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86 Cards in this Set

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Is java case sensetive?


Does java ignore overflow and underflow?

- Java is case sensetive


- java does ignore underflow and over flow


( this means that an integer incremented at maximum value will loop back to minimum value)



What does the declaration of a variable do?

- arranges for space to be allocated for the variable


- ensures only valid operators can be performed on this variable

What is the difference (syntactically) between declaring a variable and initializing a variable?

Declaration:


int cars;


Initialization (first assignment):


int cars = 5;


assignment:


cars = 6;




In java, a variable can only be declared once. (probably within same method)

compare strings using...?

obj.equals("string");




NOT ==

Formula for comparing doubles

what is the output?

what is the output?

"seven"

3 things happen with evaluation of this




double cars = new double[250]

1. Allocates 250 double precision storage locations


2. variable 'cars' stores the first location


3. initializes each 250 locations to 0.0



What is the output?




What is the output?

"CS 1234"




alice points to what alicia is pointing to


(which is the first location of the string array alicia)

ArrayList jim = new ArrayList();




what is command to add "tom" to array list Jim at first location?

jim.add(0,"tom");

1. What is a method signature?


2. How does it relate to overloaded methods?

1. A method signature is the Method Name, parameter types




NOT method type!


2. to overload methods, must have variance in method signature

method parameters are located ...

public int print(PARAMETER HERE) {


}

arguments are located...

main {


Jim j = new Jim(ARGUMENTS HERE) ;



}

What is an interface, and why is it used?

A interface is like an agreement to implement certain method signatures.




The methods signatures within the interface do not have bodies.

Can interfaces be instantiated?

location 8780

location 8780

what is an abstract method?

used in interfaces

used in interfaces

What 3 things can an interface NOT have?

Cannot have


1. method bodies (use abstract method)


2. fields ( other than constants)


3. static methods (because why would an interface need functional methods?)

Fields in interfaces are implicitly declaired..?

public, final, & static




they must be declared with an initializer(=)




(methods are implicitly public)

If a field in an interface(a constant) is changed, what value will the dependent classes see?

the updated value

A class can implement how many interfaces? Extend how many parent classes?

implement MANY


extend ONE

what is a prerequisite to be able to use a for each loop

what is a prerequisite to be able to use a for each loop

"list" must implement the ITERABLE interface

what is a field?

an attribute of an OBJECT or THE CLASS



what is a method?

an operation on an OBJECT or THE CLASS

what is static vs non static?

static is 'of the class':


(static field) one memory location/value shared by all objects of class




non-static is 'of the/an object'

Variables:


what is an instance variable?


class variable?


local variable?

instance variable: non-static fields in a class declaration




Class variables: static fields in a class declariation




local variables: variables in a method or block

what may only access static fields and call other static methods?




can be called using the class name

static methods

what is a good rule of thumb for scope of a variable?




scope is visivility (think teleSCOPE)

the variable is usable from the point it is declared to the end of the block

public void (int x) {
int x = 0;


}




is this legal?

nope

nope

example of field hiding



what is "this"

reference to current object

when does an object of reference type die?

when there is nothing pointing to it!

what is the output

what is the output

42


-1




the address is sent


- x points to the first location of the array list


- a then points to the first location of the array list


a can then modify the value without.




notice this way you can modify an array without having to have a method return anything




does not work on int, Integer, double, Double..



definition of encapsulation and why its important.

encapsulation is hiding information and methods that completes a task so that an end user experiences only the final output and does not have to worry about how the computation took place. This is good in team settings when programs get large and chunks of code need to be abstracted to a single line.

difference between access modifiers:


public?


private?


protected?

public: fields/methods can be accessed from outside the class (NO restriction)




private: fields/methods can NOT be directly accessed from outside the class




protected: seen in class, subclass (even if subclass is in a different package) , same package

what is a checked exception

- needs to be caught/handled before compilation time




- reminder from compiler to programmer about potential failure state




- subclass of Exception




ex: IOException, DataAccessException

What is an Unchecked Exception

- not checked at compile time.


- generally programming error


ex: lovely NullPointerException


ArrayIndexOutOfBounds




- subclass of RunTimeException

convention for access modifiers

field are private, can have getters/setters




methods are public

can you have an ArrayList




(of primative types)?

no! however, can have ArrayList




Integer being the wrapper class for int





.length() is for ?




