ee2e1 lecture 1

8/4/2019 EE2E1 Lecture 1

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EE2E1. JAVA Programming

Lecture 1Lecture 1

From C to JavaFrom C to Java a one way ticket!a one way ticket!


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Contents A simple Java programA simple Java program

Data typesData types

VariablesVariables

Assignment/initializationAssignment/initialization

OperatorsOperators

Control FlowControl Flow StringsStrings

ArraysArrays


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Simple example Java programpublic class firstProgram

{

public static void main(String[] args){

System.out.println(Java is fun!);

}

}


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Main points

EverythingEverythingin a Java program is a classin a Java program is a class

KeywordKeywordpublicpublic is anis an access modifieraccess modifier

Program starts execution from theProgram starts execution from the mainmain methodmethod We will worry about whatWe will worry about whatstatic voidstatic voidmeans latermeans later

The program prints the string Java is fun!The program prints the string Java is fun!

System.out.println()System.out.println() means call themeans call the println()println()

method of the objectmethod of the object System.outSystem.out(which is part of(which is part of

the classthe class System)System)


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Data types Like C, Java is strongly typedLike C, Java is strongly typed

Java has 8 primitive data typesJava has 8 primitive data types

Machine independent storage requirementsMachine independent storage requirements


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Primitive data types

TypeType Storage requirementStorage requirement RangeRange

intint 4 bytes4 bytes --2,147,483,648 ..2,147,483,648 ..

2,147,483,6472,147,483,647

shortshort 2 bytes2 bytes --32768 .. 3276732768 .. 32767longlong 8 bytes8 bytes ApproxApprox 9x109x10

1818

bytebyte 1 byte1 byte --128 .. 127128 .. 127

floatfloat 4 bytes4 bytes ApproxApprox 3.4x103.4x10

3838

doubledouble 8 bytes8 bytes ApproxApprox 1.8x101.8x10308308

charchar 2 bytes (Unicode)2 bytes (Unicode)

booleanboolean false, truefalse, true


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The char datatype char represented by a 2char represented by a 2--byte Unicode valuebyte Unicode value

Designed to represent all characters in the writtenDesigned to represent all characters in the written

worldworld Allows 65536 characters (35000 are in use)Allows 65536 characters (35000 are in use)

whereas ascii only allows 255whereas ascii only allows 255

Expressed as hexidecimal Expressed as hexidecimal \\u0000 to u0000 to \\uFFFFuFFFF

((\\u0000 to u0000 to \\u00FF is the ascii set)u00FF is the ascii set) \\u indicates a Unicode valueu indicates a Unicode value

Check outCheck out www.unicode.orgwww.unicode.org for more detailsfor more details


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Variables

Variables must be declared before useVariables must be declared before use

Variable names must begin with a letter butVariable names must begin with a letter but

can contain letters and digitscan contain letters and digits Variable names are case sensitiveVariable names are case sensitive


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Assignment/initialization

Assignment and initialization are identicalAssignment and initialization are identical

to Cto C

int myVariable=20; // initialization

int anotherVariable;

anotherVariable=myVariable; // assignment

char yes=y; // initialization

char cc;

cc=yes; // assignment


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Constant variables

final double electronicCharge=1.6Efinal double electronicCharge=1.6E--19;19;

electronicCharge=1.6EelectronicCharge=1.6E--18;18; // illegal assignment!// illegal assignment!

In Java, the keywordIn Java, the keywordfinalfinaldenotes adenotes a

constantconstant

Constant variables cannot be assigned toConstant variables cannot be assigned to


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Operators

Usual arithmetic operators +Usual arithmetic operators + -- * / are used* / are used

in Java as in Cin Java as in C

Integer divide / and modulus % as in CInteger divide / and modulus % as in C Increment ++ and decrementIncrement ++ and decrement ----

Exponentiation usesExponentiation uses pow()pow() function whichfunction which

is part of theis part of theMathMath classclassdouble y=Math.pow(x,a); // y=xdouble y=Math.pow(x,a); // y=x

aa


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Relational and boolean operators

