java android programming

8/10/2019 Java Android Programming

http://slidepdf.com/reader/full/java-android-programming 1/71

Tutorial: Programming in Javafor Android Development

Adam C. Champion and Dong Xuan

CSE 4471: Information SecurityAutumn 2013

Based on material from C. Horstmann [1], J. Bloch [2], C. Collins et al. [4],M.L. Sichitiu (NCSU), V. Janjic (Imperial College London), CSE 2221 (OSU), and other sources



Outline

• Getting Started• Java: The Basics• Java: Object–Oriented Programming• Android Programming



Getting Started (1)• Need to install Java Development Kit (JDK) to write

Java (and Android) programs – Do not install Java Runtime Environment (JRE);

JDK and JRE are different!• Can download the JDK for your OS at http://java.oracle.com • Alternatively, for OS X, Linux:

– OS X:• Open !"##$%&'(%)*+!,(%$%(%-+!.-/0%*'$1'## • Type 3'4'& at command line• Install Java when prompt appears

– Linux:• Type +56) '#(78-( %*+('$$ 6-9'5$(736: at command line

(Debian, Ubuntu)• Other distributions: consult distribution’s documentation



Install!



Getting Started (2)• After installing JDK, download Android SDK

from http://developer.android.com • Simplest: download and install Android

Developer Tools (ADT) bundle (includingAndroid SDK) for your OS• Alternatives:

– Download/install Android Studio (beta) from this site(based on IntelliJ IDEA)

– Install Android SDK tools by themselves, then installADT for Eclipse separately (from this site)

• We’ll use ADT with SDK (easiest)



Install!



Getting Started (3)• Unzip ADT package to directory ;'6(7<5*6$-7)+= , then run

;'6(7<5*6$-7)+=!-&$%#+-!>&$%#+- app. You should see this:



Getting Started (4)• Go to Eclipse preferences

(Window ! Preferences or ADT ! Preferences ), selectAndroid tab

• Make sure the Android SDK path is correct ( ;'6(7<5*6$-7)+=!+6: )

• Strongly recommend testing

with real Android device – Android emulator: very slow – Install USB drivers for your

Android device



Getting Started (5)• Bring up the Android SDK Manager

– Recommended: Install Android 2.2, 2.3.3 APIs and 4.x API – Do not worry about Intel x86 Atom, MIPS system images

• In Eclipse, click Window ! Show View ! Other… andselect views Android ! Devices , Android ! LogCat

• Now you’re ready for Android development!



Outline

• Getting Started• Java: The Basics• Java: Object–Oriented Programming• Android Programming



Java Programming Language• Java: general–purpose

language designed sodevelopers write codeonce, it runs anywhere

• The key: Java VirtualMachine (JVM)

– Program code compiled toJVM bytecode

– JVM bytecode interpretedon JVM

• We’ll focus on Java 5(Android uses this). Seechapters 1–7 in [1].



Our First Java Program (1)#5<$%& &$'++ ?-$$)@)/$6A

#5<$%& +('(%& 4)%6 0'%*BC(/%*8DE '/8+FA

CG+(-01)5(1#/%*($*BH?-$$) I)/$6JKFLM

M

• Don’t forget to match curly braces A,M or semicolon at the end!•

In Eclipse: File ! New ! Java Project , name project“?-$$)@)/$6 ” (no quotes), click Finish. Open ?-$$)@)/$6 inPackage Explorer. Right–click +/& directory, select New ! Class ,and create a class ?-$$)@)/$6 with a 0'%*BF method. To run the

program, right–click HelloWorld project, click Run As



Our First Java Program (2)

Right–click, New ! Class



Explaining the Program• Every .java source file contains one class

– We create a class ?-$$)@)/$6 that greets user – The class ?-$$)@)/$6 must have the same name as the source file

?-$$)@)/$613'4' – Our class has #5<$%& scope, so other classes can “see” it – We’ll talk more about classes and objects later

• Every Java program has a method 0'%*BF that executes the program – Method “signature” must be exactly

#5<$%& +('(%& 4)%6 0'%*BC(/%*8DE '/8+F A 111 M – This means: (1) 0'%*BF is “visible” to other methods; (2) there is “only

one” 0'%*BF method in the class; and (3) 0'%*BF has one argument('/8+ , an array of C(/%*8 variables)

– Java “thinks” 0'%*BF, N'%*BF, 0%"OBF are different methods• Every Java method has curly braces A,M surrounding its code• Every statement in Java ends with a semicolon, e.g.,

CG+(-01)5(1#/%*($*BH?-$$) I)/$6JKFL • Program prints “ ?-$$) I)/$6J ” to the console, then quits



Basic Data Types (1)• Java variables are instances of mathematical “types”

– Variables can store (almost) any value their type can have – Example: the value of a boolean variable can be either (/5- or 9'$+-

because any (mathematical) boolean value is true or false – Caveats for integer, floating–point variables: their values are subsets of

values of mathematical integers, real numbers. Cannot assignmathematical 2500 to integer variable (limited range) or mathematical ! 2to a floating–point variable (limited precision; irrational number).

– Variable names must start with lowercase letter, contain only letters,numbers, P

• Variable declaration : <))$-'* < Q (/5-L• Later in the program, we might assign 9'$+- to <: < Q 9'$+-L• Java strongly suggests that variables be initialized at the time of

declaration, e.g., <))$-'* <L gives a compiler warning ( *5$$ pointer)• Constants defined using 9%*'$ keyword, e.g.,

9%*'$ <))$-'* 9'$+-R))$ Q S"TC>L



Basic Data Types (2)• Java’s primitive data types: [5]

Primitive type Size Minimum Maximum Wrapper type

<))$-'* 1–bit N/A N/A R))$-'*&U'/ 16–bit Unicode 0 Unicode 2 16 – 1 VU'/'&(-/

<G(- 8–bit –128 +127 RG(-

+U)/( 16–bit –2 15 +2 15 – 1 CU)/(

%*( 32–bit –2 31 +2 31 – 1 W*(-8-/

$)*8 64–bit –2 63 +2 63 – 1 T)*8

9$)'( 32–bit IEEE 754 IEEE 754 S$)'(

6)5<$- 64–bit IEEE 754 IEEE 754 X)5<$-

Note: All these types are signed, except &U'/ .



