Ch. 5 Flashcards by Jake Convery

| What is an object reference variable?

| A variable that points to some location in the computer's memory

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| What happens if we make a reference variable with no object in it?

| It becomes a null object

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| How do you determine if an object is null?

You need to make an if statement in the object with a println. Like, if it is null, then something will be printed

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| What type of variable is an instance variable?

| Null

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| What happens if you follow a null reference?

| You get a NullPointerException because the object is not initialized

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| What does a NullPointerException allow?

| A method to refer to its own object, like refering to myself as I

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| What are multiple references to the same object called?

| Ailiases

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| What happens when an assignment operation is used with object references?

| The memory location is copied

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| What happens if an object's state is changed through a reference?

| The sate of the object for all references is changed

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| Why does changing one reference change all references?

| They all point to the same location in memory

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| What happens if you use == to test object references for equality?

| It tests to see if the aliases are the same. You need to do nam1.equals(name2)

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| What happens to parameters in Java?

| They are passed by value

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| What happens when we pass an object into a method?

| It becomes an alias of the formal parameter

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| What is a static method?

| One that does not require an object. Just do class.method()

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| What type of methods are the entire math class?

| Static

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| What is a static variable like?

<p style="text-align: center;">
	They are not tied to a particular object, they are a class variable</p>

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| What happens when static variables are loaded with the class?

| Space is created for them because they will be used thorughout the class

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| What are static variables most commonly used for?

| Constraints

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| What can be interchanged in static methods?

| The modifiers, but usually the visibility ones are put furst anyway

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| How is the main method static?

| It is invoked without creating an object

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| What kinds of variables can be used with static methods?

| Static variables or local variables. NO INSTANCE VARIABLES

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| What is the chain of exceptions?

| A program throws exceptions which are caught or handled by other parts of the program

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| What is an exception?

| A part of a program that describes an unusual or erroneous sistuation

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| How is a program divided?

| The normal execution flow and the exception execution flow

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| What is an error in java?

| An object that may sometimes represent an unrecoverable situtation and should not be caught

| What is "Not Responding"?

| An error that is trying to be caught but it's not really working out

| What must a programmer always ensure?

| An object reference variable refers to a valid object

| What is a this reference?

| When an object refers to itself

| What does java have for when something goes wrong?

| A built in set of exceptions

| What can we make to go off whenever we want?

| Our own exceptions

| How are exceptions handled?

| Ignoring it, handling it where it occurs, and handling it somewhere else in the program

What happens when an exception is ignored?

The program crashes and returns an appropriate message

What happens when an exception is handled where it occurs?

The user is promted to fix whatever is wrong. This is the best way to do things

What is call stack trace?

Laying out where the exception occured to show where the program was when the crash occured for troubleshooting and shows the method call trail right before the crash

Where are exception throw statements found?

Nested in if satements to determine if an exception should be thrown

How do you throw an exception?

throw new NameException()

What is an interface?

A collection of abstract methods and constants, where a header is provided but not a body

What are all methods in an interface by default?

Abstract

What is an interface like?

A to do list for a class, like saying we need these methods but we don't actually make them

What can't you do with interfaces?

Instantiate them because they're not objects

What type of visibility do interface methods have by default?

Public

What is required for interfaces?

The methods stated in it need to be defined elsewhere

What is implementing an interface?

Actually doing the math and spelling things out

What can an interface contain?

Constants

What may an interface's class contain?

Multiple interfaces

how do you set up an interface?

class ClassName implements interface1, interface2

What must a programmer decide?

How to define an interface's abstrac method?

What comes with Java?

A prewritten interface with a list of abstract methods

What is implemented with the list interface?

Classes that contain an ordered collection of elements

What is defined with the comparable interface?

the compareTo method which is used to compare stuff

What does an iterator do?

Allow a user to move easily through a collection of objects, doing something with each object

What is usually used with Compareable?

A string compared via lexiographic ordering

What is the comparable test?

if obj1obj2, 1

How fast do iterators work?

1 thing at a time

What does the Next method do?

Return the next object in the iteration

What does the hasNext method do?

Return a boolean that is true when there is nothing left to process

What do objects usually represent?

Nouns

What do classes represent?

Object groups with similar behaviors

What is necessary in a class>

General and specific classes... ie not too much in a class

what is state?

Something's representation

What is behavior?

What it does

What is a nested class?

A class within a class

What is the enclosed and outer class?

Enclosed is the nested class, outer is the nested class host

What is a nested class like?

A huge class that accesses all of the variable in the enclosing class

How is a nested class protected?

The outer class can prevent data leaking

What is separated with an enclosed and outer class?

The bytecode files

What types of objects compose a gui?

components, events, and listeners

What is a gui component?

the pieces that put together a gui, like buttons and menus

What is a gui event>

What we do with the computer, like typing and moving arond the mouse

What does the gui listener do?

What actually does something, like running code