AP Computer Science A

Terms in this set (303)

AP CS A concerns _______-__________ programming.

object-oriented

Related classes in java are grouped into...

A Java program must have at least ___ class(es).

The java files that comprise your program are called...

A __________ converts source code into a machine readable form.

A compiler converts source code into a machine readable form, called...

All Java methods must be contained in a(n)...

All program statements must be placed inside a(n)...

The keyword _____ signals that the class or method is usable outside the class.

The keyword ____ signals data or methods are not usable outside the class.

The keyword ________ is used for methods that will not access any objects of a class.

The ________ method must always be static.

A(n) ____ is a name for a variable, parameter, constant, user-defined method, or user-defined class

An identifier may use... (3)

letters, digits, and underscores

Identifiers may not begin with a(n)...

What primitive types are included in the AP Java subset? (4)

int, boolean, double, char

If you try to store a value that is too big in an int variable, you'll get a(n)....

When you get an overflow error, does Java give you a warning?

Assigning a double to an int will cause a(n)...

compile-time error

A(n) ________ variable is used to name a quantity whose value will not change.

True or false: constant identifiers are capitalized.

What purpose does using constants serve?

it makes it easier to revise the code

_____________ operators are used in boolean expressions.

Relational operators should generally only be used when comparing...

primitive types

Avoid using boolean operators to compare ______-______ numbers.

_________ operators are applied to boolean expressions to form compound boolean expressions.

What logical operator does the following truth table correspond to?

? | T F
--------------
T | T F
F | F F

What logical operator does the following truth table correspond to?

? | T F
--------------
T | T T
F | T F

What logical operator does the following truth table correspond to?

? | T
-----------
T | F
F | T

Operators such as +=, =, -=, and /= are known as __________ operators.

compound assignment

True or false: when chain assignments like the following are used:

x = y = z = 0;

the statement is evaluated from left to right.

Is the following order of operator precedence correct?

1) !, ++, --
2) *, /, %
3) +, -
4) <, >, <=, >=
5) ==, !=
6) &&
7) ||
8) =, +=, -=, *=, /=, %=

What will be the output of the following statement?

System.out.println( 5 + 3 < 6 - 1 );

_________ is an object in the System class that allows output to be displayed on the screen.

The ______ method outputs an item and then goes to a new line.

The ________ method outputs an item without going to a new line afterward.

A(n) _________ __________ is a backslash followed by a single character.

escape sequence

What are escape sequences used for?

to print special characters

What are the three escape sequences necessary to know for the AP exam?

_______ __________ are the mechanism by which you make the statements of a program run in non-sequential order.

control structures

if, if-else, nested if, and extended if statements are all known as ______-______ control structures.

decision-making

Name the two control structures that allow the computer to perform iterative tasks.

for loop and while loop

The following is known as what kind of loop?

for (SomeType element : collection)
{
statements;
}

A(n) __________ is an error condition that occurs during the execution of a Java program.

If you divide an integer by zero, what kind of error is thrown?

ArithmeticException

If you use a negative array index, what kind of error is thrown?

ArrayIndexOutOfBoundsException

An ________ exception is one where you don't provide code to deal with the error.

A(n) __________ exception is thrown to indicate that a parameter does not satisfy a method's precondition

IllegalArgumentException

A(n) ______ is a software blueprint for implementing objects of a given type

A(n) ________ is a single instance of a class.

The current state of a given object is maintained in its ____ ______ or _______ _________.

data fields; instance variables

The ________ of the class provide behaviors exhibited by an object and the operations that manipulate the object

Combining an object's data and methods into a class is known as...

In the AP Java subset, all classes are...

A ____ ___________ contains a value that is shared by all instances of the class

static variable

Give the formula for a method header.

access specifier, return type, method name, parameter list

A(n) _______ creates an objects of the class.

A constructor's name is always the same as...

A constructor has no...

A(n) _________ constructor has no arguments.

Getter methods are also known as...

accessor methods

Setter methods are also known as...

mutator methods

A(n) _______ method accesses a class object without altering the object

A(n) ________ method changes the state of an object by modifying at least one of its instance variables.

A method that performs an operation for the entire class, not its individual objects, is called a(n)...

All methods defined in the main program must be...

________ methods are two or more methods in the same class that have the same name but different parameter lists.

A method's signature consists of...

the method name and parameter types

The compiler figures out which method to call by examining a method's...

True or false: you can't have two methods with identical signatures but different return types.

Having more that one constructor in the same class is an example of...

The _____ of a variable or method is the region in which that variable or method is visible and can be accessed.

A(n) ______ variable is defined inside a method.

A ________ is a piece of code enclosed in a {} pair.