Basic Data Types (3)• Sometimes variables need to be cast to another type, e.g.,

if finding average of integers:%*( %*(Y*- Q Z[ %*(.I) Q \[ %*(.U/-- Q ][ *50W*(+ Q \L6)5<$- 6)5<Y*- Q B6)5<$-F%*(Y*-[ 6)5<.I) Q B6)5<$-F0GW*(.I)[ 6)5<.U/-- QB6)5<$-F%*(.U/--L6)5<$- '48 Q B6)5<Y*- ^ 6)5<.I) ^ 6)5<.U/--F!B6)5<$-F*50W*(+L

• N'(U library has math operations like +_/(BF , #)IBF , etc.• C(/%*8 : immutable type for sequence of characters

– Every Java variable can be converted to C(/%*8 via ()C(/%*8BF –

The ^ operation concatenates C(/%*8s with other variables – Let +(/ be a C(/%*8 . We can find +(/ ’s length ( +(/1$-*8(UBF ),

substrings of +(/ (+(/1+5<+(/%*8BF ), and so on [6]



Basic Data Types (4)• A literal is a “fixed” value of a variable type

– .`,> , S"TC> are <))$-'* literals – ‘" ’, ‘a( ’, ‘aK’, and ‘ a5b]&b ’ are &U'/ literals (escaped

tab, quote characters, Unicode value for \pi) – 7Z, b, b]c , bdZ' are %*( literals (last two are octal andhexadecimal)

– b1c , Z1b, Z>e, e1b\]>\] are 6)5<$- literals – “"( YC, ”, “ ?-$$) I)/$6J ” are C(/%*8 literals

• Comments: – Single-line: !! +)0- &)00-*( () -*6 )9 $%*- – Multi-line: !f &)00-*(+ +#'* 05$(%#$- $%*-+ f!



Common Operators in Java!"#$%& ())*+,% -.,# $%" /)0(*+

J ^^ gg^ hh ^ g ^ g

ii f ! j f !; =;Q =QQQ JQ

; =;Q =QQQ JQ

; =

Notes:• Compare C(/%*8 objects using the -_5'$+BF method, not QQ or JQ• ii and hh use short-circuit evaluation . To see this, say <))$-'* &'*k%8+S$G Q S"TC>

and we evaluate ( &'*k%8+S$G ii ;+)0- R))$-'* -d#/-++%)*= ). Since &'*k%8+S$G isS"TC>, the second part of the expression won’t be evaluated.

• The second operand of j (integer modulus) must be positive.• Don’t compare 6)5<$- s for equality. Instead, define a constant like so:

9%*'$ 6)5<$- >kCWTYO Q Z>geL !! )/ +)0- )(U-/ (U/-+U)$6l !! &U-&: %9 N'(U1'<+B6)5<$-Z 7 6)5<$-\F ; >kCWTYO



Control Structures: Decision (1)• Programs don’t always follow “straight line” execution; they

“branch” based on certain conditions• Java decision idioms: if-then-else, switch• if-then-else idiom:

%9 B;+)0- R))$-'* -d#/-++%)*=FA

!! (':- +)0- '&(%)*M-$+- %9 B;+)0- )(U-/ R))$-'* -d#/-++%)*FA

!! (':- +)0- )(U-/ '&(%)*M-$+-A

!! 6) +)0-(U%*8 -$+-M



Control Structures: Decision (2)• Example:

9%*'$ 6)5<$- YTXPX`YWX Q \1b[ 9%*'$ 6)5<$- O>@PX`YWX Q m1bL6)5<$- 0GX/)%6 Q m1ZL%9 B0GX/)%6 ; YTXPX`YWXF

A CG+(-01)5(1#/%*($*BH"*(%_5-JKFLM-$+- %9 B0GX/)%6 = O>@PX`YWXFA

CG+(-01)5(1#/%*($*BHn-/G 0)6-/*JKFLM-$+-A

CG+(-01)5(1#/%*($*BHo)5/ 6-4%&-p <'/-$G +5##)/(-61KFLM

• Code prints “ n-/G 0)6-/*J ” to the screen.• What if 0GX/)%6 QQ Z1Z? 0GX/)%6 QQ \1] ?



Control Structures: Decision (3)• Example two:

9%*'$ 6)5<$- q>TToPR>"O Q m1Z[ 9%*'$ 6)5<$- WV>PV`>"N Q m1bL9%*'$ 6)5<$- >kCWTYO Q Z>geL6)5<$- 0GX/)%6 Q m1ZL%9 B0GX/)%6 = WV>PV`>"NF

A %9 BN'(U1'<+B0GX/)%6 7 WV>PV`>"NF ; >kCWTYOFA

CG+(-01)5(1#/%*($*BHW&- V/-'0 C'*6I%&UKFLM-$+-A

CG+(-01)5(1#/%*($*BHq-$$G R-'*KFL

MM-$+-A

CG+(-01)5(1#/%*($*BHY$6 4-/+%)*KFLM

• Code prints “ q-$$G R-'* ” to screen. Note nested if-then-else, >kCWTYO usage.



Control Structures: Decision (4)• Other idiom: switch• Only works when comparing an int or boolean

variable against a fixed set of alternatives• Example:%*( '#% Q ZbL

+I%(&U B'#%FA

&'+- ]p CG+(-01)5(1#/%*($*BHV5#&':-KFL </-':L&'+- mp CG+(-01)5(1#/%*($*BHX)*5(KFL </-':L&'+- rp CG+(-01)5(1#/%*($*BHs&$'%/KFL </-':L

&'+- tp CG+(-01)5(1#/%*($*BHS/)G)KFL </-':L&'+- Zbp CG+(-01)5(1#/%*($*BHu%*8-/</-'6KFL </-':L&'+- ZZp CG+(-01)5(1#/%*($*BH?)*-G&)0<KFL </-':L&'+- Zcp CG+(-01)5(1#/%*($*BHW&- V/-'0 C'*6I%&UKFL </-':L&'+- Zep CG+(-01)5(1#/%*($*BHq-$$G R-'*KFL </-':L6-9'5$(p CG+(-01)5(1#/%*($*BHY(U-/KFL </-':L

