Notes on core java

1. Core Java
Debasish Pratihari
Java File Structure :

An optional package directive

Zero or more import directive

One or more Class definition
Java Keywords :
abstract
switch
package
if
double
byte
throws
return
int
final
class
volatile
super
continue
assert
synchronized
private
implements
else
case
transient
short
interface
finally
const *
while
for
default
boolean
this
protected
import
enum
catch
try
static
long
float
new
goto *
do
break
throw
public
instanceof
extends
char
void
strictfp
native
Note:
The * marked keywords
are reserved keywords.
They may be in action in
future.
Variable :


A variable is a named memory location that is
used to store information.
It is able to store data only of one particular
type
Literals :


Explicit data values present in the program.
Each literal is of a particular type.
Lecture/core/LF1/04
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2. Core Java
Debasish Pratihari
Identifier :







The name given for anything in java
Example- variable name, method name, class
name etc.
It must start with a letter, an underscore( _ ),
or dollar sign( $ ).
It can’t include operator of java.
Is case sensitive.
It must not be a java keyword.
White space is not allowed in identifiers
Primitive Types :

A primitive types is pre-defined by the language
and is named by reserved keywords.
Primitives Types in Java :
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3. Core Java
Debasish Pratihari
Default Values :
Note : Compilers never assign a value to local variables of
a class. So they must be initialized explicitly before use.
Examples of Literals :
25%
boolean flag = true;
char c = 'D';
byte b = 100;
short s = 10000;
int i = 100000;
Note:
 new keyword isn't used when initializing a variable
of a primitive type. Primitive types are special data
types built into the language

A literal is the source code representation of a fixed
value
Literals in the form of octal and Hexa :

The integral types (byte, short, int, and long)
can be expressed using decimal, octal, or
hexadecimal number systems.
Examples:
int value = 10;
int value = 012;
int value = 0x0a;
Lecture/core/LF1/04
// The number 10, in decimal
// The number 10, in octal
// Then number 10, in Hexadecimal
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4. Core Java
Debasish Pratihari
Operators :

Operators are special symbols that perform
specific operations on one, two, or three
operands, and then return a result.
Comments :

Comments should be used to give overviews of
code and provide additional information that is
not readily available in the code itself.
Comments should contain only information that
is relevant to reading and understanding the
program.
Java Comment Conventions :





Block comment
Single-Line Comment
Trailing Comment
End-of-Line Comment
Documentation Comment
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