Casting, Expression and Operators

Java Typecasting:

• Typecasting is when you assign a value of one primitive data type to another type.
• Casting refers to the conversion of one data type to another. 
• When we cast a particular variable, the data type of the variable itself is not altered. 
• For example:
• int num1=3, num2=4;
• double result = (double) num1 / num2;
• When we cast, num1 to a double.
• The variable num1 does not change its data type from int to double. 
• Instead, a new copy of num1 is made and its data type is changed to double.
• For Example: 
• A. Upcasting & Downcasting
• B. Implicit & Explicit casting
• 1. Upcasting: 
• When we cast a variable to a higher data type it is known as upcasting.
• such as...
• byte -> short, int, long, float, double
• short -> int, long, float, double
• char -> int, long, float, double
• int -> long, float, double
• long -> float, double
• float -> double
• For example:
• int is a higher data type than short.
• int is 32 bits memory allocated while short which is 16 bits.
• 2. Downcasting: 
• When we cast a variable to a lower data type, it is known as downcasting. 
• Such as...
• byte -> char
• short -> byte, char
• char -> byte, short
• int -> byte, short, char
• long -> byte, short, char, int
• float -> byte, short, char, int, long
• double -> byte, short, char, int, long, float
• For Example:
• short a = 347;
• int d = (short) b;
• System.out.println(a);
• System.out.println(d);
• 3. Implicit - converting a smaller type to a larger type size

• It is automatically converted.
• When any casting that is performed by the compiler, it is known as implicit casting. 
• It is also called as Widening casting.
• byte > short > char > int > long > float > double

For Example:
int myInt = 9;
double myDouble = myInt;

For Example:
int a=3;
long b=4;
long c=a+b; // a is implicitly cast to a long

Program:
public class Conversion{
public static void main(String[] args)
{
int i = 200;
  //automatic type conversion
long l = i;
  //automatic type conversion
float f = l;
System.out.println("Int value "+i);
System.out.println("Long value "+l);
System.out.println("Float value "+f);
}

}

• 4. Explicit - converting a larger type to a smaller size type
• It is manually converted.
• When casting is performed by the programmer using the cast operator (), it is known as explicit casting. 
• It is also called as Narrowing casting.
• double > float > long > int > char > short > byte

For Example:
double myDouble = 9.78;
int myInt = (int) myDouble;

For Example:
char c='A';
int s=1;
short ans= (short) (c+s);

Program:
public class Narrowing
{
public static void main(String[] args)
{
double d = 200.06;
//explicit type casting
long l = (long)d;
//explicit type casting
int i = (int)l;
System.out.println("Double Data type value "+d);
//fractional part lost
System.out.println("Long Data type value "+l);
//fractional part lost
System.out.println("Int Data type value "+i);
}

}

Expression:

• Expressions are built using values, variables, operators and method calls.
• For Example: (a * 2)
• You can write a simple expression into a statement by adding a semi-colon.
• For Example: (a * 2);

Types of Expression:

• 1. Produce a value:
• For Example: (r*r)
• 2. Assign a value:
• For Example: area = pi * (r*r)

Operators:

• It is a symbol that is used to perform operations.
• Operators are used to perform operations on variables and values.
• For example, + is an operator that performs addition.
• For Example: 10 + 20
• There are mainly three types:
• A. Unary Operators
• Unary operator means only one operator and one operand.
• For Example Assignment Operator
• B. Binary Operators
• Binary operator means two operands and one operator.
• For Example Arithmetic Operator
• C. Ternary Operators
• Ternary operator means three operands and two operators
• For Example Ternary Operator

Types of operators:

• 1. Arithmetic operators
• Arithmetic operators are used to perform mathematical operations like +, -,*, etc.
• For Example:

+ Addition (also used for string concatenation)
- Subtraction Operator
* Multiplication Operator
/ Division Operator
% Remainder Operator

• For Example:

double number1 = 12.5, number2 = 3.5, result;
result = number1 + number2;

• 2. Assignment operators
• Assignment operators are used in Java to assign values to variables.
• For Example int age;

age=101;

• The assignment operator assigns the value on its right to the variable on its left.
• The other type of assignment operator is called a shorthand assignment.
• For Example:

Operator Example Equivalent to
+= x += 5 x = x + 5
-= x -= 5 x = x - 5
*= x *= 5 x = x * 5

• 3. Comparison or Relational operators
• This operator determines the relationship between the two operands. 
• It checks if an operand is >, <, ==, != and so on. 
• Depending on the relationship, it results to either true or false.
• For Example:

Operator Description Example
== equal to 5 == 3 is evaluated to false
!= not equal to 5 != 3 is evaluated to true
> greater than 5 > 3 is evaluated to true
< less than 5 < 3 is evaluated to false
>= greater than or equal to 5 >= 5 is evaluated to true
<= less then or equal to 5 <= 5 is evaluated to true

• 4. Logical operators
• It is used to apply a logical condition. 
• A. OR Operator (||)
• conditional-OR; true if either of the boolean expression is true
• For Example, false || true is evaluated to true
• B. AND Operator (&&)
• conditional-AND; true if all boolean expressions are true
• For Example, false && true is evaluated to false

• 5. Bitwise operators
• To perform bitwise and bit shift operators in Java, these operators are used.
• For Example:

Operator Description
~ Bitwise Complement
<< Left Shift
>> Right Shift
>>> Unsigned Right Shift
& Bitwise AND
^ Bitwise exclusive OR
| Bitwise inclusive OR

• 6. Unary operators
• Unary operator performs operation on only one operand.
• For Example:

Operator Meaning
+ Unary plus
- Unary minus
++ Increment operator; increments value by 1
-- decrement operator; decrements value by 1
! Logical complement operator

• 7. instanceof Operator
• Instance of the operator is used for type checking. 
• It can be used to test if an object is an instance of a class, a subclass or an interface.
• For Example:

String name= "Sarthak";
boolean result;
result = name instanceof String;

• When you run the program, the output will be true. 
• It's because the name is the instance of String class.

• 8. Ternary Operator
• The conditional operator or ternary operator ?: is shorthand for if-then-else statement. 
• Syntax: variable = Expression ? expression1 : expression2
• If the Expression is true, expression1 is assigned to variable.
• If the Expression is false, expression2 is assigned to variable.
• For Example:

int februaryDays = 29;
String result;
result =  (februaryDays == 28) ? "Not a leap year" : "Leap year";