M



Control Structures: Iteration (1)• Often, blocks of code should loop while a condition holds (or fixed # of times)• Java iteration idioms: while, do-while, for• While loop: execute loop as long as condition is true (checked each iteration)• Example:

C(/%*8 +(/ Q H'''''KL%*( 0%*T-*8(U Q ZbL

IU%$- B+(/1$-*8(UBF ; 0%*T-*8(UFA

+(/ Q +(/ ^ H'KLM

CG+(-01)5(1#/%*($*B+(/FL

• Loop executes 5 times; code terminates when +(/ Q H''''''''''K• Notice: if the length of +(/ was 0%*T-*8(U , the while loop would not

execute



Control Structures: Iteration (2)

While LoopC(/%*8 +(/ Q H''''''''''KL%*( 0%*T-*8(U Q ZbL

IU%$- B+(/1$-*8(UBF ;0%*T-*8(UFA

+(/ Q +(/ ^ H'KLM

CG+(-01)5(1#/%*($*B+(/FL

Do-While LoopC(/%*8 +(/ Q H''''''''''KL%*( 0%*T-*8(U Q ZbL

6)A

+(/ Q +(/ ^ H'KLMIU%$- B+(/1$-*8(UBF ;0%*T-*8(UF

CG+(-01)5(1#/%*($*B+(/FL

Unlike the while loop, the do-while loop executes at least once so long as condition is true.The while loop prints “ '''''''''' ” whereas the do-while loop prints “ ''''''''''' ” (11 ' s)



Control Structures: Iteration (3)• The for loop has the following structure:

9)/ B;-d#/-++%)*Z=L ;-d#/-++%)*\=L ;-d#/-++%)*]=FA

1 1 1M

•

Semantics: – ;-d#/-++%)*Z= is loop initialization (run once) – ;-d#/-++%)*\= is loop execution condition (checked every iteration) – ;-d#/-++%)*]= is loop update (run every iteration)

• Example:

%*( %L9)/ B% Q bL % ; ZbL %^^FA

CG+(-01)5(1#/%*($*BH% Q K ^ %FLMCG+(-01)5(1#/%*($*BH% Q K ^ %FL

• What do you think this code does?



Methods and Design-by-Contract (1)• Design your own methods to perform specific, well-defined tasks• Each method has a signature :

#5<$%& +('(%& `-(5/*.G#- 0-(U)6B#'/'0.G#-Z #'/'0Z[ l #'/'0.G#-O #'/'0OFA

!! #-/9)/0 &-/('%* ('+:M

• Example: a method to compute area of rectangle:#5<$%& +('(%& 6)5<$- 9%*6`-&("/-'B6)5<$- $-*8(U[ 6)5<$- I%6(UFA

/-(5/* $-*8(U f I%6(ULM

• Each method has a precondition and a postcondition – Precondition: constraints method’s caller must satisfy to call method – Postcondition: guarantees method provides if preconditions are met

• For our example: – Precondition: $-*8(U = b1b , I%6(U = b1b – Postcondition: returns $-*8(U v I%6(U (area of rectangle)



Methods and Design-by-Contract (2)• In practice, methods are annotated via JavaDoc,

e.g.,!ff

V)0#5(- '/-' )9 /-&('*8$-1

w#'/'0 $-*8(U T-*8(U )9 /-&('*8$-w#'/'0 I%6(U @%6(U )9 /-&('*8$-w/-(5/* "/-' )9 /-&('*8$-

f!•

Methods called from0'%*BF

(which is+('(%&

)need to be defined +('(%& too• Some methods may not return anything ( 4)%6)



Array Data Structure• Array: fixed-length sequence of variable types; cannot

change length at run-timeExamples:9%*'$ %*( O,NC.,X>O.C Q ZbLC(/%*8DE +(56-*(+L !! X-&$'/'(%)*

C(/%*8DE +(56-*(+ Q *-I C(/%*8DO,NC.,X>O.CEL!! X-&$'/'(%)* '*6 %*%(%'$%x'(%)*C(/%*8DE 0)/-C(56-*(+ Q A H"$%&-K[ HR)<K[ H`)U%(K[ H@-%KML

!! X-&$'/'(%)* '*6 -d#$%&%( %*%(%'$%x'(%)*CG+(-01)5(1#/%*($*B0)/-C(56-*(+1$-*8(UF !! k/%*(+ m

• Enhanced 9)/ loop: executed for each element in arrayExample:9)/ BC(/%*8 +(56-*(p 0)/-C(56-*(+FA CG+(-01)5(1#/%*($*B+(56-*( ^ H[ KFLM

• Prints “ "$%&-[ R)<[ `)U%([ @-%[ ” to screen• Array indices are numbered 0, …, N –1; watch for off-by-one

errors! 0)/-C(56-*(+DbE is “ "$%&-”; 0)/-C(56-*(+D]E is “ @-%”



Two-Dimensional Arrays• We can have two-dimensional arrays.

Example:9%*'$ %*( `Y@C Q ]L 9%*'$ %*( VYT,NOC Q ]L&U'/DEDE (%&.'&.)- Q *-I &U'/D`Y@CEDVYT,NOCEL !! 6-&$'/-9)/ B%*( % Q bL % ; `Y@CL %^^FA 9)/ B%*( 3 Q bL 3 ; VYT,NOCL 3^^F

A(%&.'&.)-D%ED3E Q yPzL !! W*%(%'$%x- () y<$'*:z

MM!! .%&g('&g()- $)8%& 8)-+ U-/- BI%(U y{z+[ yYz+F

• (%&.'&.)-1$-*8(U returns number of rows;(%&.'&.)-DbE1$-*8(U returns number of columns

• Higher-dimensional arrays are possible too



Parameterized Data Structures• We can define data structures in terms of an arbitrary variable type

