Download - Data Types Operators Expressions_3
CT038-3-2 Object Oriented Development with
Java
Data Types, Operators and Expressions
CT038-3-2 OODJ Data types, Operators and Expressions
Topic & Structure of the lesson
• Introduction
• Constants
• Variables
• Data Types
• Operators
• Expressions
CT038-3-2 OODJ Data types, Operators and Expressions
Learning outcomes
• At the end of this lecture you should be able to:
• Identify data types, operators and expressions.
CT038-3-2 OODJ Data types, Operators and Expressions
Key terms you must be able to use
• If you have mastered this topic, you should be able to use the following terms correctly in your assignments and exams:
• Constants
• Variables
• Data types
• Operator
CT038-3-2 OODJ Data types, Operators and Expressions
Introduction
• A programming language is designed to process certain kind of data consisting of numbers, characters and strings and to provide useful output as information.
• Every program instruction must conform precisely to the syntax rules of the language.
CT038-3-2 OODJ Data types, Operators and Expressions
Constants
• Constants in Java refer to fixed values that do not change during the execution of a program.
• In Java constant are identified with the keyword final.
CT038-3-2 OODJ Data types, Operators and Expressions
Syntax - Constant
•In a method:final typeName variableName = expression;
•In a class:accessSpecifier static final typeName variableName = expression;
Example:
final double NICKEL_VALUE = 0.05;
public static final double LITRES_PER_GALLON = 3.785;
CT038-3-2 OODJ Data types, Operators and Expressions
Variables
• A variable may take different values at different times during the execution of the program
CT038-3-2 OODJ Data types, Operators and Expressions
Syntax - Variable
typeName variable Name = value;
Or
typeName variable Name;
Example
String greeting = “ Hello Java”;
CT038-3-2 OODJ Data types, Operators and Expressions
Data Types
• Every variable in Java has a data type.
• Data types specify the size and type of values that can be stored.
CT038-3-2 OODJ Data types, Operators and Expressions
Data Types in Java
Primitive Non Primitive
Numeric Non-numeric
Integer Floating point Character Boolean
Classes Arrays
Interface
CT038-3-2 OODJ Data types, Operators and Expressions
Integer Type
• Integer types can hold whole numbers.
• Java supports signed values, meaning they can be both positive and negative.
CT038-3-2 OODJ Data types, Operators and Expressions
Size and Range of Integer Types
Type Size Min value Max value
byte One byte -128 127
short Two bytes
-32 786 32 767
int Four bytes
-2 147 483 648 2 147 483 647
long Eight bytes
- 9 223 372 036 854 775 808
9 223 372 036 854 775 807
CT038-3-2 OODJ Data types, Operators and Expressions
• Wider data types require more time for manipulation.
• So it is advisable to use smaller data types, wherever possible.
CT038-3-2 OODJ Data types, Operators and Expressions
Floating Point Type
• Integer can only hold whole numbers.
• So we use floating point type to hold numbers containing fractional parts.
• Example : 25.79 and -1.37
Floating Point
Float Double
CT038-3-2 OODJ Data types, Operators and Expressions
Size and Range of Floating Point Types
Type Size Min Value Max Value
float 4 bytes 3.4e-0.38 3.4e+038
double 8 bytes 1.7e-0.38 1.7e+038
CT038-3-2 OODJ Data types, Operators and Expressions
Character Type
• The character type, representing code units in the Unicode encoding scheme.
• The char type assumes a size of 2 bytes.
• It can hold only a single character.
• Example
char c = ‘X’ ;
CT038-3-2 OODJ Data types, Operators and Expressions
Boolean Type
• Boolean type is used when we want to test a particular condition during the execution of the program.
• There are only two values that a boolean type can take: true or false
• Both these words are Java keywords.• boolean type uses one bit of storage.
CT038-3-2 OODJ Data types, Operators and Expressions
Operators
• An operator is a symbol that tells the program to perform certain mathematical or logical manipulations.
CT038-3-2 OODJ Data types, Operators and Expressions
Java operators are classified into:
• Arithmetic operators
• Relational operators
• Logical operators
• Bitwise operators
• Conditional operators
• Increment and decrement operators.
CT038-3-2 OODJ Data types, Operators and Expressions
Expressions
• Expressions are evaluated using an assignment statement in the form
variable = expression;• When the statement is encountered, the
expression is evaluated first and the result then replaces the previous value of the variable on the left side.
CT038-3-2 OODJ Data types, Operators and Expressions
• Example :
x = a*b-c
The variables a,b and c must be declared before they are used in the program.
CT038-3-2 OODJ Data types, Operators and Expressions
Type Conversions in Expressions
• Java permits mixing of constants and variables of different types in an expression.
• The final result of an expression is converted to the type of the variable on the left of the assignment.
CT038-3-2 OODJ Data types, Operators and Expressions
Casting a Value
• Example
• Consider the calculation of ratio of girls to boys in this class.ratio = girls_number / boys_number
• girls_number and boys_number are declared as integer in the program.
• But there is possibility of the ratio to be a floating number.
CT038-3-2 OODJ Data types, Operators and Expressions
• This problem can be solved by converting locally the variables to the floating point as shown below.
ratio = (float)girls_number / boys_number
• The operator (float) converts girls_number to floating point.
CT038-3-2 OODJ Data types, Operators and Expressions
Use of Casts
Examples Actionx = (int)7.5 7.5 is converted to integer
a = (int) 21.3 / (int)4.5 Evaluated as 21 / 4
b = (double) sum/n Division done in floating point mode
y = (int)(a+b) The result of (a+b) is converted to integer.
z = (int)a + b a is converted to integer then added to b
CT038-3-2 OODJ Data types, Operators and Expressions
Summary
• Java has eight primitive types, including four integer types and two floating point types.
• A final variable is a constant. Once the value is set, it cannot be changed.
• You can use cast type to convert a value to different type.