CPSC150 JavaLynn Lambert CPSC150 Spring 2005 Dr. Lambert.

Java Lynn Lambert CPSC150

CPSC150CPSC150

Spring 2005Spring 2005

Dr. LambertDr. Lambert


SyllabusSyllabus

JavaJava CPSC150LabCPSC150Lab No attendance, but Class Assignments No attendance, but Class Assignments

may/may not be put on web; short may/may not be put on web; short turnaroundturnaround

Come see me/Java expert early and oftenCome see me/Java expert early and often Ask questionsAsk questions Consult with (possibly non-expert) peers, Consult with (possibly non-expert) peers,

but be careful. >50% of your grade is but be careful. >50% of your grade is exams.exams.


Why programming Why programming languages?languages?

•Computers understand machine language only•Each computer has its own language•All computer languages are in binary (1s and 0s)•No computer understands English, Powerpoint, or Java


A computer program: A computer program: Add X to Y and store in Add X to Y and store in

ZZ

In machine language:In machine language: 01040100 01040100 (already simplified to decimal)(already simplified to decimal)

01050160 01050160 0404050604040506 0206018002060180

HUH!?HUH!?


AssemblyAssembly

Each machine instruction has matching, Each machine instruction has matching, more English-like assembler:more English-like assembler:

Load X (was: 01040100)Load X (was: 01040100) Load Y (was: 01050160) Load Y (was: 01050160) Add X Y Z (was: 04040506)Add X Y Z (was: 04040506) Store Z (was: 02060180)Store Z (was: 02060180)

Better, but … all this for one addition!?Better, but … all this for one addition!?


JavaJava

z=x+y;z=x+y;

Much better!Much better!

BUT, no machines understand BUT, no machines understand source codesource code. Only . Only machine code.machine code.


Virtual MachineVirtual Machine Review:Review:

Computers understand machine language onlyComputers understand machine language only Each computer has its own languageEach computer has its own language No computer understands English, Powerpoint, No computer understands English, Powerpoint,

or Javaor Java

Java developed to be platform independentJava developed to be platform independent Virtual machine built on top of each actual Virtual machine built on top of each actual

machine to make all machines (windows, mac, machine to make all machines (windows, mac, UNIX) look alikeUNIX) look alike

Java compiles to byte-code – not machine code, Java compiles to byte-code – not machine code, but “virtual machine code”but “virtual machine code”


Why Java?Why Java?

Java is a large, complete languageJava is a large, complete language Works well with web applicationsWorks well with web applications GUIs “part” of the languageGUIs “part” of the language Extensive librariesExtensive libraries (You will get C++ also)(You will get C++ also)


Java and BlueJJava and BlueJ We will use BlueJ for program developmentWe will use BlueJ for program development BlueJ runs on the Java virtual machineBlueJ runs on the Java virtual machine BlueJ is IDE – lots of others (e.g., Eclipse)BlueJ is IDE – lots of others (e.g., Eclipse) BlueJ is free and available for Mac, Windows, BlueJ is free and available for Mac, Windows,

UNIXUNIX You will test and submit program using UNIXYou will test and submit program using UNIX Use your Hunter Creech AccountUse your Hunter Creech Account Download BlueJ for your home machines for Download BlueJ for your home machines for

development: development: www.bluej.orgwww.bluej.org (download Java first: 1.4.2 is on PCS machines): (download Java first: 1.4.2 is on PCS machines):

http://java.sun.com/j2se/1.4.2/download.htmlhttp://java.sun.com/j2se/1.4.2/download.html (Download (Download SDKSDK, NOT , NOT JREJRE))


Why BlueJWhy BlueJ

Easy to useEasy to use Object-orientedObject-oriented Start programming immediatelyStart programming immediately GUI, not console-basedGUI, not console-based Object visualization using UMLObject visualization using UML Debugger, Editor, other standard stuffDebugger, Editor, other standard stuff Simple, not for advanced applicationsSimple, not for advanced applications


•Demo VNC

•BlueJ

•Shapes – compile

• Terms:

•Object, class, method, source code, parameter

• cp /usr/local/examples/shapes .