(call it Item).• "//'GT%+(;W(-0= , a variable-length array that can be modified at

run-time. Examples:"//'GT%+(;C(/%*8= '//C(/%*8+ Q *-I "//'GT%+(;C(/%*8=BFL"//'GT%+(;X)5<$-= '//X)5<$-+ Q *-I "//'GT%+(;X)5<$-=BFL'//C(/%*8+1'66BH"$%&-KFL '//C(/%*8+1'66BHR)<KFL '//C(/%*8+1'66BH`)U%(KFL'//C(/%*8+1'66BH@-%KFLC(/%*8 +(/ Q '//C(/%*8+18-(BZFL !! +(/ <-&)0-+ HR)<K'//C(/%*8+1+-(B\[ H`'3KFL !! H`'3K /-#$'&-+ H`)U%(KCG+(-01)5(1#/%*($*B'//C(/%*8+1+%x-BFFL !! #/%*(+ m

• Notice: – Need to call %0#)/( 3'4'15(%$1"//'GT%+(L at beginning of program –

Off-by-one indexing: cannot call '//C(/%*8+18-(BmFL – Auto-boxing: we cannot create an "//'GT%+( of 6)5<$- s. We need toreplace 6)5<$- with wrapper class X)5<$- . (Recall the “primitive datatypes” table)

• Other parameterized data types include T%+(s, C-( s, N'# s, C('&: s,|5-5- s, ./-- s (see chapters 14–16 in [1])



Exception Handling (1)

• If we had called '//C(/%*8+18-(BmF , wewould have an error condition

– The JVM throws an W*6-dY5(Y9R)5*6+ exception,halts execution



Exception Handling (2)• We handle exceptions using the try-catch-finally structure:

(/GA

!! V)6- (U'( &)5$6 (/%88-/ '* -d&-#(%)*M&'(&U BW*6-dY5(Y9R)5*6+>d&-#(%)* -F !! Y/ '*)(U-/ >d&-#(%)*

A !! V)6- (U'( H/-+#)*6+K () -d&-#(%)*[ -181[-1#/%*(C('&:./'&-BFL

M9%*'$$GA

!! V)6- (U'( -d-&5(-+ /-8'/6$-++ )9 IU-(U-/ -d&-#(%)* )&&5/+M

• There can be many &'(&U blocks for different >d&-#(%)* s, but there is onlyone (/G block and one (optional) 9%*'$$G block. (See Section 7.4 in [1] forthe full “hierarchy” of >d&-#(%)* s)

• Exceptions always need to be caught and “reported”, especially in Android



Outline

• Getting Started• Java: The Basics•

Java: Object–Oriented Programming• Android Programming



Objects and Classes (1)• Classes serve as “blueprints” that describe the states and behaviors of objects ,

which are actual “instances” of classes• For example, a Vehicle class describes a motor vehicle’s blueprint:

– States: “on/off”, driver in seat, fuel in tank, speed, etc. – Behaviors: startup, shutdown, drive “forward”, shift transmission, etc.

• There are many possible Vehicles, e.g., Honda Accord, Mack truck, etc. Theseare instances of the Vehicle blueprint

• Many Vehicle states are specific to each Vehicle object, e.g., on/off, driver inseat, fuel remaining. Other states are specific to the class of Vehicles, not any

particular Vehicle (e.g., keeping track of the “last” Vehicle ID # assigned).These correspond to instance fields and static fields in a class.• Notice: we can operate a vehicle without knowing its implementation “under

the hood”. Similarly, a class makes public instance methods by which objectsof this class can be manipulated. Other methods apply to the set of all Vehicles(e.g., set min. fuel economy). These correspond to static methods in a class



Objects and Classes (2)#5<$%& &$'++ n-U%&$-A

!! W*+('*&- 9%-$6+ B+)0- )0%((-6 9)/ </-4%(GF#/%4'(- <))$-'* %+Y* Q 9'$+-L#/%4'(- <))$-'* %+X/%4-/W*C-'( Q 9'$+-L#/%4'(- 6)5<$- 95-$W*.'*: Q Zb1bL#/%4'(- 6)5<$- +#--6 Q b1bL

!! C('(%& 9%-$6+#/%4'(- +('(%& C(/%*8 $'+(n%* Q Hm"m"k]",fX>}}}}}tKL

!! W*+('*&- 0-(U)6+ B+)0- )0%((-6 9)/ </-4%(GF10(*$- n-U%&$-BF A l M !! V)*+(/5&()/10(*$- 4)%6 +('/(,#BF A l M10(*$- 4)%6 +U5(Y99BF A l M

10(*$- 4)%6 8-(W+X/%4-/W*C-'(BF A l M !! 8-((-/[ +-((-/ 0-(U)6+10(*$- 4)%6 +-(W+X/%4-/W*C-'(BF A l M#/%4'(- 4)%6 0'*'8-N)()/BF A l M !! N)/- #/%4'(- 0-(U)6+ l

!! C('(%& 0-(U)6+10(*$- +('(%& 4)%6 +-(n%*BC(/%*8 *-In%*F A l M

M



Objects and Classes (3)• How to use the n-U%&$- class:

– First, create a new object via constructor n-U%&$-BF, e.g., n-U%&$-0GV'/ Q *-I n-U%&$-BFL

– Change Vehicle states, e.g., +('/(,#BF or +U5(Y99BF the n-U%&$- –

You can imagine other use cases – Mark a new n-U%&$-’s ID number (VIN) as “taken” by callingn-U%&$-1+-(n%*BlF

– Caveat: VINs more complex than this (simple) implementation [7]• Notes:

– Aliasing: If we set n-U%&$- 0G./5&: Q 0GV'/ , both 0GV'/ and 0G./5&: “point” to the same variable. Better to perform “deep copy” of0GV'/ and store the copy in 0G./5&:

– *5$$ reference: refers to no object, cannot invoke methods on *5$$ – Implicit parameter and the (U%+ reference

– Access control: public, protected, private



Inheritance (1)• Types of n-U%&$-s: N)()/&G&$- , V'/ , ./5&: , etc. Types of V'/ s:

C-6'* , V)5#- , C,n . Types of ./5&: s: k%&:5#, S$'(<-6 .• Induces inheritance hierarchy• Subclasses inherit fields/methods from superclasses.• Subclasses can add new fields/methods, override those of

parent classes• For example, N)()/&G&$- ’s 6/%4-S)/I'/6BF method differs

from ./5&: ’s 6/%4-S)/I'/6BF method



Inheritance (2)