.lenght is for ?

- String.length();




int[] d = new int[3];


- d.length;

in sub-class constructor...

super is called first, implicitly if not specified




think: the parent must exist before the child, to make the parent, then create child

True/False


In one constructor method, you can call both


- super()


and


-this()



False!

instance of operator

all objects are instances of Object

all objects are instances of Object

what is the call stack?

- Each method is a frame.

- Each frame holds storage for parameters and local variables of the method.

- Each method is a frame.




- Each frame holds storage for parameters and local variables of the method.

syntax of a basic try/catch block..

 - 'Exception' is a class name

this one is just catching the most generic exception which is Exception

- 'Exception' is a class name




this one is just catching the most generic exception which is Exception



what does a method do 'syntatically' when it doesnt want to handle the exception, but pass the problem to someone else , like an incompetent *******



what is needed to write ones own exception?



what is the trend in catch blocks?

specific to general

Finally clause....

executes no matter what!

domain decomposition

a way of splitting up tasks with threads in which the same code processes different sub-domains

task decomposition

a way of splitting up task with threads based on nature of the task




one thread handle graphics in GUI


other thread handle backend code

if we have, Thread t;




t.join()




does what?

blocks the CURRENT THREAD until thread t completes.



is generally in try/catch


for InterruptedException


important that threads synchronize on same object




example , if threads are of one class




have a class variable,


private static Object gatekeeper = new Object();

thread state map



importance of buffering

decreases amount of read calls necessary.




reads 'more than needed'




important to flush buffers!

FileOutputStream

low level I/O




handles: raw data, byte-oriented

DataOutputStream

High level I/O




handles: java primitive types



ObjectOutputStream

Object I/O




handles: java objects

DataOutputStream




and




ObjectOutputStream




need to build off?

- FileOutputStream takes file as arguement


- Data/Object output takes FileOutput obj as arguement



. class is compiled version of .java

.class in not human readable




.java is

read/write from a text file

read:


BufferedReader r = new BufferedReader(new FileReader(file object));




write:


PrintWriter w = new PrintWriter(new FileOutputStream( new File ("filename")));





Internet Protocol

128.10.2.21


identifies host


a computer

Domain Name System

maps


128.10.9.143


to


data.cs.purdue.edu

Transmission Control Protocol

identifies ports on hosts for a network connection

Socket

Ip address + TCP port




house + streetname

how many sockets make a connection?

2

Servers wait for connection

One physical device can be both server and client, at different times







ServerSocket has .accept() method that waits




accept returns a Socket object

kool

to implement server with many client connection. And avoid blocking client connections

use threads



if we wanted to downcast a3 from Animal to Bird,

what must be done to make sure this will not yield errors?

if we wanted to downcast a3 from Animal to Bird,




what must be done to make sure this will not yield errors?

In dynamic binding, the method called depends on the...




dynamic binding occurs during...

class of the object referenced


runtime


(overriding methods, dynamic binding)

Animal myanimal = new SongBird();

is 
myanimal.sing(); 
legal?

Animal myanimal = new SongBird();




is


myanimal.sing();


legal?

NO! animal does not know how to sing

Animal myanimal = new SongBird();

is
myanimal.move();
legal?

Animal myanimal = new SongBird();




is


myanimal.move();


legal?

Yes, but interestingly SongBird does not have a move method so we go up the inheritance hierarchy and find that Bird overrides the move()


so "flying" would be printed, or something

In static binding, the method called depends on the ...




static binding occurs during

class of the variable




compilation time

output?

output?

inside Collection sort method




because variable type was of Collection

String s = "Guybrush";




s.substring(2,4) = ??

"yb" stop at 4-1

what happens if your exceptions are listed generic to specific?

compilation error, unreachable code

compilation error, unreachable code



know



in javax.swing




modal - wait until closed to continue program




JFileChooser

Dynamic Data Structures offer....

fluidity

Abstract Data Type

- exhibit a behavior, dont know how implemented


-stack


-queue


ex:


stack implemented via linkedList or array

stack

-pop


-push


-isEmpty




Last In First Out

queue

- add


- remove


- peek

ex print que

First In First Out


break the problem down into two pieces


- basis case:


- recursice case:



recursion

recursion

watch out for how many frames are made




proxy method to call recursive method



traversing a binary search tree