Java uses the same relational operators as CJava uses the same relational operators as C

== (equal to)== (equal to)

!= (not equal to)!= (not equal to)

, = (less, greater, less or equal, greater or equal), = (less, greater, less or equal, greater or equal)

Java uses the same bitwise operators as CJava uses the same bitwise operators as C

& (and)& (and)

| (or)| (or)

^ (xor)^ (xor)

~ (not)~ (not)


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Boolean expressions

In Java the result of a boolean expression is aIn Java the result of a boolean expression is abooleanboolean type (true or false)type (true or false)

This cant be converted to an int (as in C)This cant be converted to an int (as in C)

if (x == y) {} // Result is a boolean

Java eliminates a commonC programming bugJava eliminates a commonC programming bug

if (x = y) {} // Ok in C, wont compile in

// Java


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Control flow

Java uses the same control structures as in CJava uses the same control structures as in C

Selection (conditional) statementsSelection (conditional) statements

if (..) {}if (..) {}

if (..) {} else if (..) {} . else {}if (..) {} else if (..) {} . else {} switch (..) { case 1: break; default: break; }switch (..) { case 1: break; default: break; }

Iteration statementsIteration statements

for (..) {}for (..) {}

while (..) {}while (..) {} do {} while (..);do {} while (..);


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Example a square root calculator

public class SquareRoot{

public static void main(String[] args){

double a,root;do{

a=Console.readDouble("Enter a positive number : ");if (a


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Computes the square root of an inputtedComputes the square root of an inputted

number using a simple algorithmnumber using a simple algorithm Same control structure as in CSame control structure as in C

Note the use of indentation to indicateNote the use of indentation to indicate

controlcontrol In Java, keyboard input is notIn Java, keyboard input is not

straightforwardstraightforward

Done by theDone by the readDoublereadDouble()() method inmethod in

classclass ConsoleConsole


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Strings

Strings are sequences of characters as in CStrings are sequences of characters as in C

The standard Java library has a predefinedThe standard Java library has a predefinedclassclass StringString

Strings areStrings are immutableimmutable (unlike in C)(unlike in C)

individual characters in the string cannot beindividual characters in the string cannot bechangedchanged

String name = Mike;

name[0] = m; // Not allowed!


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Strings can be concatenated using the +Strings can be concatenated using the +

operatoroperator

In Java, every object, even literals, can beIn Java, every object, even literals, can be

automatically converted to a stringautomatically converted to a string

String name1 = Mike;

String name2 = Spann;

String myName=name1+name2;

String postcode = B+15+ +2+TT;


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TheThe println(.)println(.) function makes use of stringfunction makes use of string

concatentationconcatentation

This works with any data typeThis works with any data type

int age = 25;

System.out.println(I am + age + years old!);

final double pi = 3.14159;

System.out.println(The value of PI = + pi);


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Other string facilities

AAsubstring(.)substring(.) method is provided to accessmethod is provided to access

a substring of a larger stringa substring of a larger string

AA charAt(int n)charAt(int n) method returns themethod returns the

character at positioncharacter at position nn in the stringin the string

String java=Java;String s = java.substring(0,3); // Jav

String java=Java;

char c= java.charAt(2) // v


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AnAn equals(.)equals(.) method tests for string equalitymethod tests for string equality

The == operator should not be usedThe == operator should not be used it testsit tests

to see if the strings are stored in the sameto see if the strings are stored in the samelocation!location!

intintlength()length() returns the length of the stringreturns the length of the string

There are more than 50 methods in the JavaThere are more than 50 methods in the JavaString class! (String class! (java.lang.Stringjava.lang.String))

if (s.equals(Hello)){}


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Arrays

Arrays created with theArrays created with the newnew operatoroperator

Arrays can be created and initialized as in CArrays can be created and initialized as in C

The array length can be determined usingThe array length can be determined usingname.lengthname.length

int[] intArray = new int[20]; // 20 int array

int[] evenNumbers = {2,4,6,8};

for (int j=0; j


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Array variable is effectively a pointer to anArray variable is effectively a pointer to an

array allocated on the heap (hence arraysarray allocated on the heap (hence arrayspassed by reference)passed by reference)

BUTBUT

Cant do pointer arithmetic (as in C)Cant do pointer arithmetic (as in C)

int[] intArray = new int[20]; // creates a 20 int array

intArray++; // NOTALLOWED!