#5<$%& &$'++ n-U%&$-A

l#5<$%& 4)%6 6/%4-S)/I'/6

B6)5<$- +#--6FA

!! R'+- &$'++ 0-(U)6M

M

#5<$%& &$'++ N)()/&G&$-+2"+%/3 n-U%&$-

Al#5<$%& 4)%6 6/%4-S)/I'/6

B6)5<$- +#--6FA

!! "##$G #)I-/lM

M

• Inheritance denoted via -d(-*6+ keyword



Inheritance (3)#5<$%& &$'++ ./5&: -d(-*6+ n-U%&$-A

#/%4'(- <))$-'* 5+-"I6 Q (/5-Ll

#5<$%& ./5&:B<))$-'* 5+-"I6F A (U%+15+-"I6 Q 5+-"I6L Ml

#5<$%& 4)%6 6/%4-S)/I'/6B6)5<$- +#--6FA

%9 B5+-"I6FA

!! "##$G #)I-/ () '$$ IU--$+lM

-$+-A!! "##$G #)I-/ () )*$G 9/)*(!<'&: IU--$+l

MM

M



Polymorphism• Suppose we create n-U%&$-s and invoke the 6/%4-S)/I'/6BF method:

n-U%&$- 4-U%&$- Q *-I n-U%&$-BFLn-U%&$- 0)()/&G&$- Q *-I N)()/&G&$-BFL./5&: (/5&:Z Q *-I ./5&:B(/5-FLn-U%&$- (/5&:\ Q *-I ./5&:B9'$+-FL!! V)6- U-/- () +('/( 4-U%&$-+l

4-U%&$-16/%4-S)/I'/6Bc1bFL0)()/&G&$-16/%4-S)/I'/6BZb1bFL(/5&:Z16/%4-S)/I'/6BZc1bFL(/5&:\16/%4-S)/I'/6BZb1bFL

• For 4-U%&$-, n-U%&$-’s 6/%4-S)/I'/6 () method is invoked• For 0)()/&G&$- , N)()/&G&$- ’s 6/%4-S)/I'/6BF method is invoked• With (/5&:Z and (/5&:\ , ./5&: ’s 6/%4-S)/I'/6BF function is invoked

(with all-wheel drive for (/5&:Z , not for (/5&:\ ).• Dynamic method lookup: Java looks at objects’ actual types in determining

which method to invoke• Polymorphism: feature where objects of different subclasses can be treated

the same way. All n-U%&$-s 6/%4-S)/I'/6BF regardless of (sub)class.



The Y<3-&( Class• Every class in Java is a subclass of Y<3-&( • Important methods in Y<3-&(:

– ()C(/%*8BF : Converts the Y<3-&( into a C(/%*8

representation – -_5'$+BF : Compares “contents” of Y<3-&(s to see ifthey’re the same

– U'+UV)6-BF : Hashes the Y<3-&( to a fixed-lengthC(/%*8 , useful for data structures like ?'+UN'# ,?'+UC-(

• If you create your own class, you should override()C(/%*8BF and U'+UV)6-BF



Interfaces• Java interfaces abstractly specify methods to be implemented• Intuition: decouple method definitions from implementations (clean design)• Interfaces, implementations denoted by %*(-/9'&- , %0#$-0-*(+ keywords• Example:

#5<$%& %*(-/9'&- X/%4-'<$-A#5<$%& 4)%6 6/%4-S)/I'/6B6)5<$- +#--6FL

M

#5<$%& &$'++ n-U%&$- %0#$-0-*(+ X/%4-'<$-A

#5<$%& 4)%6 6/%4-S)/I'/6B6)5<$- +#--6F A !! %0#$-0-*('(%)* MM#5<$%& &$'++ N)()/&G&$- -d(-*6+ n-U%&$- %0#$-0-*(+ X/%4-'<$-A

#5<$%& 4)%6 6/%4-S)/I'/6B6)5<$- +#--6F A !! %0#$-0-*('(%)* MM



The V)0#'/'<$- Interface• Comparing Y<3-&(s is important, e.g., sorting in data

structures• The V)0#'/'<$- interface compares two Y<3-&(s, e.g.,

' and <:#5<$%& %*(-/9'&- V)0#'/'<$-A

%*( &)0#'/-.)BY<3-&( )(U-/Y<3-&(FLM

• '1&)0#'/-.)B<F returns negative integer if ' “comes

before” <, b if ' is the same as <, and a positive integerotherwise• In your classes, you should implement V)0#'/'<$- to

facilitate Y<3-&( comparison



Object-Oriented Design Principles• Each class should represent a single concept

– Don’t try to fit all functionality into a single class – Consider a class per “noun” in problem description – Factor functionality into classes, interfaces, etc. that express the

functionality with minimal coupling• For software projects, start from use cases (how customers will use

software: high level) – Then identify classes of interest – In each class, identify fields and methods – Class relationships should be identified: is-a (inheritance), has-a

(aggregation), implements interface, etc.• Packages provide class organization mechanism

– Examples: java.lang.*, java.util.*, etc. – Critical for organizing large numbers of classes! – All classes in a package can “see” each other (scope)



Outline

• Getting Started• Java: The Basics•

Java: Object–Oriented Programming• Android Programming



Introduction to Android• Popular mobile device

OS: 52% of U.S.smartphone market [8]

• Developed by OpenHandset Alliance, led byGoogle

• Google claims 900,000Android deviceactivations [9]

Source: [8]



Android Highlights (1)• Android apps execute on

Dalvik VM, a “clean-room”implementation of JVM

– Dalvik optimized for efficientexecution

– Dalvik: register-based VM,unlike Oracle’s stack-basedJVM

–

Java .class bytecode translatedto Dalvik EXecutable (DEX)

bytecode, which Dalvikinterprets



Android Highlights (2)• Android apps written in Java 5

– Actually, a Java dialect (Apache Harmony) – Everything we’ve learned still holds

• Apps use four main components: – "&(%4%(G: A “single screen” that’s visible to user – C-/4%&-: Long-running background “part” of app ( not

separate process or thread) – V)*(-*(k/)4%6-/ : Manages app data (usually stored in

database) and data access for queries – R/)'6&'+(`-&-%4-/ : Component that listens for particular

Android system “events”, e.g., “found wireless device”,and responds accordingly



App Manifest• Every Android app must include an

"*6/)%6N'*%9-+(1d0$ file describing functionality• The manifest specifies:

– App’s Activities, Services, etc. – Permissions requested by app – Minimum API required – Hardware features required, e.g., camera with

autofocus – External libraries to which app is linked, e.g., Google

Maps library



Activity Lifecycle• "&(%4%(G: key building

block of Android apps• Extend "&(%4%(G class,

override )*V/-'(-BF ,)*k'5+-BF

,)*`-+50-BF

methods• Dalvik VM can stop any

"&(%4%(G without warning,so saving state is important!

