Thursday, September 22, 2011

Learn Core JAVA in Easy Steps [Page 3]




JAVA Data Types :-
(1) Primitive :
1. Integral 
2. Boolean 
3. Floating 
(2) Reference :
1. Object 
2. String



  • byte: The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.
  • short: The short data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.
  • int: The int data type is a 32-bit signed two's complement integer. It has a minimum value of -2,147,483,648 and a maximum value of 2,147,483,647 (inclusive). For integral values, this data type is generally the default choice unless there is a reason (like the above) to choose something else. This data type will most likely be large enough for the numbers your program will use, but if you need a wider range of values, use long instead.
  • long: The long data type is a 64-bit signed two's complement integer. It has a minimum value of -9,223,372,036,854,775,808 and a maximum value of 9,223,372,036,854,775,807 (inclusive). Use this data type when you need a range of values wider than those provided by int.


  • float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in section 4.2.3of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead.Numbers and Strings covers BigDecimal and other useful classes provided by the Java platform.
  • double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in section4.2.3 of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.
  • boolean: The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.
  • char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65,535 inclusive).

    Data TypeDefault Value (for fields)
    byte0
    short0
    int0
    long0L
    float0.0f
    double0.0d
    char'\u0000'
    String (or any object)  null
    booleanfalse



Learn Core JAVA in Easy Steps [Page 2]





The Features / Buzz Words / Characteristics / Advantages of JAVA:

  1. Simple
  2. Secure
  3. Platform Independent
  4. Portable
  5. Object Oriented
  6. Robust
  7. Distributed
  8. Dynamic
  9. High Performance
  10. Multithreaded
  11. Interpreted
  12. Architecture Neutral

Object Oriented:
  • Inheritance
  • Encapsulation
  • Polymorphism
  • Abstraction/Dynamic binding


How to Create and Execute a Program in Core Java:


there are two ways:
1. without Integrated Development Environment (IDE)
2. with Integrated Development Environment (IDE)


1.without IDE


Create: write your program in notepad and save it with .java extension.
[make sure that all class names are starting with capital letter and your filename must be the classname which has the main method]


Execute: open command prompt and write javac filename.java [this will compile your java file] then write java filename [this will run your compiled file].


2.with IDE


Eclipse and NetBeans are most popular IDEs for JAVA.
[as we have TC-Turbo C in C and C++]



Wednesday, September 21, 2011

Learn Core JAVA in Easy Steps [Page 1]



Book: The JAVA Language Specification


James A. Gosling, OC (born May 19, 1955 near Calgary, Alberta, Canada) is a software developer. Between 1984 and 2010, Gosling was with Sun Microsystems, best known as the father of the Java programming language.


Java can run on any Hardware and Software interface.


A program coded in Java is compiled by Java Compiler (javac) - JDK (Java Development Kit) and it creates a machine independent byte code (.class file) which we can run by using JVM (Java Virtual Machine) which has a compiler named JIT (just-in-time).


Three types of JAVA programs/softwares/applications :


1. Standalone/Simple Applications
2. Applets
3. Servlets (and jsp) - Web Applications