Multiple Choice Questions
Java applications ...........
- Are platform dependent
- Don't need a platform to run
- Are platform independent ✓
- Can't run on Windows
JVM stands for ...........
- Java Visual Monitor
- Java Video Monitor
- Java Virtual Monitor
- Java Virtual Machine ✓
JRE stands for ...........
- Java Runtime Editor
- Java Runtime Environment ✓
- Java Runtime Expression
- Java Runtime Enabler
Stand-alone Java applications ........... for execution.
- Need Java-compatible web browser
- Need an assembler
- Don't need Java-compatible web browser ✓
- Need a linker
Java uses ........... for execution.
- Compiler and interpreter ✓
- Interpreter only
- Compiler only
- None of these
A program that translates code written in a high-level language into machine code is called ...........
- Compiler ✓
- None of these
A program that translates an assembly language program into machine code is called a/an ...........
- Assembler ✓
- None of these
Java is ...........
- Object oriented
- All of these ✓
Java can be used to write ...........
- Stand-alone applications only
- Both stand-alone and internet applications ✓
- Internet applications only
- None of these
Java applications can run on ...........
- Windows platform
- Macintosh platform
- UNIX platform
- All of these ✓
State whether given statements are True or False
Stand-alone Java applications cannot run independently on a computer.
A console based Java application is designed to be used via a text-only interface.
Java Applets are Java applications that run within a web browser.
The machine language version of the source code generated by the compilation process is specific to the processor you are compiling on.
The Bytecode files are generated with the ".java" extension.
Java uses a combination of compilation and interpretation.
Just-In-Time (JIT) compiler compiles selected portions of Bytecode into executable code.
An interpreter translates the source code instructions into machine code all at once.
JVM stands for Java Virtual Monitor.
Machine language for JVM is called Bytecode.
Write a short note on types of Java programs.
There are two types of Java programs — Java Stand-Alone Applications and Java Applets.
Java Stand-Alone Applications
A 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 applications
b. Graphical User Interface based applications
Java 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.
How is Java platform independent?
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.
Describe the traditional compilation process with a suitable diagram.
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:
Describe the Java compilation process with a suitable diagram.
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:
How is traditional compilation process different from Java compilation process?
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.
What are JVM and JIT?
JVM 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.
JIT 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.
Distinguish between the following:
a. Source code and Object code
|Source Code||Object Code|
|It 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 Interpreter
|It 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" file|
|It 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.|
What is Java Bytecode?
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.
Describe the slogan, "Write once, run anywhere" in relation to Java.
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.
Describe four features of Java.
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.