME, you can use the -O compiler switch with javac, which may increase the applet's performance. The -0 switch directs javac to optimize its bytecode by "inlining" static, final and private methods. For now, don't worry what "inlining" such code means other than it may improve your applet performance. Unfortunately, when you use inlining, you may increase the size of your bytecode FILE, which will increase the applet's download time. The following Javac command illustrates how you use the -0 switch:

When you compare the performance of a Java program against that of a C/C++ program, you will find that the current generation of Java programs can be as much as twenty times slower than their C/C++ counterparts. This performance loss is mostly due to the fact that the browser musf interpret the Java bytecode and convert it into the computer's native code (such as a Pentium or Motorola-specific code) before the code can run. In C/C++, the code is in the processor's native format to begin with, so this time-consuming translation step is not required. Remember, however, that Java's generic bytecode allows the same Java code to run on multiple platforms.
The Java designers are working on various solutions to speed up Java. In the meantime, you can use the -O compiler switch with javac, which may increase the applet's performance. The -0 switch directs javac to optimize its bytecode by "inlining" static, final and private methods. For now, don't worry what "inlining" such code means other than it may improve your applet performance. Unfortunately, when you use inlining, you may increase the size of your bytecode file, which will increase the applet's download time. The following Javac command illustrates how you use the -0 switch:

As you have learned, the javac compiler examines your source-CODE files and produces the bytecode .class files. As your JAVA applets become more complex, it may become difficult for you to locate errors (bugs) within your code. To help you locate such errors, most Java development environments provide a special debugger program. In the CASE of the Sun's Java DEVELOPER's KIT, the debugger program is named jdb (for Java debugger). To provide jdb with more information to work with, the Sun's JDK provides special version of the compiler named javac__g. Sun designed the javac _g compiler for use with debuggers. Essentially, javacjg is a non-optimized version of the javac compiler which place tables of information within the bytecode that the debugger can use to track down errors. To compile a Java applet using the javac__g compiler, you simply specify the applet source-file named within the javac^g command line, as shown here:

As you have learned, the javac compiler examines your source-code files and produces the bytecode .class files. As your Java applets become more complex, it may become difficult for you to locate errors (bugs) within your code. To help you locate such errors, most Java development environments provide a special debugger program. In the case of the Sun's Java Developer's Kit, the debugger program is named jdb (for Java debugger). To provide jdb with more information to work with, the Sun's JDK provides special version of the compiler named javac__g. Sun designed the javac _g compiler for use with debuggers. Essentially, javacjg is a non-optimized version of the javac compiler which place tables of information within the bytecode that the debugger can use to track down errors. To compile a Java applet using the javac__g compiler, you simply specify the applet source-file named within the javac^g command line, as shown here:

• When you create JAVA source-code files that contain classes and methods, you need to be aware of the Java file-naming convention. Each Java source-code file must END with the Java extension. In addition, the file's name must match the name of the public class the file DEFINES. For example, if your source-code file creates a class named MorphaMatic, your source-code file must use the name MorphaMatic.java. As you can see, the LETTERS of the source-code file name must match the class name exactly, INCLUDING the use of upper and lowercase letters.
• The HTML file that you use to run the applet can have any name. As a rule, however, you should use the standard extension for your system, typically .html or .htm. Also, to help organize your files, you may want to use a name similar to that of your applet for the HTML file name, such as MorphaMatic. html.
• Finally, the bytecode file the Java compiler creates will have the .class extension. In this case, the bytecode file will have the name MorphaMatic.class. As discussed, the .class file is the file the Web server downloads to your browser which, in turn, interprets and executes the files's contents.

• Depending on what DEVELOPMENT package you use to create your Java programs, will go about compiling, ORGANIZING, and testing your programs in different ways. However, the general development process is mostly the same no matter which package or platform you use.
• As discussed, the end result of the Java programs development process is a bytecode file which the server downloads to the browser for interpretation and execution. When you compile your Java source file, you are creating a bytecode file. Java source-code files, on the other hand, contain the class definitions and program statements you write using the Java LANGUAGE. In addition to the Java source-code files, you must create a small HTML file, which the browser uses to invoke your applet.
• After the compiler creates the bytecode and you create an HTML file, you can test your applet using either your browser or an appletviewer. If your applet contains errors, many Java development environments provide a debugger program that you can use to track down the errors. When you are ready to RELEASE your applet to the public, you must place the applet and a corresponding HTML file on a Web server.
• Therefore, the general development cycle of a Java applet INCLUDES the creation of source-code and HTML files, compiling the source into bytecode, testing the bytecode through an appletviewer, detecting and removing any errors from the applet using a debugger and, finally, releasing the applet for use on a Web server.