Week 2Week 2

Writing Java CodeWriting Java Code


ReviewReview

External ViewExternal View In BlueJ main window, In BlueJ main window,

ClassesClasses Object benchObject bench Class relationships Class relationships Create ObjectsCreate Objects Call/Invoke Methods of objectsCall/Invoke Methods of objects


Source Code (Internal Source Code (Internal View)View)

importimport Comments Comments // single line// single line

/* */ multiline/* */ multiline/** */ Javadoc/** */ Javadoc

Class definitionsClass definitionspublic class Picturepublic class Picture{{// fields// fields// constructors// constructors// methods// methods}}


Class details: Class details: fields/attributesfields/attributes

Lifetime/scope of classLifetime/scope of class private int myfield; // primitiveprivate int myfield; // primitive

char, boolean, double, a few otherschar, boolean, double, a few others private String mystring; // classprivate String mystring; // class private Circle sun;private Circle sun;

user and library defineduser and library defined BlueJ: primitive has data; object has BlueJ: primitive has data; object has

pointerpointer Clock example, ClockDisplay, NumberDisplayClock example, ClockDisplay, NumberDisplay


Class details: Class details: constructorsconstructors

Initialize objects. Called when object is createdInitialize objects. Called when object is created no return typeno return type can be overloadedcan be overloaded

public Circle()public Circle() {{

diameter = 30;diameter = 30;xPosition = 20;xPosition = 20;yPosition = 60;yPosition = 60;color = "blue";color = "blue";isVisible = false;isVisible = false;

}}

public Circle(int d, int x, int y, color public Circle(int d, int x, int y, color c)c) {{

diameter = d;diameter = d;xPosition = x;xPosition = x;yPosition = y;yPosition = y;color = c;color = c;isVisible = false;isVisible = false;

}}


Class Details: MethodsClass Details: Methods

General Structure:General Structure:public/private return-type name public/private return-type name

(param1name param1type, param2name (param1name param1type, param2name param2type)param2type)

changeColor method from Circle:changeColor method from Circle: public void changeColor(String newColor)public void changeColor(String newColor) {{

color = newColor;color = newColor;draw();draw();

}}

return type void

first line signature or header

method call (internal to class)

Java statements inside body, e.g., single = assignment

curly braces, stuff inside is method body

formal parameter


Method vs. FieldMethod vs. Field

Both have private or publicBoth have private or public Both have typesBoth have types Both have namesBoth have names fields have ‘;’ at end of line/methods do notfields have ‘;’ at end of line/methods do not methods have () (even without methods have () (even without

parameters); fields do notparameters); fields do not methods have a body; fields do notmethods have a body; fields do not fields have memory to hold information; fields have memory to hold information;

methods do notmethods do not


Field vs. Local variableField vs. Local variable

local variables declare in a method; local variables declare in a method; fields outside of all methodsfields outside of all methods

local variables have the lifetime of local variables have the lifetime of the method callthe method call

local variables and fields have type local variables and fields have type and ‘;’and ‘;’

local variables do NOT have local variables do NOT have private/public designationprivate/public designation


Writing methods:Writing methods:More Java statementsMore Java statements

Arithmetic ExpressionsArithmetic Expressions Compound AssignmentCompound Assignment System.out.printlnSystem.out.println thisthis newnew dot notationdot notation returnreturn


ArithmeticArithmetic

+, /, *, -, %+, /, *, -, % Codepad (Choose view, then Codepad (Choose view, then

codepad)codepad) Be careful about integer divisionBe careful about integer division 4/3 4/3 rr 3 3


Compound AssignmentCompound Assignment assignment:assignment:

answer = factor1 * factor2;answer = factor1 * factor2; answer = answer + newsum;answer = answer + newsum;

compound assignmentcompound assignment answer += newsum;answer += newsum; answer -= diff;answer -= diff; answer *= product; // e.g., factorialanswer *= product; // e.g., factorial answer /= digit; // getting rid of digitsanswer /= digit; // getting rid of digits answer %= digit; answer %= digit;

Use codepadUse codepad int answer=30; answer %= 4; int answer=30; answer %= 4;

System.out.println("Answer is " + answer);System.out.println("Answer is " + answer);


System.out.println()System.out.println()

To print out messages to a terminalTo print out messages to a terminal Can print strings or integersCan print strings or integers Use + to concatenate/append. Be Use + to concatenate/append. Be

careful with numberscareful with numbers e.g.,e.g.,

System.out.println("Answer is " + answer); System.out.println("Answer is " + answer); System.out.println(answer + answer);System.out.println(answer + answer); System.out.println(“answer is” + answer + System.out.println(“answer is” + answer +

answer);answer);


thisthis

public void public void

changeColor(String newColor)changeColor(String newColor)

