Friday, September 23, 2011
Thursday, September 22, 2011
JAVA Data Types :-
(1) Primitive :
(2) Reference :
- byte: The
bytedata 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
bytedata type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of
intwhere 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
shortdata 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
shortto save memory in large arrays, in situations where the memory savings actually matters.
- int: The
intdata 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: The
longdata 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
- float: The
floatdata 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
short, use a
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
BigDecimaland other useful classes provided by the Java platform.
- double: The
doubledata 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
booleandata type has only two possible values:
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
chardata 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 Type Default Value (for fields) byte 0 short 0 int 0 long 0L float 0.0f double 0.0d char '\u0000' String (or any object) null boolean false
The Features / Buzz Words / Characteristics / Advantages of JAVA:
- Platform Independent
- Object Oriented
- High Performance
- Architecture Neutral
- 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)
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].
Eclipse and NetBeans are most popular IDEs for JAVA.
[as we have TC-Turbo C in C and C++]
Wednesday, September 21, 2011
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
3. Servlets (and jsp) - Web Applications