When a Java applet runs over a network, two sides are working. One is the server, which is RESPONSIBLE for maintaining and handling browser requests for the various files it CONTROLS. On the server side, a Java applet is just a FILE like any other file an HTTP server ALREADY handles. You do not need any special server software for Java since the real work of executing the Java applet is performed by the browser, not the server.

On the other side is the client, or browser, which request, receives, and interprets files from the server. The browser is responsible for displaying the Web page, playing sounds, running animations and. in general, determining the type of data the server is sending and handling that data accordingly.

When a Web page contains a Java applet, the page's HTML file will contain an <APPLET> entry. If the browser is Java-enabled, the browser will request the applet file from the server. The server, in turn, will send the applet's bytecode to the browser, which will start its Java INTERPRETER to execute the code.

When a Java applet runs over a network, two sides are working. One is the server, which is responsible for maintaining and handling browser requests for the various files it controls. On the server side, a Java applet is just a file like any other file an HTTP server already handles. You do not need any special server software for Java since the real work of executing the Java applet is performed by the browser, not the server.

On the other side is the client, or browser, which request, receives, and interprets files from the server. The browser is responsible for displaying the Web page, playing sounds, running animations and. in general, determining the type of data the server is sending and handling that data accordingly.

When a Web page contains a Java applet, the page's HTML file will contain an <APPLET> entry. If the browser is Java-enabled, the browser will request the applet file from the server. The server, in turn, will send the applet's bytecode to the browser, which will start its Java interpreter to execute the code.

Most Java development environments include a special program called an appletviewer. using the appletviewer, you can execute your applet just as if it were running within a Web page DISPLAYED a browser. In most cases, the appletviewer can run your applet faster than a browser, making the appletviewer convenient for testing your applet. As you develop your applet, you will want to run it each time you add features. By using the appletviewer, you can quickly TRY out your applet WITHOUT starting your Java-enabled Web browser. You run the appletviewer that accompanies Sun's Java Developer's Kit from the command line, specifying the name of the HTML file that contains the <APPLET> entry for applet you want to VIEW:

Most Java development environments include a special program called an appletviewer. using the appletviewer, you can execute your applet just as if it were running within a Web page displayed a browser. In most cases, the appletviewer can run your applet faster than a browser, making the appletviewer convenient for testing your applet. As you develop your applet, you will want to run it each time you add features. By using the appletviewer, you can quickly try out your applet without starting your Java-enabled Web browser. You run the appletviewer that accompanies Sun's Java Developer's Kit from the command line, specifying the name of the HTML file that contains the <APPLET> entry for applet you want to view:

The Java applets your browser executes reside in a file with the .class extension. When you create a Web page, you can STORE you Java .class files in a directory which is different from the directory that contains the page's HTML files. Within the HTML &LT;APPLET> tag, you can use the CODEBASE attribute to specify the directory within which the applet's .class files reside. The CODEBASE location can be a directory on the same COMPUTER or a directory at ANOTHER computer. The CODEBASE attribute specifies (to the browser) the base URL (relative or specifies) of the directory that contain the .class files. If an <APPLET> tag does not use the CODEBASE attribute, the browser uses the current directory (the one containing the HTML file) to locate the .class files. The following <APPLET> tag directs the browser to look for the applet files in the directory called /server_a/applets.

The Java applets your browser executes reside in a file with the .class extension. When you create a Web page, you can store you Java .class files in a directory which is different from the directory that contains the page's HTML files. Within the HTML <APPLET> tag, you can use the CODEBASE attribute to specify the directory within which the applet's .class files reside. The CODEBASE location can be a directory on the same computer or a directory at another computer. The CODEBASE attribute specifies (to the browser) the base URL (relative or specifies) of the directory that contain the .class files. If an <APPLET> tag does not use the CODEBASE attribute, the browser uses the current directory (the one containing the HTML file) to locate the .class files. The following <APPLET> tag directs the browser to look for the applet files in the directory called /server_a/applets.

