Presentation on theme: "Primitive Data Types There are a number of common objects we encounter and are treated specially by almost any programming language These are called basic."— Presentation transcript:
1 Primitive Data TypesThere are a number of common objects we encounter and are treated specially by almost any programming languageThese are called basic (primitive) objects, such as integers etcE.g., Java predefines classes for such basic typesfor example, one predefined class is Integer:To create an Integer (object): Integer wagePerHour = new Integer(10); System.out.println( wagePerHour );
2 Primitive Data TypesAlthough in pure object-oriented languages (such as Smalltalk and Ruby), we can consider everything as objects and defines everything as class, for efficiency, some languages like C++ and Java treat common objects such as numbers, characters, and logical values specially, and introduces them into the language as primitive data typesNote: this division between primitive types and objects is disliked by some programmers familiar with languages such as Smalltalk and Ruby where everything is an object
3 Primitive Data Types There are exactly eight primitive data types four of them represent integers:byte, short, int, longtwo of them represent floating point numbersfloat, doubleone of them represents characters:charand one of them represents boolean (logical) values:boolean
4 Numeric Primitive Data Types byte, short, int, long, float, and double are numeric data typesThe difference among the various numeric primitive types is their storage sizes and representations, and therefore the ranges and precision of the values they can storeTo understand this, we need to have a rough understanding of computer memory storage
5 MemoryPrimary storage area for programs and dataAlso called RAMRAM is divided into many cells; each cell can be identified by a numeric addressMainMemoryEach memory cell has a set number of bits (usually 8 bits, or one byte); a bit can represent 2 values)927892799280928192829283928492859286- how many values can a byte represent?A computer can use more cells to store data, e.g., 2 bytes- how many values can 2 bytes represent?
6 Numeric Primitive Data “Objects” of different numeric data types occupy different number of cellsTypebyteshortintlongfloatdoubleStorage8 bits16 bits32 bits64 bitsMin Value-128-32,768-2,147,483,648< -9 x 1018+/- 3.4 x 1038 with 7 significant digits+/- 1.7 x with 15 significant digitsMax Value12732,7672,147,483,647> 9 x 1018IEEE 754 format
7 Characters A char is a single character from a character set A character set is an ordered list of characters; each character is given a unique numberCharacter literals are represented in a program by delimiting with single quotes:'a‘ 'X‘ '7' '$‘ ',' '\n'
8 Character Sets The ASCII character set is quite popular. It includes: uppercase letterslowercase letterspunctuationdigitsspecial symbolscontrol charactersA, B, C, …a, b, c, …period, semi-colon, …0, 1, 2, …&, |, \, …carriage return, tab, ...
9 Boolean A boolean value represents logical value: true or false The reserved words true and false are the only valid values for a boolean typeA boolean can also be used to represent any two states, such as a light bulb being on or off
10 Multiple variables can be created in one declaration Variables: RevisitedWe already know that a variable must be declared, specifying the variable's name and the type of information that will be held in itAs of now, think of a variable as a name for a location in memory cell (we will revisit the concept later)int total;int count, temp, result;Multiple variables can be created in one declarationdata typevariable name
11 Variables A variable can be given an initial value in the declaration int sum = 0;int base = 32, max = 149;String msg1 = new String( “Hello” );String msg2 = “Hello” ;When a variable is referenced in a program, its current value is used
12 Change the Value of a Variable: Assignment Statement An assignment statement changes the value of a variableThe assignment operator is the = signtotal = 55;The expression on the right is evaluated and the result is stored in the variable on the leftThe value that was in total is overwrittenRemember: you can only assign a value to a variable that is consistent with the variable's declared type
13 ConstantsA “constant variable” is an identifier that is similar to a variable except that it holds one value for its entire existenceWhy constants:give names to otherwise unclear literal valuesfacilitate changes to the codeprevent inadvertent errorsThe compiler will issue an error if you try to assign value to a constant variable after its declaration
14 Arithmetic Expressions An expression is a combination of operators and operandsArithmetic expressions (we will see logical expressions later) are essentially special methods applied to numerical data objects: compute numeric results and make use of the arithmetic operators:Addition +Subtraction -Multiplication *Division /Remainder %
15 Division and Remainder If both operands to the division operator (/) are integers, the result is an integer (the fractional part is discarded)14 / equals?8 / equals?The remainder operator (%) returns the remainder after dividing the second operand into the first14 % equals?8 % equals?