{{

color = newColor;color = newColor;

draw();draw();

}}

public void public void changeColor(String color)changeColor(String color) {{

this.color = color;this.color = color;draw();draw();

}}

this specifies the current object


new, dot notationnew, dot notation

public void draw()public void draw()

{{

wall = new Square();wall = new Square();

wall.moveVertical(80);wall.moveVertical(80);

wall.changeSize(100);wall.changeSize(100);

wall.makeVisible();wall.makeVisible();//rest of method from Picture class//rest of method from Picture class

}}

To create a new object, use new. calls

constructor

Extermal method calldot notation


return statementreturn statement

public int sum(int x, int y)public int sum(int x, int y)

{{

int answer;int answer;

answer = x+y;answer = x+y;

return answer;return answer;

}}

type of method is return type

to return a value, use ‘return value’; can be

calculation


Common Methods to Common Methods to WriteWrite

Wizard at writing code; let’s look at Wizard at writing code; let’s look at common methodscommon methods

Mutator method: change value of a Mutator method: change value of a fieldfield e.g., setTime in Clocke.g., setTime in Clock

Accessor method: get the value of a Accessor method: get the value of a fieldfield e.g., getTime in Clocke.g., getTime in Clock


Common methods: Common methods: AccessorAccessor

Retrieve the value of a fieldRetrieve the value of a field no parameter, return type is type of fieldno parameter, return type is type of field method body is one linemethod body is one linepublic class fractionpublic class fraction{ // only a little bit defined{ // only a little bit defined private int numerator;private int numerator; private int denominator;private int denominator;

public int GetNum()public int GetNum(){{return numerator;return numerator;}}}}


Common Method: Common Method: mutatormutator

Changes field valueChanges field value void return type, one parameter is new valuevoid return type, one parameter is new value not all fields have to have mutator methodsnot all fields have to have mutator methodspublic class fractionpublic class fraction{// only a portion of this class{// only a portion of this class private int numerator;private int numerator; private int denominator;private int denominator;

public void SetNum(int newvalue)public void SetNum(int newvalue){{numerator = newvalue;numerator = newvalue;}}}}


ConditionalsConditionals Execute code under some conditionsExecute code under some conditions In CanvasIn Canvaspublic static Canvas getCanvas()public static Canvas getCanvas()

{ // only create Canvas if not already created{ // only create Canvas if not already created if (canvasSingleton == null) {if (canvasSingleton == null) {

canvasSingleton = new Canvas("BlueJ Shapes Demo", canvasSingleton = new Canvas("BlueJ Shapes Demo", 300, 300, 300, 300,

Color.white);Color.white);

}} canvasSingleton.setVisible(true);canvasSingleton.setVisible(true); return canvasSingleton;return canvasSingleton;}}


if statementsif statements

if (booleanexpression)if (booleanexpression)

java statement;java statement;

any Java statement you know about

we don’t know about this


Boolean ExpressionsBoolean Expressions

Evaluate to be true or falseEvaluate to be true or false boolean variablesboolean variables

boolean isVisible = false;boolean isVisible = false; relational expressions (compares relational expressions (compares

values)values) logical expressions (compares logical expressions (compares

expressions with and, or, not)expressions with and, or, not)


Relational OperatorsRelational Operatorsfor primitivesfor primitives

int x, y;int x, y; x < yx < y x <= yx <= y x > yx > y x >= yx >= y x != yx != y x == y // NOT x=yx == y // NOT x=y

NOTE: most of these don’t work for NOTE: most of these don’t work for classes (== is a problem)classes (== is a problem)


Evaluating Boolean Evaluating Boolean ExpressionsExpressions

int x=3; int y = 4; int z=5;int x=3; int y = 4; int z=5;

x < yx < y

x < y < zx < y < z

x = yx = y

y == 4y == 4

z >= xz >= x

x != 3x != 3

(x + 4) < (y - 1)(x + 4) < (y - 1)

truetrue

error: error: < cannot be applied to boolean,int< cannot be applied to boolean,int

error: incompatible types - found int; expected boolean error: incompatible types - found int; expected boolean

truetrue

falsefalse

falsefalse

7 < 3; false7 < 3; false


Logical OperatorsLogical Operators and (&&, single & very different)and (&&, single & very different)

both values must be true for the expression to be both values must be true for the expression to be truetrue

if it is cold and rainy, wear your winter raincoat if it is cold and rainy, wear your winter raincoat (both must be true)(both must be true)

or (|| - on keyboard, called pipe symbol)or (|| - on keyboard, called pipe symbol) either value can be trueeither value can be true if it is cold or rainy, wear a coat (if either or both is if it is cold or rainy, wear a coat (if either or both is

true, do)true, do) not (!)not (!)

