Java Lecture1

Language Fundamentals 

1. Identifiers 

2. Reserve words 

3. data types 

4. Literals

5. Arrays

6. Types of variables

7. var-args method 

8. main method 

9. command line arguments

10. java coding standard

--------------------

1. Identifiers 

 

a name in java program is called identifiers, which can be used for identification purpose it can be method name, class name, variable name or label name.

class Test#1#

{

public static void main#2#(String#3# ar#4#[])

{

int x#5#=10;

}

}

in this how many identifiers are there???

Rules for defining java identifiers 

1. the only allowed character in java identifiers are ---> a to z, A to Z, 0 to 9, $ and _ if we are using any other character we will get compile time error.

example 

total_number valid

total#    invalid

2.identifiers cant starts with digit

total123 valid , 123total invalid 

java identifiers are case sensitive offcourse java language itself considered as case sensitive programming language.

Example: --

class Test

{

int number= 10;

int Number =20;

int NUMBER=30;

}

we can differentiate with respect to case.

4. there is no length limit for java identifiers

but it is not recommended to take too lengthy identifiers 

5. we cant use reserved word as identifiers 

int x =10; valid

int if=20; invalid

6. all predefined java class name and interface names we can use as identifiers

Example:

class Test

{

public static void main(String ar[])

{

int String =888;

SOP(String); //valid

int Runnable = 999;

SOP(Runnable); //valid

}

}

even though it is valid but it is not a good programming practice because it reduces readability and creates confusion.

which of the following are valid java identifiers?

total_number

total#   // invalid

123total  // invalid

total123

ca$h

_$_$_$_$_$

all@hands // invalid

java2share

Integer  

Int

int // invalid

==================================

Reserved words 

In java some words are reserved to represent some meaning or functionality such type of words are called reserved words.

total 53 reserved words 

3  reserved literals(true, false,null)

2 unused keywords(goto, const)

48 used keywords --- if, else, for, int.....

keywords for datatypes 

byte, short, int, float, long, double, boolean, char(8)

keywords for flow control

if, else, switch, case, default, while, do, for, break, continue, return(11)

keywords for modifiers

public, private, protected, static, final, abstract, synchronized, native, strictfp, transient, volatile(11)

keywords for exception handling

try, catch, finally, throw, throws, assert(6)

class related keywords

class, interface, extends, implements, package, import(6)

object related keywords

new, instanceof, super, this(4)

other keywords

void - return type keywords(if any method wont return anything)

in java return type is mandatory if a method wont return anything then we have to declare that method with void return type but in c language return type is optional and default return type is int

unused keywords

goto - uses of goto created several problems in old languages and hence sun people banned this keyword in java

& const - use final instead of const 

Note: goto and const are unused keywords and if we are trying to use we will get compile time error.

Reserved laterals:

true

false   // values for Boolean data types

null  // default value for object reference

enum keyword

we can use enum to defined a group of named constants 

enum month{

jan, feb, march.....dec;

} 

========================

conclusion 

1. all 53 rserved words in java contains only lowercase alphabet symbols

2. in java we have only new keyword and there is no delete keyword in java because destruction of useless objects is the responsibility of garbage collector.

3. the following are new keywords in java - strictfp, assert, enum