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MultiMulti--dimensional arrays are defined asdimensional arrays are defined as

follows :follows :

Its effectively a 1D array of pointers :Its effectively a 1D array of pointers :

int[] a = new int[5][4]; // 5 x 4 int array

a[][]

a[3]

a[0]

a[1]

a[2]

a[4]

a[3][0]

a[3][1]

a[3][2]

a[3][3]


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Copying arrays

Copying 1 array variable to another isCopying 1 array variable to another is

equivalent (in C) to copying pointersequivalent (in C) to copying pointers

int[] newArray = evenNumbers;

evenNumbers

newArray

22

44

66

88


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The methodThe method System.arraycopy()System.arraycopy() shouldshould

be used to copy the array contentsbe used to copy the array contents System.arraycopy(from, fromIndex, to,System.arraycopy(from, fromIndex, to,

toIndex,n)toIndex,n)

int[] newArray = {0,0,0,0}

System.arraycopy(evenNumbers,0,newArray,0, 4);

evenNumbers

newArray

22

4466

88

22

4466

88


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ClassClass java.utiljava.util..ArraysArrays has a number ofhas a number of

convenience utility functions for arraysconvenience utility functions for arraysArrays.sort(a)Arrays.sort(a) -- sorts arraysorts array aa intointo

ascending orderascending order

Arrays.fill(a,val)Arrays.fill(a,val) fills arrayfills array aa with valuewith value

valval

Arrays.binarySearch(a, key)Arrays.binarySearch(a, key) searchessearches

for a valuefor a value keykey in arrayin array aa

Arrays.equals(a1,a2)Arrays.equals(a1,a2) test fortest for

equivalence of arraysequivalence of arrays a1a1 andand a2a2


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And finally

Basic Java programming is less error proneBasic Java programming is less error prone

than Cthan C

No pointers to worry aboutNo pointers to worry aboutThere is a genuineThere is a genuine booleanboolean typetype

We have yet to think about object orientedWe have yet to think about object oriented

conceptsconceptsClasses are the subject of the next lectureClasses are the subject of the next lecture


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Introduction to the Java lab

All the Java programming assignments for this semesterAll the Java programming assignments for this semesterare now available on my web siteare now available on my web sitehttp://www.eee.bham.ac.uk/spannm/Courses/ee2e.htmhttp://www.eee.bham.ac.uk/spannm/Courses/ee2e.htm

Lab structureLab structure

SemesterSemester 11

LabLab introintro.. ((11 week),week), nonnon--assessedassessed

ClassesClasses ((22 weeks),weeks), assessedassessed

InheritanceInheritance ((22 weeks),weeks), assessedassessed

SwingSwing andand GUIsGUIs ((22 weeks),weeks), assessedassessed

SemesterSemester 22

MajorMajor programmingprogramming assignment,assignment, assessedassessed


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Organisation of the labOrganisation of the lab

You will work in pairsYou will work in pairs

The programming assignments coverThe programming assignments cover

material already done in lecturesmaterial already done in lectures

Please carry out the preparatory workPlease carry out the preparatory work

before the lab with your partnerbefore the lab with your partner

You will need to put in some time outsideYou will need to put in some time outside

the lab slots to finish each exercisethe lab slots to finish each exercise


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Assessment :Assessment :

Makes up 85% of the 2E1 markMakes up 85% of the 2E1 mark There will be 3 programming assignments thisThere will be 3 programming assignments this

semestersemester

Assessed by submission of code + programAssessed by submission of code + program

outputs per lab groupoutputs per lab group

More details will follow and submission willMore details will follow and submission will

be at the end of the semesterbe at the end of the semester

There will be 1 major programming assignmentThere will be 1 major programming assignmentnext semesternext semester

Assessed by a formal lab report per labAssessed by a formal lab report per lab

groupgroup

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