changes the truth value of the expressionchanges the truth value of the expression if it is not cold, do not wear a winter coatif it is not cold, do not wear a winter coat


Logical OperatorsLogical Operators

int x=3; int y=10;int x=3; int y=10;

(x < y) && (y < 20)(x < y) && (y < 20)

(x == 3) || (y == 3)(x == 3) || (y == 3)

x < y; 3 < 10; truex < y; 3 < 10; true

y < 20; 10 < 20; truey < 20; 10 < 20; true

true && true is truetrue && true is true

x == 3 true.x == 3 true.

short circuit short circuit evaluationevaluation

(y==3 false(y==3 false

true || false is true)true || false is true)


More logical operatorsMore logical operators

int x=3; int y=10;int x=3; int y=10;

!(y=10)!(y=10)

(x != 3) || (y != 3)(x != 3) || (y != 3)

trick questiontrick question

errorerror

!(y==10)!(y==10)

y == 10 truey == 10 true

!true false!true false

x != 3 falsex != 3 false

Keep going. y != 3 Keep going. y != 3 truetrue

false || true is truefalse || true is true


Yet more logical Yet more logical operatorsoperators

int x=3; int y=10;int x=3; int y=10;!((x+1 < 4) ||!((x+1 < 4) ||

(y <= 10))(y <= 10))

!((x+1 < 4) &&!((x+1 < 4) &&

(y <= 10))(y <= 10))

x+1 = 4x+1 = 44 < 4 false.keep 4 < 4 false.keep

goinggoingy <= 10 truey <= 10 truefalse || true truefalse || true true! true is false! true is false4 < 4 false. DONE 4 < 4 false. DONE

with &&. Do not with &&. Do not look at y <=10.look at y <=10.

!false true!false true


Strings and ClassesStrings and Classes

== tests if objects are equal (point == tests if objects are equal (point to the same thing), NOT if they have to the same thing), NOT if they have the same content. May return false the same content. May return false when true should be returnedwhen true should be returned

use equalsuse equals no corresponding <, lessthan,…no corresponding <, lessthan,… use compareTouse compareTo


CompareToCompareTo

Returns 0 if 2 Strings are equalReturns 0 if 2 Strings are equal Returns negative number if Returns negative number if

object<parameterobject<parameter Returns positive number if object > Returns positive number if object >

parameterparameter


compareTo codecompareTo code

String s1 = “Here is a string”;String s1 = “Here is a string”;String s2 =“Here is another string”;String s2 =“Here is another string”;String s3 = “here is another string”;String s3 = “here is another string”;if (s1.compareTo(s2) < 0)if (s1.compareTo(s2) < 0) System.out.println(“s1 less than s2”); System.out.println(“s1 less than s2”); if (s2.compareTo(s1) < 0)if (s2.compareTo(s1) < 0) System.out.println(“s2 less than s1”); System.out.println(“s2 less than s1”); if (s2.compareTo(s3) < 0) // case matters; uppercase if (s2.compareTo(s3) < 0) // case matters; uppercase

< lowercase< lowercase System.out.println(“s2 less than s3”); System.out.println(“s2 less than s3”); if (s3.compareTo(s2) < 0)if (s3.compareTo(s2) < 0) System.out.println(“s3 less than s2”); System.out.println(“s3 less than s2”);

// will print// will print

// will not print// will not print




More String More String comparisionscomparisions

String s1 = “Here is a string”;String s1 = “Here is a string”;String s2 =“Here is a string”;String s2 =“Here is a string”;String s3 = “here is another string”;String s3 = “here is another string”;if (s1.compareTo(s2) == 0)if (s1.compareTo(s2) == 0) System.out.println(“s1 is the same as s2”);System.out.println(“s1 is the same as s2”);if (s2.compareTo(s1) == 0)if (s2.compareTo(s1) == 0) System.out.println(“s2 still the same as s1”);System.out.println(“s2 still the same as s1”);if (s2.equals(s1))if (s2.equals(s1)) System.out.println(“s2 is STILL the same as s1”);System.out.println(“s2 is STILL the same as s1”);if (s3.compareTo(s2) == 0) if (s3.compareTo(s2) == 0) System.out.println(“s3 is the same as s2”);System.out.println(“s3 is the same as s2”);if (s1 == s2)if (s1 == s2) System.out.println(“s1 and s2 point to the same System.out.println(“s1 and s2 point to the same

object”);object”);// will not print// will not print

// will print; symmetric// will print; symmetric




// compareTo == 0 is same as equals// compareTo == 0 is same as equals


if statementsif statements if statement form:if statement form:

if (boolean expression) if (boolean expression)

java statement;java statement;

if (x < y)if (x < y)