You use the <APPLET> tag WIDTH and HEIGHT attributes to SPECIFY the pixel size of an applet WINDOW. In ADDITION to letting you specify the applet window size in TERMS of pixels, many browsers LET you specify the applet window's size as a percentage of the browser's window's size. You do this by specifying a percentage value for the HEIGHT and WIDTH attributes within the <APPLET> tag. For example, the following <APPLET> entry creates an applet window based on 50% of the height and 100% of the width of the browser's window:

You use the <APPLET> tag WIDTH and HEIGHT attributes to specify the pixel size of an applet window. In addition to letting you specify the applet window size in terms of pixels, many browsers let you specify the applet window's size as a percentage of the browser's window's size. You do this by specifying a percentage value for the HEIGHT and WIDTH attributes within the <APPLET> tag. For example, the following <APPLET> entry creates an applet window based on 50% of the height and 100% of the width of the browser's window:

Java applets run within their own WINDOW: Within your HTML file, you set the size of an applet window, using the &LT;APPLET&GT; tag's WIDTH and HEIGHT attributes. The size values you specify for each attribute are in PIXELS. For example, the following <APPLET> entry creates applet window that is 30 pixels tall by 100 pixels wide:

Java applets run within their own window: Within your HTML file, you set the size of an applet window, using the <APPLET> tag's WIDTH and HEIGHT attributes. The size values you specify for each attribute are in pixels. For example, the following <APPLET> entry creates applet window that is 30 pixels tall by 100 pixels wide:

An intranet is an in-house version of the Internet. An intranet uses the same technologies, software, and equipment that the Internet uses (PRIMARILY TCP/IP). Whereas the Internet has information servers MILES away controlled by other organizations, your company controls the servers and client computers inside your office in an intranet. During the past YEAR, intranets have experienced explosive popularity growth because they offer a very low cost way for companies to maintain and distribute internal information in an easy-to-use format.
Because intranets work like the Internet, Java also finds a home on company intranets. All the techniques that you will learn and, in fact the same applets that you will use for the Internet, may be applied in your intranet. You may find that Java applets will help you solve special software problems within the intranet. You can use applets to provide a friendly interface to company databases, documentation STORES, equipment controls, and so on, while running on any computer from a Mac to a PC to a UNIX workstation.

An intranet is an in-house version of the Internet. An intranet uses the same technologies, software, and equipment that the Internet uses (primarily TCP/IP). Whereas the Internet has information servers miles away controlled by other organizations, your company controls the servers and client computers inside your office in an intranet. During the past year, intranets have experienced explosive popularity growth because they offer a very low cost way for companies to maintain and distribute internal information in an easy-to-use format.
Because intranets work like the Internet, Java also finds a home on company intranets. All the techniques that you will learn and, in fact the same applets that you will use for the Internet, may be applied in your intranet. You may find that Java applets will help you solve special software problems within the intranet. You can use applets to provide a friendly interface to company databases, documentation stores, equipment controls, and so on, while running on any computer from a Mac to a PC to a UNIX workstation.

Sun designed Java from the start to fit hand-in-glove on the Internet. Applets are special Java PROGRAMS that execute from within a Web browser. In contrast, a Java application (an application PROGRAM as opposed to an applet) does not run within a browser. As it turns out, Java applets are not much different from standalone Java application. You can start developing your Java program from either an applet or an application and cross over any time. For example, assume that you are writing a new Java-based application that is initially designed as a standalone (non-Internet) GAME for Mac COMPUTERS. At the end of your program's development CYCLE, you decide that you want it to run on Web browsers. Your task to make it into a Web-based applet involves very trivial changes, and the addition of some simple HTML code. At the same time, you will find that the game will also run on computers other than Macs! The point you should remember is that Java applets run within browsers across the Web, whereas Java application programs do not.

Sun designed Java from the start to fit hand-in-glove on the Internet. Applets are special Java programs that execute from within a Web browser. In contrast, a Java application (an application program as opposed to an applet) does not run within a browser. As it turns out, Java applets are not much different from standalone Java application. You can start developing your Java program from either an applet or an application and cross over any time. For example, assume that you are writing a new Java-based application that is initially designed as a standalone (non-Internet) game for Mac computers. At the end of your program's development cycle, you decide that you want it to run on Web browsers. Your task to make it into a Web-based applet involves very trivial changes, and the addition of some simple HTML code. At the same time, you will find that the game will also run on computers other than Macs! The point you should remember is that Java applets run within browsers across the Web, whereas Java application programs do not.