• Activities need to be“responsive”, otherwiseAndroid shows user “App

Not Responsive” warning: – Place lengthy operations in

.U/-'6 s, "+G*&.'+: s

Source: [12]



App Creation Checklist• If you own an Android device:

– Ensure drivers are installed – Enable developer options on device under Settings ,

specifically USB Debugging• Android 4.2, 4.3: Go to Settings ! About phone , press Build number

7 times to enable developer options• For Eclipse:

– Make sure you’ve enabled LogCat, Devices views. Click aconnected device in Devices to see its log

– Programs should log states via '*6/)%615(%$1T)8 ’sT)816B"kkP."uPC.`[ H6-<58KF , where "kkP."uPC.` is a9%*'$ C(/%*8 tag denoting your app

– Other commands: T)81-BF (error); T)81%BF (info); T)81IBF (warning); T)814BF (verbose) – same parameters



Creating Android App (1)• Creating Android app

project in Eclipse: – Go to

File ! New ! Other… ,select Android ApplicationProject (Android folder),click Next

– Enter app, project name – Choose package name

using “reverse URL”notation, e.g.,-651)+510G'##

– Select APIs for app, thenclick Next



Creating Android App (2)• Click Next for the next

two windows• You’ll see the “Create

Activity” window.Select “Blank Activity”and click Next.

• Enter Activity’s nameand click Finish

• This automaticallycreates “Hello World”app



Deploying the App• Two choices for deployment:

– Real Android device – Android virtual device

• Plug in your real device;otherwise, create an Androidvirtual device

• Emulator is slow. Try Intelaccelerated version, or perhapsU((#p!!III18-*G0)(%)*1&)0!

• Run the app: right click projectname, select Run As ! Android

Application



Underlying Source Code

#'&:'8- -651)+51U-$$)'*6/)%6L

%0#)/( '*6/)%61)+1R5*6$-L%0#)/( '*6/)%61'##1"&(%4%(GL%0#)/( '*6/)%614%-I1N-*5L

#5<$%& &$'++ N'%*"&(%4%(G -d(-*6+ "&(%4%(GAwY4-//%6-#/)(-&(-6 4)%6 )*V/-'(-BR5*6$- +'4-6W*+('*&-C('(-FA

+5#-/1)*V/-'(-B+'4-6W*+('*&-C('(-FL+-(V)*(-*(n%-IB`1$'G)5(1'&(%4%(GP0'%*FL

M

wY4-//%6-#5<$%& <))$-'* )*V/-'(-Y#(%)*+N-*5BN-*5 0-*5FA

!! W*9$'(- (U- 0-*5L (U%+ '66+ %(-0+ () (U- '&(%)* <'/ %9 %( %+ #/-+-*(18-(N-*5W*9$'(-/BF1%*9$'(-B`10-*510'%*[ 0-*5FL/-(5/* (/5-L

MM

3#-4546,$%7-"$8$"9:;,8,



Underlying GUI Code

;`-$'(%4-T'G)5( d0$*+p'*6/)%6Q !"##$%&&'(")*+',+-./01.,(0*&+$2&/)'&+-./01.!d0$*+p())$+Q !"##$%&&'(")*+',+-./01.,(0*&#004'!'*6/)%6p$'G)5(PI%6(UQ !*+#("5$+/)-#!'*6/)%6p$'G)5(PU-%8U(Q !*+#("5$+/)-#!

'*6/)%6p#'66%*8R)(()0Q !6.1*)-&+(#171#857)/#1(+45*+/91-!'*6/)%6p#'66%*8T-9(Q !6.1*)-&+(#171#85"0/1:0-#+45*+/91-!'*6/)%6p#'66%*8`%8U(Q !6.1*)-&+(#171#85"0/1:0-#+45*+/91-!'*6/)%6p#'66%*8.)#Q !6.1*)-&+(#171#857)/#1(+45*+/91-!())$+p&)*(-d(Q !,;+1-<(#171#8! =

;.-d(n%-I'*6/)%6p$'G)5(PI%6(UQ !>/+$5(0-#)-#!'*6/)%6p$'G)5(PU-%8U(Q !>/+$5(0-#)-#!'*6/)%6p(-d(Q !6'#/1-9&")4405>0/4.! &=

;!`-$'(%4-T'G)5(=

#+34*,9)0"4,-"$8$"9<=,$%:2=*

–`-$'(%4-T'G)5(

s are quite complicated. See [13] for details



The App Manifest;~d0$ 4-/+%)*Q !?,@! )-(0.1-9A!B#CDE!F=;0'*%9-+( d0$*+p'*6/)%6Q !"##$%&&'(")*+',+-./01.,(0*&+$2&/)'&+-./01.!

#'&:'8-Q !).B,0'B,")440+-./01.!'*6/)%6p4-/+%)*V)6-Q !?!'*6/)%6p4-/+%)*O'0-Q !?,@! =

;5+-+g+6:

'*6/)%6p0%*C6:n-/+%)*Q !E!'*6/)%6p('/8-(C6:n-/+%)*Q !?G! &=

;'##$%&'(%)*'*6/)%6p'$$)IR'&:5#Q !#/B)!'*6/)%6p%&)*Q !6./+>+H4)&1(54+B-(")/!'*6/)%6p$'<-$Q !6'#/1-9&+$$5-+*)!'*6/)%6p(U-0-Q !6'#84)&<$$I")*)! =;'&(%4%(G

'*6/)%6p*'0-Q !).B,0'B,")440+-./01.,;+1-<(#171#8!'*6/)%6p$'<-$Q !6'#/1-9&+$$5-+*)! =;%*(-*(g9%$(-/=