System.out.println(“x < y”);System.out.println(“x < y”);

you know both parts

now


if statements cautionsif statements cautions MUST have ()s around boolean expressionMUST have ()s around boolean expression no syntax error for non-boolean like no syntax error for non-boolean like

expressionsexpressions only ONE statement in an if statementonly ONE statement in an if statement no ';' after if conditionno ';' after if condition Make sure you account for values that are Make sure you account for values that are

equalequal use relational operators only with use relational operators only with

primitivesprimitives use equals, compareTo with Stringuse equals, compareTo with String


if-elseif-else

If you want to do one thing if a condition is If you want to do one thing if a condition is true and something else if not, use if-else.true and something else if not, use if-else. form: if (condition)form: if (condition)

Java statementJava statement elseelse Java statementJava statement

if (x < y)if (x < y) System.out.println(x + " is less than the other System.out.println(x + " is less than the other

number”);number”);elseelse System.out.println(y + " is less than the other System.out.println(y + " is less than the other

number”);number”);


> one statement in an if> one statement in an ifIf you want to have more than one statement If you want to have more than one statement

inside an if or an else, use {}s:inside an if or an else, use {}s:if (x < y) if (x < y)

{{

System.out.println(x + " is less than the System.out.println(x + " is less than the other number”);other number”);

x = 0;x = 0;

}}

elseelse

{{

System.out.println(y + " is less than the other System.out.println(y + " is less than the other number”);number”);

y = 0;y = 0;

}}


If-else cautionsIf-else cautions

either if clause or else clause or both either if clause or else clause or both may have {}s.may have {}s.

After statements inside if and else After statements inside if and else clause are executed, control passes clause are executed, control passes back to next sequential statementback to next sequential statement

no ';' after elseno ';' after else Make sure you account for values Make sure you account for values

that are equalthat are equal


Class WorkClass Work Write an if statement to assign x to y if x is Write an if statement to assign x to y if x is

greater than ygreater than y Consider a classConsider a classpublic class MyStringpublic class MyString{ private String s;{ private String s;// write method here// write method here}}Write the method lessThan that takes a String Write the method lessThan that takes a String

as a parameter and returns true if s (from as a parameter and returns true if s (from MyString) is less than its String parameterMyString) is less than its String parameter


Watch OutWatch Out

if (3 < 4)if (3 < 4)

x = 3;x = 3;

elseelse

System.out.println(“3 < 4 is false”);System.out.println(“3 < 4 is false”);

x = 0;x = 0;

System.out.println(System.out.println("the value of x is " + "the value of x is " + x);x);


Embedded ifsEmbedded ifs

If statements and if-else statements If statements and if-else statements may be embedded (if within if). may be embedded (if within if). simply evaluate them as the Java simply evaluate them as the Java code is executed:code is executed:

if-else example is most common. if-else example is most common. sets up a table of conditionssets up a table of conditions


Embedded if-else for Embedded if-else for tabletable

if (ave >= 90)if (ave >= 90) grade = 'A';grade = 'A';else if ((ave < 90) && (ave >= 80))else if ((ave < 90) && (ave >= 80)) // note: need ()s around entire condition// note: need ()s around entire condition grade = 'B'; grade = 'B'; else if ((ave < 80) && (ave >=70))else if ((ave < 80) && (ave >=70)) grade = 'C';grade = 'C';else if ((ave < 70) && (ave >=60))else if ((ave < 70) && (ave >=60)) grade = 'D';grade = 'D';else if ((ave < 70) && (ave < 60))else if ((ave < 70) && (ave < 60)) grade = 'F';grade = 'F';