If you are already familiar with C/C++, you will find that Java is actually a SIMPLER language to master. Java incorporates the basic tenets of object-oriented design, yet it eliminates some of the more COMPLICATED of the other language, such as multiple inheritance and templates. Many of the language keywords are the same or have only minor differences, which increases portability.
If you are a C programmer dreading the seemingly inevitable push toward C++, you may rejoice over Java's CLEANER approach to object-oriented programming. In fact, you want to skip C++ altogether and learn Java instead. Java's MANAGEABLE selection of predefined CLASSES are both useful and easy to understand. Many of the common operations that may take you hundreds or thousands of lines of code are already done for you. For example, you can write a simple network chat program without having to know much about sockets, protocols, and other low-level network issues.

If you are already familiar with C/C++, you will find that Java is actually a simpler language to master. Java incorporates the basic tenets of object-oriented design, yet it eliminates some of the more complicated of the other language, such as multiple inheritance and templates. Many of the language keywords are the same or have only minor differences, which increases portability.
If you are a C programmer dreading the seemingly inevitable push toward C++, you may rejoice over Java's cleaner approach to object-oriented programming. In fact, you want to skip C++ altogether and learn Java instead. Java's manageable selection of predefined classes are both useful and easy to understand. Many of the common operations that may take you hundreds or thousands of lines of code are already done for you. For example, you can write a simple network chat program without having to know much about sockets, protocols, and other low-level network issues.

When PEOPLE talk about code being robust, they are referring to the code's reliability. Although Java has not eliminated unreliable code, it has made writing high-quality software easier. To begin, Java eliminates many of the memory problems that are common in languages such as C and C++. Java does not support direct access to pointers to memory. As a result, a Java applet cannot corrupt your computer's memory. Also, Java performs run-time CHECKS (while the applet is RUNNING) to make sure that all array and string references are within each items's bounds. In other programming languages, many software bugs result from the PROGRAM not freeing memory that ought to be freed or freeing the same memory more than once. Java, on the other hand, performs automatic garbage collection (which releases unused memory), eliminating the program's need to free unused memory.
Next, Java is more strongly typed than C++ and requires method declarations, which reduces the potential for type-mismatch errors. Finally, Java institutes an error trapping method known as exception handling. When a program error occurs Java signals the program with an exception, which provides the program with a chance to recover from the error- and warns the user that something caused a specific operation to fail.

When people talk about code being robust, they are referring to the code's reliability. Although Java has not eliminated unreliable code, it has made writing high-quality software easier. To begin, Java eliminates many of the memory problems that are common in languages such as C and C++. Java does not support direct access to pointers to memory. As a result, a Java applet cannot corrupt your computer's memory. Also, Java performs run-time checks (while the applet is running) to make sure that all array and string references are within each items's bounds. In other programming languages, many software bugs result from the program not freeing memory that ought to be freed or freeing the same memory more than once. Java, on the other hand, performs automatic garbage collection (which releases unused memory), eliminating the program's need to free unused memory.
Next, Java is more strongly typed than C++ and requires method declarations, which reduces the potential for type-mismatch errors. Finally, Java institutes an error trapping method known as exception handling. When a program error occurs Java signals the program with an exception, which provides the program with a chance to recover from the error- and warns the user that something caused a specific operation to fail.

A computer virus is a program written by someone who to maliciously damage the FILES you have stored on your disks or your computer's disk itself. To encounter a virus from across the Internet, you MUST download and run a program. Unfortunately, with Java applets, a remote sever downloads the applet to a browser on your system which, in turn, runs the applet. At first glance these downloaded Java applets are an ideal way for MALICIOUS programmers to create viruses. Luckily, the Java developers designed Java with networking in mind. Therefore, Java has several built-in security defenses which reduce a programmer's ability to use Java to create a virus.
First, Java applets cannot read or write local files that reside on your disk. In this way, the applet cannot store the virus on your disk or attach the virus to a file. That the applet simply cannot perform disk INPUT and output. Second, Java applets are "blind" to your computer's memory layout. Specifically, Java applets do not have pointers to memory, and programmers cannot use this traditional back door to your computer. Third, Java cannot use memory outside its own memory space. By building these precautions into programming language itself, the Java developers have GREATLY impaired Java's use in creating and transmitting computer viruses.

A computer virus is a program written by someone who to maliciously damage the files you have stored on your disks or your computer's disk itself. To encounter a virus from across the Internet, you must download and run a program. Unfortunately, with Java applets, a remote sever downloads the applet to a browser on your system which, in turn, runs the applet. At first glance these downloaded Java applets are an ideal way for malicious programmers to create viruses. Luckily, the Java developers designed Java with networking in mind. Therefore, Java has several built-in security defenses which reduce a programmer's ability to use Java to create a virus.
First, Java applets cannot read or write local files that reside on your disk. In this way, the applet cannot store the virus on your disk or attach the virus to a file. That the applet simply cannot perform disk input and output. Second, Java applets are "blind" to your computer's memory layout. Specifically, Java applets do not have pointers to memory, and programmers cannot use this traditional back door to your computer. Third, Java cannot use memory outside its own memory space. By building these precautions into programming language itself, the Java developers have greatly impaired Java's use in creating and transmitting computer viruses.