;'&(%)* '*6/)%6p*'0-Q !+-./01.,1-#)-#,+(#10-,;<JK! &=;&'(-8)/G '*6/)%6p*'0-Q !+-./01.,1-#)-#,(+#)90/8,L<MKNOPQ! &=

;!%*(-*(g9%$(-/=;!'&(%4%(G=

;!'##$%&'(%)*=;!0'*%9-+(=

7%/#)$/6,%$>+3":2=*



A More Interesting App• We’ll now examine an

app with more features:WiFi Tester (code on

class website)• Press a button, scan for

WiFi access points(APs), display them



Underlying Source Code (1)wY4-//%6-10(*$- 8)$/ )%?#+,"+@A0%/*+ 3,8+/B%3",%-+!","+CA

301+#:)%?#+,"+@3,8+/B%3",%-+!","+CD+-(V)*(-*(n%-IB`1$'G)5(1 +(#171#85>15C1RS

!! C-( 5# @%9%N'*'8-/10@%9%N'*'8-/ Q B@%9%N'*'8-/F 8-(CG+(-0C-/4%&-BV)*(-d(1 TJUJ5VPQWJNPRS

!! V/-'(- $%+(-*-/ )<3-&( 9)/ R5(()*1 @U-* R5(()* %+ #/-++-6[ +&'* 9)/!! "k+ *-'/<G1R5(()* <5(()* Q BR5(()*F 9%*6n%-IRGW6B`1%61 HB##0-RS<5(()*1+-(Y*V$%&:T%+(-*-/B %+E F$+E:G%?*$-HI$3"+%+#@CA

10(*$- 8)$/ )%?*$-H@F$+E 8CA

())*+,% 3-,%!",#"+/ J =K$>$6,%,&+#:3",#"!-,%@CD

!! W9 (U- +&'* 9'%$-6[ $)8 %(1$> @L3-,%!",#"+/C I)&: !"#$%& ()*+* ,-./ 0.*1!2333(45

MMFL

!! C-( 5# W*(-*(S%$(-/ 9)/ •@%S% +&'* /-+5$(+ '4'%$'<$-• W*(-*(10W*(-*(S%$(-/ Q %+E B%"+%"M$*"+#@CD0W*(-*(S%$(-/1'66"&(%)*B@%9%N'*'8-/1 VN<K5QPVMLIV5<W<JL<XLP5<NIJYKRS

M



Underlying Source Code (2)• Code much more complex• First get system @%9%N'*'8-/• Create listener Y<3-&( for button that

performs scans• We register Broadcast Receiver,

0`-&-%4-/ , to listen for@%9%N'*'8-/ ’s “finished scan” systemevent (expressed as W*(-*( @%9%N'*'8-/1CV"OP`>C,T.CP"n"WT"RT>P"V.WYO)

• Unregister Broadcast Receiver whenleaving "&(%4%(G

wY4-//%6-1#)"+-"+/ 8)$/ )%N+30=+@CA

301+#:)%N+30=+@CD/-8%+(-/`-&-%4-/B0`-&-%4-/[

0W*(-*(S%$(-/FLM

wY4-//%6-1#)"+-"+/ 8)$/ )%O,03+@CA

301+#:)%O,03+@CD

5*/-8%+(-/`-&-%4-/B0`-&-%4-/FLM



The Broadcast Receiver#/%4'(- 9%*'$ R/)'6&'+(`-&-%4-/ 0`-&-%4-/ Q *-I R/)'6&'+(`-&-%4-/BFA

wY4-//%6-#5<$%& 4)%6 )*`-&-%4-BV)*(-d( &)*(-d([ W*(-*( %*(-*(FA

C(/%*8 '&(%)* Q %*(-*(18-("&(%)*BFL%9 B@%9%N'*'8-/1CV"OP`>C,T.CP"n"WT"RT>P"V.WYO1-_5'$+B'&(%)*FFA

T)81-B."u[ •C&'* /-+5$(+ '4'%$'<$-•FLT%+(;C&'*`-+5$(= +&'*`-+5$(+ Q 0@%9%N'*'8-/18-(C&'*`-+5$(+BFL0"#C(/ Q ••L9)/ BC&'*`-+5$( /-+5$( p +&'*`-+5$(+FA

0"#C(/ Q 0"#C(/ ^ /-+5$(1CCWX ^ •L •L0"#C(/ Q 0"#C(/ ̂ /-+5$(1RCCWX ̂ •L •L0"#C(/ Q 0"#C(/ ̂ /-+5$(1&'#'<%$%(%-+ ̂ •L •L

0"#C(/ Q 0"#C(/ ^ /-+5$(19/-_5-*&G ^ • N?xL•L0"#C(/ Q 0"#C(/ ̂ /-+5$(1$-4-$ ̂ • 6R0a*a*•LM!! ,#6'(- ,W () +U)I '$$ (U%+ %*9)/0'(%)*1+-(.-d(n%-IB0"#C(/FL

MM

ML



User InterfaceUpdating UI in code

1#$8,"+ 8)$/ 3+"P+2"F$+E@!"#$%& 3"#CA

.-d(n%-I (4 Q B.-d(n%-IF9%*6n%-IRGW6B`1%61#)Z#71)>R L

(41+-(N)4-0-*(N-(U)6B %+E!-#)**$%&6)8+=+%"6+".)/@CCD

(41+-(.-d(B+(/FLM

• This code simply has the UI displayall collected WiFi APs, makes thetext information scrollable

UI Layout (XML);T%*-'/T'G)5( d0$*+p'*6/)%6Q !"##$%&&'(")*+',+-./01.,(0*&+$2& /)'&+-./01.!

d0$*+p())$+Q !"##$%&&'(")*+',+-./01.,(0*&#004'!'*6/)%6p$'G)5(PI%6(UQ !C1445$+/)-#!'*6/)%6p$'G)5(PU-%8U(Q !C1445$+/)-#!'*6/)%6p)/%-*('(%)*Q !7)/#1(+4!=

;R5(()*'*6/)%6p$'G)5(PI%6(UQ !C1445$+/)-#!'*6/)%6p$'G)5(PU-%8U(Q !>/+$5(0-#)-#!'*6/)%6p%6Q !6[1.&HB##0-!'*6/)%6p(-d(Q !6'#/1-9&HB##0-5#)Z#!&=

;.-d(n%-I'*6/)%6p%6Q !6[1.&")+.)/!'*6/)%6p$'G)5(PI%6(UQ !C1445$+/)-#!'*6/)%6p$'G)5(PU-%8U(Q !>/+$5(0-#)-#!'*6/)%6p(-d(Q !6'#/1-9&+$541'#!())$+p&)*(-d(Q !,T1U1<(#171#8!'*6/)%6p(-d(C(G$-Q !H04.!