Tracing through the Tracing through the embedded ifembedded if


Fixing the embedded ifFixing the embedded ifif (ave >= 90)if (ave >= 90) grade = 'A';grade = 'A';else if (ave >= 80)else if (ave >= 80)// We know (ave < 90) or we wouldn't be // We know (ave < 90) or we wouldn't be

herehere grade = 'B'; grade = 'B'; else if (ave >=70) // we know ave < 80else if (ave >=70) // we know ave < 80 grade = 'C';grade = 'C';else if (ave >=60)else if (ave >=60) grade = 'D';grade = 'D';else else // if ((ave < 70) && (ave < 60))// if ((ave < 70) && (ave < 60)) grade = 'F';grade = 'F';


Cautions for embedded Cautions for embedded ifsifs

Don't use redundant comparisonsDon't use redundant comparisons Make sure you check for values that Make sure you check for values that

are equalare equal Account for out of range valuesAccount for out of range values


Program styleProgram style

Put {}s on a line by themselvesPut {}s on a line by themselves indent {}s 2-3 spaces, statements indent {}s 2-3 spaces, statements

one more than thatone more than that All code outside if statements should All code outside if statements should

line upline up All code inside of if statements All code inside of if statements

should line up.should line up.


More complicated More complicated embedded ifsembedded ifs

if (x < 3)if (x < 3) if (y < 6)if (y < 6) System.out.println( "x and y between 3 System.out.println( "x and y between 3

and 6");and 6"); elseelse System.out.println( "x < 3; y >= 6");System.out.println( "x < 3; y >= 6");elseelse if (y > 6)if (y > 6) System.out.println( "x and y not in 3-6 System.out.println( "x and y not in 3-6

range"); range"); elseelse System.out.println( "x >= 3); y <= 6 ");System.out.println( "x >= 3); y <= 6 ");


Arrays and LoopsArrays and Loopsweek 4week 4

Chapter 4Chapter 4


Each variable only holds one itemEach variable only holds one item if > 1 item wanted, need an arrayif > 1 item wanted, need an array array that holds a wordarray that holds a word arrays hold elements all of the same arrays hold elements all of the same

typetype

char[ ] word = new char[4];char[ ] word = new char[4]; holds 4 elements of type charholds 4 elements of type char

ArraysArrays

0 1 32

word


char[ ] word = new char[4];

two parts to an array:

index -- integer

element – type inside array

'h' 'e'

0 1 32

'h'

0 1 32

word[1] = 'e';

'h' 'e' 'o''r'

0 1 32

'h' 'e' 'o'

0 1 32

word[3] = 'o';

word[2] = 'r';

word[0] = 'h';


Can use variables for index OR elementsCan use variables for index OR elementsint i=3; char new = 'd';int i=3; char new = 'd';word[i] = new;word[i] = new;

can find lengthcan find lengthword.length // is 4word.length // is 4 largest index is always length – 1largest index is always length – 1 word[4] is RUN time errorword[4] is RUN time error

Array manipulationArray manipulation

'h' 'e' 'o''r'

0 1 32

'h' 'e' 'd''r'

0 1 32


arrays and newarrays and new

char[ ] word;char[ ] word; creates word that is of type char creates word that is of type char

array that points to nothingarray that points to nothing

word = new word[4];word = new word[4]; creates array of 4 elements creates array of 4 elements

initialized to \u0000 (Java always initialized to \u0000 (Java always initializes primitives to 0)initializes primitives to 0)


Myarray exampleMyarray example

public class Myarraypublic class Myarray

{{

private static private static Circle[] circles;Circle[] circles;

private static private static double[] area; double[] area;

// other stuff in the // other stuff in the classclass

} }


Myarray gets elements Myarray gets elements allocatedallocated

Create an object Create an object

circles = new circles = new Circle[4];Circle[4];

area = new area = new double[4];double[4];


createcircles()createcircles()

createcircles()createcircles()

circles[0] = new circles[0] = new Circle(); Circle();


array creation summaryarray creation summary char[ ] word;char[ ] word;creates a space named word that contains nullcreates a space named word that contains null word = new char [4];word = new char [4];allocates 4 chars, initialized, word points to allocates 4 chars, initialized, word points to

themthem classes: Circle[ ] mycircles;classes: Circle[ ] mycircles;same as word same as word mycircles = new Circle[4];mycircles = new Circle[4];allocates 4 spaces that contain nullallocates 4 spaces that contain null mycircles[0] = new Circle( );mycircles[0] = new Circle( );creates an actual circlecreates an actual circle