When you write and COMPILE a Java applet, you end up with a platform-independent FILE called a bytecode. Like a standard program, a bytecode consists of ones and zeros. Unlike a standard program, however, the bytecode is not processor specific. In other words, the bytecode does not correspond to an Intel Pentium or a Motorola processor. Instead, after the server DOWNLOADS the bytecode to your browser, special code within the browser reads and interprets the bytecode, in turn running the applet. To run the bytecode in this way, the interpreter translates the platform independent ones and zeros into ones and zeros your computer's processor understands. In other words, it maps the bytecode to ones and zeros that correspond to the current processor, such as a Pentium.
Each computer platform (Mac, Windows, and so on) can have its own Java interpreter. However, the bytecode file that the server downloads to each browser is identical. In this way, you use the same bytecode on a browser running on a Mac, a PC, or a Silicon Graphics workstation. The multi-platform bytecode file is just one aspect of Java's portability. Java's designers also took the EXTRA EFFORT to remove any platform dependence in the Java language. Thus, you will not find any hardware specific references in Java.

When you write and compile a Java applet, you end up with a platform-independent file called a bytecode. Like a standard program, a bytecode consists of ones and zeros. Unlike a standard program, however, the bytecode is not processor specific. In other words, the bytecode does not correspond to an Intel Pentium or a Motorola processor. Instead, after the server downloads the bytecode to your browser, special code within the browser reads and interprets the bytecode, in turn running the applet. To run the bytecode in this way, the interpreter translates the platform independent ones and zeros into ones and zeros your computer's processor understands. In other words, it maps the bytecode to ones and zeros that correspond to the current processor, such as a Pentium.
Each computer platform (Mac, Windows, and so on) can have its own Java interpreter. However, the bytecode file that the server downloads to each browser is identical. In this way, you use the same bytecode on a browser running on a Mac, a PC, or a Silicon Graphics workstation. The multi-platform bytecode file is just one aspect of Java's portability. Java's designers also took the extra effort to remove any platform dependence in the Java language. Thus, you will not find any hardware specific references in Java.

Java is an object-oriented programming language which means you can use Java to develop your programs in terms of data and the methods (functions) that operate on the data. In Java, a class is a COLLECTION of the data and methods which describe an object with which your program works. Think of an object as a "THING," such as a graphics IMAGE, a dialog box, or a file.
Java APPLETS can ARRANGE classes in hierarchical fashion which means you can build new classes from existing classes, improving upon or extending the existing class's capabilities. Everything in Java, except for a few primitive types such as numbers, characters, and boolean (true and false) types, is an object. Java comes with an extensive set of classes that you can use in your programs. In fact, a Java applet itself is a Java class.

Java is an object-oriented programming language which means you can use Java to develop your programs in terms of data and the methods (functions) that operate on the data. In Java, a class is a collection of the data and methods which describe an object with which your program works. Think of an object as a "thing," such as a graphics image, a dialog box, or a file.
Java applets can arrange classes in hierarchical fashion which means you can build new classes from existing classes, improving upon or extending the existing class's capabilities. Everything in Java, except for a few primitive types such as numbers, characters, and boolean (true and false) types, is an object. Java comes with an extensive set of classes that you can use in your programs. In fact, a Java applet itself is a Java class.

Programmers often mention the name "HotJava" in the same BREATH as Java. Whereas Java is a programming language, HotJava was the first Web browser that could download and play (execute) Java applets. HotJava, created by SUN, is simply a browser, much like the Netscape Navigator or Microsoft's INTERNET Explorer.
Although HotJava was the first browser to support Java applets, many browsers now support or will soon support applets. Starting with Netscape Navigator 2.0, for example, you can play Java applets for many PLATFORMS (Windows 95, the Mac, and so on). Another distinguishing feature of HotJava is that unlike most browsers which are WRITTEN in C/C++, the HotJava browser is written with the Java programming language.

