Question 1

Question 1Write a short note on types of Java programs.

Accepted Answer

There are two types of Java programs — Java Stand-Alone Applications and Java Applets.Java Stand-Alone ApplicationsA stand-alone Java application refers to a Java program that can run independently on a computer. Acrobat Reader is an excellent example of this type of application. In Java, every stand-alone application begins its execution with the main() method. Java stand-alone applications can be classified into two types:a. Console based applicationsb. Graphical User Interface based applicationsJava AppletsJava applets are Java applications that run within a web browser. They are mainly used for internet programming. The applet is capable of performing many tasks on a web page, such as displaying graphics, playing sounds, and accepting user input.

Question 2

Question 2How is Java platform independent?

Accepted Answer

Java applications are platform independent, which means that Java applications can be run on any platform. After Java source code is compiled, it is converted into bytecode. The bytecode is then interpreted by the JVM. JVM can be installed on several different operating systems such as Windows, UNIX, Macintosh, etc. JVM allows Java programs to run on almost any computer regardless of its hardware configuration. Due to this factor, Java is considered as a platform independent language.

Question 3

Question 3Describe the traditional compilation process with a suitable diagram.

Accepted Answer

In traditional compilation process, the machine language code generated by the compiler is specific to the platform for which the source code is compiled. Every high-level language has a separate platform specific compiler to generate the machine code that can run on the specific platform. For example, the executable file generated by compiling a C++ program on Windows platform will not run on Macintosh. It needs to be compiled with C++ Macintosh compiler. The below diagram illustrates this:

Question 4

Question 4Describe the Java compilation process with a suitable diagram.

Accepted Answer

In Java compilation process, the source code of a Java program is compiled to an intermediate binary code called the Bytecode. This Bytecode cannot be directly executed by the machine. It is understood by a virtual machine known as Java Virtual Machine or JVM. JVM contains a Java interpreter which converts the Bytecode into machine code of the target computer. JVM is platform specific i.e. each platform has its own JVM. But once the proper JVM is installed on the machine, it can run any Java Bytecode program. The below diagram illustrates this:

Question 5

Question 5How is traditional compilation process different from Java compilation process?

Accepted Answer

In traditional compilation process, the machine language code generated by the compiler is specific to the platform for which the source code is compiled. The executable file generated for one platform like Windows will not work on other platforms like Macintosh. In Java compilation process, the source code of a Java program is compiled to an intermediate binary code called the Bytecode. This Bytecode is interpreted and executed by JVM on the target platform. Bytecode is platform independent so the same Bytecode which is generated for one platform like Windows will work on other platforms like Macintosh without any modifications.

Question 6

Question 6What are JVM and JIT?

Accepted Answer

JVMJVM stands for the Java Virtual Machine. It is a virtual machine that runs Java programs and can be installed on several different operating systems such as Windows, UNIX, Macintosh etc. JVMs allow Java programs to run on almost any computer. A JVM processes instructions similar to a physical processor. However, the Java code (with "java" extension) must first be converted into Bytecode that the JVM understands.JITJIT is the Just-In-Time compiler included in the JVM that compiles selected portions of the Bytecode into executable codes to improve the execution performance.

Question 7

Question 7Distinguish between the following:a. Source code and Object code

Accepted Answer

Source CodeObject CodeIt is a set of instructions written in a high-level programming language.It is the compiler generated machine language version of the source code.It can be read and understood by humans.It is not human readable but is understood by machines.b. Compiler and InterpreterCompilerInterpreterIt converts the whole source program into the object program at once.It converts the source program into the object program, one line at a time.It displays the errors for the whole program together, after the compilation.It displays the error one line at a time and only after fixing that error the control goes to the next line.c. ".java" file and ".class" file".java" file".class" fileIt contains the Java source code of the program.It contains the Bytecode of the program.It is written by human (programmer)It is generated by Java compiler.

Question 8

Question 8What is Java Bytecode?

Accepted Answer

The programs written in Java are compiled into a machine language for a virtual computer called Java Virtual Machine (JVM). The machine language for this special Java Virtual Machine is called Java Bytecode. The Bytecode files are generated with the ".class" extension.

Question 9

Question 9Describe the slogan, "Write once, run anywhere" in relation to Java.

Accepted Answer

Bytecode and JVM makes Java programs platform independent. This is one of the most important and powerful features of Java. The Bytecode of a Java program can be run on any platform that has a corresponding JVM installed on it. No modifications to this Bytecode are required. Hence, it is said that Java provides "Write once, run anywhere" capabilities.

Question 10

Question 10Describe four features of Java.

Accepted Answer

Four features of Java are:Object Oriented — Java is an object-oriented programming language because it treats everything as an object. The entire program code and data resides within objects and classes. This enables us to easily use and extend the object model.Robust — Java is a robust and reliable programming language. It has strict compile time and runtime checking of data types. Memory allocation and de-allocation is automatic in Java, so there is less for the programmer to worry about.Platform Independent — The concept of "Write once, run anywhere", is one of the most important and powerful features of Java. Java applications can run on any platform that has a corresponding JVM installed on it.Simple — Java is simple and easy to learn programming language. The removal of many unreliable features of C and C++ (its predecessors) has simplified its understanding and implementation.

Introduction to Java