Repetition in arraysRepetition in arrays

arrays often do the same thingarrays often do the same thing

(e.g., for each Circle in array, create a (e.g., for each Circle in array, create a Circle)Circle)

for (int i=0; i<circles.length; i++)for (int i=0; i<circles.length; i++)

circles[i] = new Circle( );circles[i] = new Circle( );

memorize this line


Do: In a groupDo: In a group

Write code to declare a 4 character word Write code to declare a 4 character word array, then write a loop to initialize chars in array, then write a loop to initialize chars in word to be 'A' word to be 'A'

Write code to declare a 4 character array, then Write code to declare a 4 character array, then write a loop to initalize chars in word to be write a loop to initalize chars in word to be ABCD (do this in a loop). Hint: use a separate ABCD (do this in a loop). Hint: use a separate variable for the element value (start with 'A')variable for the element value (start with 'A')

Declare an int array with 10 integers and Declare an int array with 10 integers and write a loop to put the value of the index into write a loop to put the value of the index into the element (e.g., intarray[3] should have the the element (e.g., intarray[3] should have the value 3)value 3)


““while” and “for” while” and “for” StructuresStructuresDr. Roberto A. FloresDr. Roberto A. Flores

CPSC 150 – Computers and Programming I


• It repeats a set of statements while a condition is true.

while ( condition ) { is TRUE execute these statements;}

““while” structureswhile” structures


““while” structureswhile” structures• It repeats a set of statements while a condition is true.

while ( condition ) { is TRUE execute these statements;}

22

11

33The dynamics of “while”

Evaluate condition: • if TRUE go to 2• If FALSE go to 3

Execute statements, and then go to 1Continue with next statement.

The dynamics of “while”Evaluate condition:

• if TRUE go to 2• If FALSE go to 3

Execute statements, and then go to 1Continue with next statement.

1.

2.3.



int speedLimit = 55;int speed = 0;

while ( speed < speedLimit ) { speed = speed + 1;}// since we don’t want a ticket…speed = speed - 1;

• What is the value of “speed” at this point?



int speedLimit = 55;int speed = 0;

while ( speed < speedLimit ) { speed = speed + 1;}// since we don’t want a ticket…speed = speed - 1;

initialize variablesin conditional

initialize variablesin conditional

1

modify variablesin conditional

modify variablesin conditional

2


““while” structureswhile” structures• Adding the values of an array of integers

int grades[] = new int[1000];/* the values of the elements are somehow initialized here.*/int i = 0;int sum = 0;

while ( i < grades.length ) { sum += grades[i]; i++;}

System.out.println(“The sum is ” + sum);


““while” structures: while” structures: ExercisesExercises

• Determine the output of the following methods:

public void foo1() { int i=0; while (i <= 20) { System.out.println( i ); i = i + 4; } }

public void foo2() { int i = 20; while (i > 0) { i = i / 2; System.out.println( i ); }}



1. Write a method named “countDown” that receives an integer parameter named “number”, and displays (using System.out.println) all numbers from the number down to 0.• For example, if the parameter was 8, the method should

display numbers 7, 6, 5, 4, 3, 2, 1, 0, in this order and with each number in one line.

2. Write a method named “countEven” that receives an integer parameter named “number”, displays (using System.out.println) all even numbers between 0 and the number received, and returns a integer value with the number of even numbers displayed.• For example, if the parameter was 8, the method should

display numbers 2, 4 and 6, in this order and with each number in one line, and return a value of 3 (which is how many even numbers were between 0 and 8).



3. Write a method named “reverse” that receives an integer parameter named “number” and displays (using System.out.println) the number with all digits reversed. The method should only work with positive parameter values.• For example, if the number was 2001, the method

should display 1002. (Hint: use modulus by 10 to extract the last digit from the number, and then divide the number by 10 before extracting the next digit).