Programmers often mention the name "HotJava" in the same breath as Java. Whereas Java is a programming language, HotJava was the first Web browser that could download and play (execute) Java applets. HotJava, created by Sun, is simply a browser, much like the Netscape Navigator or Microsoft's Internet Explorer.
Although HotJava was the first browser to support Java applets, many browsers now support or will soon support applets. Starting with Netscape Navigator 2.0, for example, you can play Java applets for many platforms (Windows 95, the Mac, and so on). Another distinguishing feature of HotJava is that unlike most browsers which are written in C/C++, the HotJava browser is written with the Java programming language.

Java is an object-programming language that was designed to be portable across multiple platforms and operating systems. Developed by SUN Microsystems, Java is modeled after the C++ programming language and includes special features that make it ideal for PROGRAMS on the Internet. STILL, you may be wondering why Java is suddenly receiving so much hype, and what possible improvements could have been made to this new language so as to push aside a well-established language such as C++.
First and foremost, Java makes it easy to put interactive graphics and other special effects on a World WIDE Web page. As with any programming language, Java lets you write programs. Special Java programs, called applets, execute inside a Web page with a capacity matching that of any traditional PROGRAM. Furthermore, when you run a Java applet, the remote server, Java transmits the applet to your browser across the Internet. So rather than going out to a computer store to buy software, Java applets let you download applications automatically when you need them.

Java is an object-programming language that was designed to be portable across multiple platforms and operating systems. Developed by Sun Microsystems, Java is modeled after the C++ programming language and includes special features that make it ideal for programs on the Internet. Still, you may be wondering why Java is suddenly receiving so much hype, and what possible improvements could have been made to this new language so as to push aside a well-established language such as C++.
First and foremost, Java makes it easy to put interactive graphics and other special effects on a World Wide Web page. As with any programming language, Java lets you write programs. Special Java programs, called applets, execute inside a Web page with a capacity matching that of any traditional program. Furthermore, when you run a Java applet, the remote server, Java transmits the applet to your browser across the Internet. So rather than going out to a computer store to buy software, Java applets let you download applications automatically when you need them.

No. To achieve this you have to DEPLOY your EJB MULTIPLE times each SPECIFYING a DIFFERENT JNDI name.

No. To achieve this you have to deploy your EJB multiple times each specifying a different JNDI name.

No. A CLASS is not a SUBCLASS of itself.

No. A class is not a subclass of itself.

Hellonull.

Hellonull.

Java is compiled to be a byte code which is the intermediate language between SOURCE code and machine code. This byte code is not PLATORM SPECIFIC and hence can be fed to any platform. After being fed to the JVM, which is specific to a particular operating system, the code platform specific machine code is generated THUS making java platform INDEPENDENT.

Java is compiled to be a byte code which is the intermediate language between source code and machine code. This byte code is not platorm specific and hence can be fed to any platform. After being fed to the JVM, which is specific to a particular operating system, the code platform specific machine code is generated thus making java platform independent.

ABSTRACTION, ENCAPSULATION, POLYMORPHISM and INHERITANCE.

Abstraction, Encapsulation, Polymorphism and Inheritance.

A class is a definition or prototype WHEREAS an object is an INSTANCE or LIVING representation of the prototype.

A class is a definition or prototype whereas an object is an instance or living representation of the prototype.

Without getting into LENGTHY debates, it is generally accepted that protocols like HTTP are STATELESS i.e. there is no retention of STATE between a TRANSACTION which is a single REQUEST response combination.

Without getting into lengthy debates, it is generally accepted that protocols like HTTP are stateless i.e. there is no retention of state between a transaction which is a single request response combination.

All Java method arguments are passed by VALUE. HOWEVER, Java does manipulate objects by REFERENCE, and all OBJECT VARIABLES themselves are references.

All Java method arguments are passed by value. However, Java does manipulate objects by reference, and all object variables themselves are references.

YES they can. RMI is AVAILABLE with IIOP as the transport PROTOCOL instead of JRMP.

Yes they can. RMI is available with IIOP as the transport protocol instead of JRMP.

The MAIN reason you cannot create a button by Button BT= "abc"; is because "abc" is a literal string (something slightly DIFFERENT than a String object, by-the-way) and bt is a Button object. The only object in JAVA that can be ASSIGNED a literal String is java.lang.String. Important to note that you are NOT calling a java.lang.String constuctor when you type String s = "abc";

The main reason you cannot create a button by Button bt= "abc"; is because "abc" is a literal string (something slightly different than a String object, by-the-way) and bt is a Button object. The only object in Java that can be assigned a literal String is java.lang.String. Important to note that you are NOT calling a java.lang.String constuctor when you type String s = "abc";

Abstract keyword DECLARES either a method or a class. If a method has a abstract keyword in FRONT of it,it is called abstract method.Abstract method has no body.It has only arguments and return type.Abstract methods act as placeholder methods that are implemented in the subclasses.

