Java Basic Elements Lecture on Computer Science

Outline
• Starting with Java
• Elements of Java
• Variables
• Constants
• Escape Sequences

Starting with Java
public static void main(String args[])
means you can call this method from any where .
keyword in java means you don't need object for this you can directly call it.
means this method is not returning any thing.
Name of the method
String args[], which is actually an array of String type, and it's name is args
here. args[] is for passing arguments to your program.

Elements of Java
• Java programs are a collection of
1. Whitespace
2. Identifiers
3. Comments
4. Literals
5. Operators
6. Separators, and
7. Keywords
• Whitespace in Java is used to
separate the tokens in a Java source
file.
• In Java, whitespace is a space, tab, or
newline.
• Java Literals are syntactic
representations of Boolean,
character, numeric, or string data.
Literals provide a means of
expressing specific values in your
program.
• An identifier is any name in a Java
program. Identifiers are used to
denote classes, methods, variables
and labels.
• An identifier may be any descriptive
sequence of uppercase and
lowercase
• letters, numbers, or the underscore
and dollar-sign characters.
• Java is case-sensitive.
• Valid: AvgTemp, count, a4, $test,
this_is_ok
• Invalid: 2count, high-temp, Not/ok
• Comments are portions of the code
ignored by the compiler which allow
the user to make simple notes in the
relevant areas of the source code.
Comments come either in block form
or as single lines.
1
2
3
4

Elements of Java (Cont.)
5. Operators: Operators are used to perform operations on variables and values.
Arithmetic
Operator Name Description Example
+ Addition Adds together two values x + y
- Subtraction Subtracts one value from another x - y
* Multiplication Multiplies two values x * y
/ Division Divides one value by another x / y
% Modulus Returns the division remainder x % y
Increment and Decrement Operators
++ Increment Increases the value of a variable by
1
++x
-- Decrement Decreases the value of a variable by
1
--x
Assignment Operator
Operator Example Same As
= x = 5 x = 5
+= x += 3 x = x + 3
-= x -= 3 x = x - 3
*= x *= 3 x = x * 3
/= x /= 3 x = x / 3
%= x %= 3 x = x % 3
Bitwise Operators
Operator Description Example Same as Result Decimal
& AND - Sets each bit to 1 if both bits are 1 5 & 1 0101 & 0001 0001 1
| OR - Sets each bit to 1 if any of the two bits is 1 5 | 1 0101 | 0001 0101 5
~ NOT - Inverts all the bits ~ 5 ~0101 1010 10
^ XOR - Sets each bit to 1 if only one of the two bits is
1
5 ^ 1 0101 ^ 0001 0100 4
<< Zero-fill left shift - Shift left by pushing zeroes in
from the right and letting the leftmost bits fall off
9 << 1 1001 << 1 0010 2
>> Signed right shift - Shift right by pushing copies of
the leftmost bit in from the left and letting the
rightmost bits fall off
9 >> 1 1001 >> 1 1100 12
>>> Zero-fill right shift - Shift right by pushing zeroes in
from the left and letting the rightmost bits fall off
9 >>> 1 1001 >>> 1 0100 4
Comparison Operators
Operator Name Example
== Equal to x == y
!= Not equal x != y
> Greater than x > y
< Less than x < y
>= Greater than or equal to x >= y
<= Less than or equal to x <= y
Logical Operators
&& Logical and Returns true if both statements are true x < 5 && x < 10
|| Logical or Returns true if one of the statements is
true
x < 5 || x < 4
! Logical not Reverse the result, returns false if the
result is true
!(x < 5 && x < 10)

5. Operators: Operators are used to perform operations on variables and values.
– Unary
• Require only one operand; they perform various operations such as
incrementing/decrementing a value by one, negating an expression, or inverting the value of
a Boolean.
– Ternary
• The conditional operator or ternary operator ?: is shorthand for the if-then-else statement.
The syntax of the conditional operator is:
variable = Expression ? expression1 : expression2

– Operator Precedence

Elements of Java
• Separators: Separators help define the structure of a program.
Symbol Name Purpose
() Parentheses Used to contain lists of parameters in method definition and
invocation. Also used for defining precedence in expressions,
containing expressions in control statements, and surrounding cast
types.
{} Braces Used to contain the values of automatically initialized arrays.
Also used to define a block
of code, for classes, methods, and local scopes.
[] Brackets Used to declare array types. Also used when dereferencing array
values.
; Semicolon Terminates statements.
, Comma Separates consecutive identifiers in a variable declaration. Also
used to chain statements together inside a for statement.
. Full-stop Used to separate package names from subpackages and classes. Also
used to separate a variable or method from a reference variable.

Elements of Java
• Keywords(Java Reserved Keywords): Java has a set of keywords that are reserved
words that cannot be used as variables, methods, classes, or any other identifiers.

Variables
• Variable is a name of memory location. There are three types of variables in java:
local, instance and static.
• Types of Variable: There are three types of variables in java:
– local variable: A variable which is declared inside the method is called local variable.
– instance variable: Instance variables in Java are non-static variables which are defined in
a class outside any method, constructor or a block. Each instantiated object of the class
has a separate copy or instance of that variable. An instance variable belongs to a class.
– static variable: A static variable is common to all the instances (or objects) of the class
because it is a class level variable. In other words you can say that only a single copy of
static variable is created and shared among all the instances of the class.

Variables - Example
• Example to understand the types of variables in java
class A
{
int data=50;//instance variable
static int m=100;//static variable
void method()
{
int n=90;//local variable
}
}//end of class

Constants
• A constant is a variable whose value cannot change once it has been assigned.
• Java doesn't have built-in support for constants.
• Syntax: modifier final dataType variableName = value; //global
constant
• For a simple floating point value (a number with a fractional part) like Pi, it would
look something like:
private static final double PI = 3.1415926;

Escape Sequences
• A character preceded by a backslash () is an escape sequence and has a special
meaning to the compiler.
Sequence Name Meaning
n New line Moves to beginning of next line
b Backspace Backs up one character
t Horizontal tab
Moves to next tab position
Tab spacing is every 8 columns starting with 1.
(Columns 9, 17, 25, 33, 41, 49, 57, 65, 73 ...)
Backslash Displays an actual backslash
' Single quote Displays an actual single quote
" Double quote Displays an actual double quote

References
• https://www.edx.org/learn/java
• https://www.infoworld.com/article/2076075/core-java-learn-java-from-the-grou
nd-up.html
• https://www.geeksforgeeks.org/java-how-to-start-learning-java/
• https://www.geeksforgeeks.org/jvm-works-jvm-architecture/
• https://beginnersbook.com/2013/05/jvm/
• https://www.iare.ac.in/sites/default/files/lecture_notes/IARE_OOPS_THROUGH_
JAVA_LECTURE_NOTES.pdf
• https://lecturenotes.in/notes/23198-note-for-object-oriented-programming-usin
g-java-oopj-by-debasish-pradhan?reading=true
• https://www.softwaretestinghelp.com/java/java-introduction-installation/

Java Basic Elements Lecture on Computer Science

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