'*6/)%6p8/'4%(GQ !()-#)/!=;!.-d(n%-I=

;.-d(n%-I'*6/)%6p$'G)5(PI%6(UQ !C1445$+/)-#!'*6/)%6p$'G)5(PU-%8U(Q !C1445$+/)-#!())$+p&)*(-d(Q !,T1U1<(#171#8!'*6/)%6p%6Q !6[1.&#)Z#71)>!'*6/)%6p+&/)$$<'/+Q !7)/#1(+4!=

;!.-d(n%-I=;!T%*-'/T'G)5(=



Android Programming Notes• Android apps have multiple points of entry: no 0'%*BF method

– Cannot “sleep” in Android – During each entrance, certain Y<3-&(s may be *5$$ – Defensive programming is very useful to avoid crashes, e.g.,

%9 BJB0GY<3 QQ *5$$FF A !! 6) +)0-(U%*8 M• Java concurrency techniques are required

– Don’t block the “main” thread in Activities – Implement long-running tasks such as network connections

asynchronously, e.g., as "+G*&.'+: s – Recommendation: read [4]; chapter 20 [10]; [11]

• Logging state via '*6/)%615(%$1T)8 throughout app is essentialwhen debugging (finding root causes)

• Better to have “too many” permissions than too few – Otherwise, app crashes due to security exceptions! – Remove “unnecessary” permissions before releasing app to public

• Event handling in Android GUIs entails many listener Y<3-&(s



Concurrency: .U/-'6 s (1)• .U/-'6 : program unit (within process) executing independently• Basic idea: create class that implements `5**'<$- interface

– `5**'<$- has one method, /5*BF , that contains code to be executed – Example:

#5<$%& &$'++ Y5/`5**'<$- %0#$-0-*(+ `5**'<$-A #5<$%& 4)%6 /5*BF

A!! /5* &)6-

MM

• Create a .U/-'6 object from `5**'<$- and +('/(BF .U/-'6 , e.g.,`5**'<$- / Q *-I Y5/`5**'<$-BFL.U/-'6 ( Q *-I .U/-'6B/FL(1+('/(BFL

• Problem: this is cumbersome unless .U/-'6 code is reused



Concurrency: .U/-'6 s (2)• Easier approach: anonymous inner classes, e.g.,

.U/-'6 ( Q *-I .U/-'6B*-I `5**'<$-BA

#5<$%& 4)%6 /5*BFA

!! &)6- () /5*MMFL

(1+('/(BFL• Idiom essential for one-time network connections in

Activities• However, Threads can be difficult to synchronize,

especially with UI thread in Activity. AsyncTasks are better suited for this



Concurrency: AsyncTasks• "+G*&.'+: encapsulates asynchronous task that interacts with UI thread

in "&(%4%(G:#5<$%& &$'++ "+G*&.'+:;k'/'0+[ k/)8/-++[ ̀ -+5$(=A

#/)(-&(-6 ̀ -+5$( 6)W*R'&:8/)5*6Bk'/'0.G#- #'/'0FA

!! &)6- () /5* %* <'&:8/)5*6#5<$%+Uk/)8/-++Bk/)8/-++.G#- #/)8/-++FL !! ,Wl/-(5/* ̀ -+5$(L

M

#/)(-&(-6 4)%6 )*k/)8/-++,#6'(-Bk/)8/-++.G#- #/)8/-++FA !! %*4):- 0-(U)6 %* "&(%4%(G () 5#6'(- ,WM

M• Extend "+G*&.'+: with your own class• Documentation at http://developer.android.com



Thank You

Any questions?



References (1)1. C. Horstmann, Big Java Late Objects , Wiley, 2012. Online: http://proquest.safaribooksonline.

com.proxy.lib.ohio–state.edu/book/–/9781118087886 2. J. Bloch, Effective Java , 2nd ed., Addison–Wesley, 2008. Online: http://proquest.

safaribooksonline.com.proxy.lib.ohio–state.edu/book/programming/java/9780137150021 3. S.B. Zakhour, S. Kannan, and R. Gallardo, The Java® Tutorial: A Short Course on the Basics ,

5th ed., Addison–Wesley, 2013. Online: http://proquest.safaribooksonline.com.proxy.lib.ohio–state.edu/book/programming/java/9780132761987

4. C. Collins, M. Galpin, and M. Kaeppler, Android in Practice , Manning, 2011. Online:http://proquest.safaribooksonline.com.proxy.lib.ohio–state.edu/book/programming/android/9781935182924

5. M.L. Sichitiu, 2011, http://www.ece.ncsu.edu/wireless/MadeInWALAN/AndroidTutorial/PPTs/ javaReview.ppt

6. Oracle, http://docs.oracle.com/javase/1.5.0/docs/api/index.html 7. Wikipedia, https://en.wikipedia.org/wiki/Vehicle_Identification_Number 8. Nielsen Co., “Who’s Winning the U.S. Smartphone Market?”, 6 Aug. 2013,

http://www.nielsen.com/us/en/newswire/2013/whos-winning-the-u-s-smartphone-market-.html

9. Android Open Source Project, http://www.android.com



References (2)10. http://bcs.wiley.com/he-bcs/Books?action=index&itemId=1118087887&bcsId=7006 11. B. Goetz, T. Peierls, J. Bloch, J. Bowbeer, D. Holmes, and D. Lea, Java Concurrency in

Practice, Addison-Wesley, 2006, online athttp://proquest.safaribooksonline.com/book/programming/java/0321349601

12. https://developer.android.com/guide/components/activities.html

13.

https://developer.android.com/guide/topics/ui/declaring-layout.html#CommonLayouts

java android programming

Documents