Abstract classes can’t be instantiated.If a class is declared as abstract,no objects of that class can be created.If a class CONTAINS any abstract method it must be declared as abstract.

Abstract keyword declares either a method or a class. If a method has a abstract keyword in front of it,it is called abstract method.Abstract method has no body.It has only arguments and return type.Abstract methods act as placeholder methods that are implemented in the subclasses.

Abstract classes can’t be instantiated.If a class is declared as abstract,no objects of that class can be created.If a class contains any abstract method it must be declared as abstract.

The Serializable INTERFACE is just a "marker" interface, with no METHODS of its own to implement. Other ’marker’ INTERFACES are
java.rmi.Remote
java.util.EventListener

The Serializable interface is just a "marker" interface, with no methods of its own to implement. Other ’marker’ interfaces are
java.rmi.Remote
java.util.EventListener

It makes no difference in the generated class files since only the CLASSES that are actually used are referenced by the generated class FILE. There is another practical BENEFIT to importing single classes, and this arises when two (or more) packages have classes with the same name. Take java.util.Timer and javax.swing.Timer, for example. If I import java.util.* and javax.swing.* and then try to use "Timer", I get an error while compiling (the class name is ambiguous between both packages). Let’s say what you really wanted was the javax.swing.Timer class, and the only classes you plan on using in java.util are Collection and HashMap. In this case, some people will prefer to import java.util.Collection and import java.util.HashMap instead of importing java.util.*. This will now ALLOW them to use Timer, Collection, HashMap, and other javax.swing classes without using fully qualified class NAMES in.

It makes no difference in the generated class files since only the classes that are actually used are referenced by the generated class file. There is another practical benefit to importing single classes, and this arises when two (or more) packages have classes with the same name. Take java.util.Timer and javax.swing.Timer, for example. If I import java.util.* and javax.swing.* and then try to use "Timer", I get an error while compiling (the class name is ambiguous between both packages). Let’s say what you really wanted was the javax.swing.Timer class, and the only classes you plan on using in java.util are Collection and HashMap. In this case, some people will prefer to import java.util.Collection and import java.util.HashMap instead of importing java.util.*. This will now allow them to use Timer, Collection, HashMap, and other javax.swing classes without using fully qualified class names in.

Logical Data Independence - MEANING IMMUNITY of EXTERNAL SCHEMAS to changed in conceptual SCHEMA.

Physical Data Independence - meaning immunity of conceptual schema to changes in the internal schema.

Logical Data Independence - meaning immunity of external schemas to changed in conceptual schema.

Physical Data Independence - meaning immunity of conceptual schema to changes in the internal schema.

APART from the exceptions already defined in Java package libraries, user can define his own exception CLASSES by extending Exception class.

Apart from the exceptions already defined in Java package libraries, user can define his own exception classes by extending Exception class.

Yes.

Yes.

Yes.

Yes.

Reclaiming the unused MEMORY by the INVALID OBJECTS. Garbage COLLECTOR is responsible for this process.

Reclaiming the unused memory by the invalid objects. Garbage collector is responsible for this process.

No.

No.

Yes.

Yes.

Select part is useful in selecting text or part of the text. Arguments specified for the select command are the same as applicable to substring. First index is usually represents the START of the index. END of line makers are counted as ONE CHARACTER. EXAMPLE t.select (10,15) .

Select part is useful in selecting text or part of the text. Arguments specified for the select command are the same as applicable to substring. First index is usually represents the start of the index. End of line makers are counted as one character. Example t.select (10,15) .

There are two TYPES of exceptions in java. CHECKED exceptions and Unchecked exceptions. Any exception that is is derived from Throwable and Exception is called checked exception except RuntimeException and its sub classes. The COMPILER will check whether the exception is caught or not at COMPILE time. We need to catch the checked exception or declare in the throws clause. Any exception that is derived from Error and RUNTIME Exception is called unchecked exception. We don't need to explicitly catch a unchecked exception.

