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Explain Features of Java - Introduction

1) Simple
• Similar to C/C++ in syntax
• But eliminates several complexities of
– No operator overloading
– No direct pointer manipulation or pointer arithmetic
– No multiple inheritance
– No malloc() and free() – handles memory automatically
– Garbage Collector
• Lots more things which make Java more attractive.
2) Object-Oriented
• Fundamentally based on OOP
– Classes and Objects
– Uses a formal OOP type system
– Lends an inherent structure/organization for how wewrite Java programs
• Unlike spaghetti code in languages like Perl
– Efficient re-use of packages such that the programmeronly cares about the interface and not the implementation
3) Distributed / Network Oriented
• Java grew up in the days of the Internet
– Inherently network friendly
– Original release of Java came with Networking libraries
– Newer releases contain even more for handlingdistributed applications
• RMI, Transactions
4) Robust / Secure / Safe
• Designed with the intention of being secure
– No pointer arithmetic or memory management!
– The JVM “verifier”
• Checks integrity of byte-codes
– Dynamic runtime checking for pointer and array access
• No buffer overflow bugs!
– SecurityManager to check which operations a piece ofcode is allowed to do
– “Sandbox” operation for applets and other untrustedcode
• Limited set of operations or resources made available
• Contrast to ActiveX
5) Portable
• “Write-Once Run-Anywhere”
• The Java Virtual Machine becomes the common denominator
– Bytecodes are common across all platforms
– JVM hides the complexity of working on a particularplatform
• Difficult to implement a JVM
• But simpler for the application developer
• Java does this well
6) High-Performance
• Java performance IS slower than C
• Tradeoff between development time vs. run time
• Additional checks in Java which make is secure androbust and network aware etc, all have a small cost.
– JIT compilation and HotSpot
• Dynamic compilation of bytecode to native code atruntime to improve performance
– HotSpot optimizes code on the fly based on dynamicexecution patterns
• Can sometimes be even faster than compiled C code!
7) Multi-Threaded
• Native support for threading
– We will cover this in a lot of detail
• Basic concept
– The ability to have multiple flows of control/programswhich appear to run at the same time
• Processes - application level
• Threads – within the application
– JVM uses native threads on operating system butprovides a consistent abstraction for the developer.
8) Dynamic
• Java is “self-aware”
– Java code can look at itself and tell what interfaces itexports (Introspection)
– Can dynamically load new classes/code at runtime
9) Java Programmer Efficiency
• Faster Development
– More programmer friendly
– Less error prone
– Easier to manage large development projects
• Robust memory system
– No pointer arithmetic and manual memory management.Garbage collector!
• Libraries
– Re-use of code

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Question 1. Which of the following is least like the others?
A.    cube
B.    sphere
C.    pyramid
D.    circle

D (because the circle is the only two-dimensional figure)

Question 2. Consider a language which uses the following set of characters:
Small set: { a b c }
Large set: { A B C }
Punctuation set: { x y }
This language must follow the following rules:
  1.    A punctuation character must end all series.
  2.    A series can have up to but no more than 4          characters,including punctuation characters.

Does the following series follow all the rules of the language defined above?
  A.    Yes
  B.    No

A (the series has only four characters and ends in a punctuation character)

Question 3. Consider the following flow chart for a customer:

The person in No.1 is:
    A.   Married, with children
    B.   Married, with at least one son
    C.   Unmarried, with at least one daughter
    D.   Unmarried, with at least one son
    E.   Unmarried, with no children