Introduction to PrimitivesOverviewPrimitivesintbyte and shortlongdoublefloatAn aside: approximationsGiving names to numbersVariablesDeclaring variablesGiving values to variablesNumber “width”Widening and narrowingCastsExample castsThe fifth integer typeMixed typesMath methodsMethod parametersThe EndJan 14, 2019Introduction to Primitives2OverviewToday we will discuss:The eight primitive types,especially int and doubleDeclaring the types of variablesOperations on primitivesThe assignment statementHow to print results3PrimitivesPrimitives are the “basic” data valuesThere are eight types of primitives:boolean -- used for true and false valueschar -- used for single characters (letters, etc.)byte, short, int, long -- four different kinds of integer (whole number) valuesfloat, double -- two different kinds of decimal numbers (numbers with a decimal point)4intThe most important integer type is intAn int is a “whole” number (no decimal point)Numbers occupy memory in the computerLarger numeric types require more memory byte: 1 byte short: 2 bytes int: 4 bytes long: 8 bytesAn int can be between about two billion (two thousand million) and negative two billionIf you just write a number, such as 25, Java assumes it is an intHence it is easier to work with int values than with the other integer types (byte, short, and long)Use int in preference to other integer types5byte and shortA byte can be between -128 and 127A short can be -32768 to 32767Why these numbers?These are “round numbers” in binary; for example, 0111 1111 1111 1111 is binary for 32767 1000 0000 0000 0000 is binary for -32768 The first bit is the sign bit: a 1 means it’s a negative numberUse byte or short only whenYou know the numbers are all smallThere are millions of numbers to remember6longlong integers are for when two billion isn’t large enough for your needsA long can be as long as about 19 digitsA long occupies twice as much space as an intArithmetic on long values is slowerUse long only when you need really big numbersA long number is written like an int, but with an L suffixExamples: 895000000000L, 25L, 5L, -123LEven larger numbers are available in Java--but they are objects, not primitives7doubleA double represents a “real” numberAlso sometimes called “floating point”These are numbers with a decimal pointIf you just write a real number, such as 1.37, Java assumes it is a doubleHence it is easier to work with double values than with float valuesdoubles can also be written using scientific notation, where E stands for “times ten to the power”Examples: 7.3E5 = 730000.0, 7.3E-5 = 0.000073A double can represent numbers in the range 4.9*10-324 to 1.8*10308 and has 15 or 16 digits of accuracyUse double in preference to float8floatfloat is the other kind of “real,” or “floating point” numberfloat has about 8 digits of accuracyArithmetic with float is not fasterUse float only to save space when there are millions of numbers involved A float constant is written like a double constant, but with an F suffixExamples: 1.23F, -9F, 6.7E14FA float can represent numbers in the range 1.4*10-45 to 3.4*1038 and has 6 or 7 digits of accuracy9An aside: approximationsIntegers are precise, but real numbers are always approximate (inaccurate)Computers always use the binary system internallyMany numbers that can be expressed precisely in decimal cannot be represented precisely in binaryFor example, the numbers 1.1, 1.2, 1.3, and 1.4 can only be approximated in binaryTwo numbers that look the same may actually be subtly differentNever test floating point numbers for equality!Only test for larger or smaller, or for “not larger” or “not smaller”This is not a Java rule—it’s a programming rule10Giving names to numbersSometimes you know what a number isYou have 10 fingersThere are 24 hours in a dayπ is 3.141592653589793238Numbers written like this are called literalsYou can use literals anyplace in Java that you can use a numberIt’s usually better to use names instead:classSize, myBankBalance, myAge, speedometerReadingA literal used without explanation is called a magic numberExample: e = 8.987551787E16 * m;Better: energy = speedOfLightSquared * mass;Better yet: final double C = 2.99792458E8; e = m * C * C;Style rule: Avoid magic numbers!Sometimes names are simply more convenient, for example,Math.PI instead of 3.14159265358979323811VariablesBefore you use a variable, you must declare it (tell Java what type it is: int, double, char, ...) There are two reasons for this:Different types require different amounts of spaceSo Java can prevent you from doing something meaningless (adding 5 and true, or multiplying two dates together)Before you use a variable, you must also define it (tell Java what value it has)It makes no sense to print out your bankBalance, or to add 100.00 to your bankBalance, if you don’t have a meaningful, well-defined initial value for bankBalance to start withYou might assign an initial value to your variable, or compute a value, or read a value in; but you have to get one somehow12Declaring variablesYou declare variables like this: int classSize; double myBankBalance;When you declare a variable to be a primitive type, Java automatically finds space for itThe amount of space Java needs to find depends on the type of the variableThink of a variable as a specially shaped “box,” designed to hold a value of a particular typeAn int variable is four bytes long and there’s a special place for the sign bitA float variable is also four bytes long, but the bits are used differently--some are used to tell where the decimal point goes13Giving values to variablesA variable is just a name for some valueYou have to supply the actual value somehowJava tries to prevent you from using a variable that you haven’t given a valueYou can assign values like this: classSize = 57; myBankBalance = 123.01; // no "$"!14Number “width”Numeric types are considered wider or narrower than other numeric typesThis is based partly on number of bytes occupiedAlso based on how large a number it can holdJava doesn’t mind if you assign a narrow value to a wide variable: int n = 3;Java is not happy if you