There are two types of exceptions in java. Checked exceptions and Unchecked exceptions. Any exception that is is derived from Throwable and Exception is called checked exception except RuntimeException and its sub classes. The compiler will check whether the exception is caught or not at compile time. We need to catch the checked exception or declare in the throws clause. Any exception that is derived from Error and Runtime Exception is called unchecked exception. We don't need to explicitly catch a unchecked exception.

notify wakes up a single thread that is waiting for object's monitor. If any threads are waiting on this object, one of them is CHOSEN to be AWAKENED. The choice is ARBITRARY and occurs at the discretion of the implementation. NOTIFYALL Wakes up all threads that are waiting on this object's monitor. A thread waits on an object's monitor by CALLING one of the wait methods.

notify wakes up a single thread that is waiting for object's monitor. If any threads are waiting on this object, one of them is chosen to be awakened. The choice is arbitrary and occurs at the discretion of the implementation. notifyAll Wakes up all threads that are waiting on this object's monitor. A thread waits on an object's monitor by calling one of the wait methods.

A static variable is ASSOCIATED with the CLASS as a whole rather than with SPECIFIC instances of a class. There will be only one value for static variable for all instances of that class. Non-static VARIABLES take on unique values with each object instance.

A static variable is associated with the class as a whole rather than with specific instances of a class. There will be only one value for static variable for all instances of that class. Non-static variables take on unique values with each object instance.

There are three ways for a thread to enter into waiting STATE. By invoking its SLEEP() method, by blocking on I/O, by unsuccessfully ATTEMPTING to acquire an OBJECT's LOCK, or by invoking an object's wait() method.

There are three ways for a thread to enter into waiting state. By invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method.

If statement is used to select from two alternatives. It uses a boolean expression to DECIDE which alternative should be executed. The expression in if must be a boolean VALUE. The SWITCH statement is used to select from multiple alternatives. The case values must be promoted to an to INT value.

If statement is used to select from two alternatives. It uses a boolean expression to decide which alternative should be executed. The expression in if must be a boolean value. The switch statement is used to select from multiple alternatives. The case values must be promoted to an to int value.

Access modifier specify where a METHOD or ATTRIBUTE can be USED.

• Public is accessible from anywhere.
• Protected is accessible from the same class and its SUBCLASSES.
• Package/Default are accessible from the same package.
• Private is only accessible from within the class.

Access modifier specify where a method or attribute can be used.

When assigning an object to a VARIABLE, we are ACTUALLY assigning the memory address of that object to the variable. So the value passed is actually the memory LOCATION of the object. This RESULTS in object aliasing, meaning you can have many variables referring to the same object on the heap.

When assigning an object to a variable, we are actually assigning the memory address of that object to the variable. So the value passed is actually the memory location of the object. This results in object aliasing, meaning you can have many variables referring to the same object on the heap.

An advantage of this SCHEME is that it can run in small chunks of time CLOSELY linked with the execution of the PROGRAM. These characteristic makes it particularly suitable for real-time environments where the program can't be interrupted for very long time. A DISADVANTAGE of reference counting is that it does not detect cycles. A cycle is two or more objects that REFER to one another. Another disadvantage is the overhead of incrementing and decrementing the reference count each time. Because of these disadvantages, reference counting currently is out of favor.

An advantage of this scheme is that it can run in small chunks of time closely linked with the execution of the program. These characteristic makes it particularly suitable for real-time environments where the program can't be interrupted for very long time. A disadvantage of reference counting is that it does not detect cycles. A cycle is two or more objects that refer to one another. Another disadvantage is the overhead of incrementing and decrementing the reference count each time. Because of these disadvantages, reference counting currently is out of favor.

The ThreadPool class is a GENERIC implementation of a thread pool, which takes the following input SIZE of the pool to be constructed and name of the class which implements RUNNABLE (which has a visible default constructor) and constructs a thread pool with active threads that are waiting for activation. once the threads have FINISHED processing they come back and wait once again in the pool.

The ThreadPool class is a generic implementation of a thread pool, which takes the following input Size of the pool to be constructed and name of the class which implements Runnable (which has a visible default constructor) and constructs a thread pool with active threads that are waiting for activation. once the threads have finished processing they come back and wait once again in the pool.

While DEFINING method, VARIABLES passed in the method are CALLED parameters. While using those methods, VALUES passed to those variables are called ARGUMENTS.

While defining method, variables passed in the method are called parameters. While using those methods, values passed to those variables are called arguments.

An argument can be passed in TWO ways.

Passing by value: This method copies the value of an argument into the FORMAL parameter of the SUBROUTINE.

Passing by REFERENCE: In this method, a reference to an argument (not the value of the argument) is passed to the parameter.

An argument can be passed in two ways.

Passing by value: This method copies the value of an argument into the formal parameter of the subroutine.

Passing by reference: In this method, a reference to an argument (not the value of the argument) is passed to the parameter.