““for” structuresfor” structures• It (also) repeats statements while a condition is true.

initialstatement

loopcondition

modifystatement

2211 44

33

55The dynamics of “for”

1. Initialize condition variables.2. Evaluate loop condition:


3. Execute statements; then go to 44. Modify condition variables; then go to 25. Continue with next statements.

The dynamics of “for”1. Initialize condition variables.2. Evaluate loop condition:


3. Execute statements; then go to 44. Modify condition variables; then go to 25. Continue with next statements.

for ( ; ; ){ statements;}


Revisiting “while” Revisiting “while” exercise with “for”exercise with “for”

• Write a method named “countEven” that receives an integer parameter named “number”, displays (using System.out.println) all even numbers between 0 and the number received, and returns a integer value with the number of even numbers displayed.

public int countEven(int number) { int count = 0, i = 2; while (i < number) { if (i % 2 == 0) { System.out.println( i ); count++; } i++; } return count;}


““for” structures: for” structures: ExercisesExercises

1. Write a method named “factorial” that calculates the factorial of an integer parameter named “number” (where factorial is the multiplication of all numbers from 1 to number-1). The method should return an integer number with the result of the factorial, and it should work only with positive numbers (return 0 in the case of non-positive parameter numbers).

2. Write a method named “prime” that returns a boolean value indicating whether an integer parameter named “number” is a prime number (where a prime number is a number that is not divisible without remainder by any other numbers except 1 and the number itself). The method should work only with positive numbers (return false if a negative parameter number is given).Sample list of prime numbers: 2, 3, 5, 7, 11, 13, 19, 23…


““for” structures: for” structures: ExercisesExercises

3. Write a method named “digits” that displays (using System.out.println) the digits of an integer parameter named “number” separated by dashes (“-”). For example, when receiving the number 1234 as a parameter, the method should display “1-2-3-4”.

• Hints: use an array to store each digit as you extract them using the modulus operator. Since these digits are stored in the array in the inverse order as they are found in the number, you will need to print them backwards. Also, note that the last digit does not have a trailing dash!


ContainersContainers(ArrayList)(ArrayList)

Chapter 4Chapter 4


ArrayListArrayList Like arrays, but have built in operatorsLike arrays, but have built in operators Use library (package)Use library (package)

import java.util.ArrayList;import java.util.ArrayList; Declare variableDeclare variable

private ArrayList circles;private ArrayList circles; To create a listTo create a list

circles = new ArrayList( ); // not NOT circles = new ArrayList( ); // not NOT CircleCircle

To add an element to the list (like To add an element to the list (like Circle c)Circle c)circles.add(c)circles.add(c)


More ArrayList methodsMore ArrayList methods

To find the size:To find the size:circles.size();circles.size();

To retrieve an element:To retrieve an element:circles.get(1); //circles.get(1); // returns the second returns the second elementelement

To remove an elementTo remove an elementcircles.remove(1); circles.remove(1); // removes the second // removes the second elementelement


ArrayList loopArrayList loop for loop with indexfor loop with indexfor (int i=0;i<circles.size( ); i++)for (int i=0;i<circles.size( ); i++) circles.get(i); // this returns the ith circlecircles.get(i); // this returns the ith circle iteratorsiteratorsimport java.util.Iterator;import java.util.Iterator;for (Iterator it = circles.iterator(); for (Iterator it = circles.iterator();

it.hasNext( ); it.next( ))it.hasNext( ); it.next( )) ; ;

Remember the ()s unlike arrays

increment part of body


Chapter 6Chapter 6

TestingTesting


Testing/DebuggingTesting/Debugging

Syntax errors: Initially fixing syntax Syntax errors: Initially fixing syntax errors the hard part. After that, errors the hard part. After that, fixing logic errors:fixing logic errors:

Testing: Ensuring that your code Testing: Ensuring that your code works works

Debugging: finding where code is Debugging: finding where code is incorrectincorrect


Levels of TestingLevels of Testing

Unit testingUnit testing Application testingApplication testing

Always start at the lowest levelAlways start at the lowest level Test after every method is writtenTest after every method is written Use these tests throughout. after Use these tests throughout. after

each method, run all of the old testseach method, run all of the old tests


The good, the bad, the The good, the bad, the uglyugly

Test cases that will workTest cases that will work Test cases that will not workTest cases that will not work Test cases that should not happenTest cases that should not happen


Types of Testing (in Types of Testing (in BlueJ)BlueJ)

InspectionInspection System.out.printlnSystem.out.println Regression TestingRegression Testing

Create tests and rerun them for each new Create tests and rerun them for each new developmentdevelopment

To do that, Test Harness/Test RigTo do that, Test Harness/Test Rig Class whose sole purpose is to test another Class whose sole purpose is to test another

classclass To do that, Automatic Testing using junitTo do that, Automatic Testing using junit To do that, Record TestsTo do that, Record Tests


ExampleExample

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CPSC150 JavaLynn Lambert CPSC150 Spring 2005 Dr. Lambert.

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