When a block is exited, the memory for a local variable is...

True or false: local vars take precedence over instance vars with the same name

In the method obj.doSomething(x); "obj" is a(n) ______ parameter and "x" is a(n) ________ parameter.

explicit, implicit

Whereas double, int, char and boolean are primitive data types, all objects are ______ data types.

Having two references for the same object is known as...

An uninitialized object variable is called a...

null reference/null pointer

An attempt to invoke an instance method with a null reference may throw a...

NullPointerException

The parameters used in a method heading are known as _____ or ________ parameters.

The parameters one uses when actually using a method are known as _______ parameters or __________.

actual, arguments

____________ are passed by value

What does it mean for primitive types if parameters are passed by value?

when a method is called, a new memory slot is allocated for each parameter

In Java, both ___________ _________ and _______ __________ are passed by value.

primitive types; object references

What happens when an object is passed as a parameter?

The address is copied into local memory, but not the values of the instance variables

Define inheritance.

the mechanism by which a new class, called a subclass, is created from an existing class, called a superclass; by absorbing its state and behavior and augmenting these with features unique to the new class.

Which is bigger: a subclass or a superclass?

a subclass; it contains more data and more methods

A subclass can itself be a superclass for another subclass, leading to a(n)...

inheritance hierarchy

The relationship that a subclass has to its superclass is informally referred to as a(n)...

is-a relationship

True or False: a subclass cannot redefine a method that it inherits.

If part of the original method from the superclass is retained, we refer to the subclass's rewrite as...

partial overriding

What is the format of implementing a subclass?

public class Subclass extends Superclass

True or false: subclasses inherit the private instance variables and private methods of their superclasses.

True or false: subclasses can only access the public methods of their superclasses.

How can a subclass override a method from its superclass?

by defining a method with the same return type and signature

What keyword is necessary in order to invoke a method from a superclass?

True or false: Private methods from superclasses cannot be overridden in subclasses.

Are constructors from superclasses inherited by subclasses?

How can a subclass constructor implement its instance variables exactly the same way as the superclass constructor?

by using the super() method

If super is used in the implementation of a subclass constructor, it must be used...

in the first line of the constructor body

What is within the body of the constructor of a subclass is no constructor is provided?

True or false: A subclass may redefine a public method as private.

True or false: A subclass may not override static methods of the superclass

Assuming GradStudent and UnderGrad are subclasses of Student, is the following code legal?

Student g = new Student();
Student s = new GradStudent();
Student u = new Undergrade();

Assuming GradStudent and UnderGrad are subclasses of Student, is the following code legal?

GradStudent g = new Student();
Undergrad u = new Student();

What does it mean if a method is polymorphic?

It has been overridden in at least one subclass

Define polymorphism.

The mechanism of selecting the appropriate method of a particular object in a class hierarchy.

Method calls are always determined by the type of the ________ _______, not the type of the object reference.

Making a run-time decision about which instance method to call is known as...

dynamic binding/late binding

The compiler selecting the correct overloaded method at compile time is known as...

static binding/early binding

In polymorphism, what determines the actual method that will be called?

the run-time environment

In polymorphism, the compiler deterimes __ a method can be called, and the run-time environment determines ___ a method can be called

A subclass can call a method in its superclass by using...

If a superclass method calls another method that has been overridden in the subclass, the method that is executed is...

the one in the subclass

Casting a superclass to a subclass type is called a...

Will this code cause an error? Why or why not?

int x = (GradStudent) s.getID();

Yes; dot operator has higher precedence so s.getID() runs before s can be cast to GradStudent

Will this code cause an error? Why or why not?

int x = (GradStudent s).getID();

No, because s is cast to GradStudent before the method is run

Why is a ClassCastException thrown?

to signal an attempt to cast an object to a class of which it is not an instance

Define abstract class.

A superclass that represents an abstract concept, and is not instantiated

An abstract class may contain...

abstract methods

An abstract method only has a...

If a subclass of an abstract class does not provide implementation code for all the abstract methods of its superclass...

it must also be declared as an abstract class

Abstract methods are declared with the keyword...

Abstract methods have no...

True or false: It's impossible for an abstract class to have no abstract methods.

True or false: An abstract class may or may not have constructors.

True or false: No instance can be created for an abstract class.

Define interface.

a collection of related abstract methods

What is the opposite of an abstract class?

a concrete class

A concrete class that implements an interface must do what?

implement every method in the interface

If a class does not implement all the methods in an interface, what must happen?

it must be declared abstract

An interface is declared with the _________ keyword.

Interfaces are implemented using what keyword?

True or false: A class that extends a superclass can also implement an interface.

When a class extends a superclass AND implements an interface, which clause comes first?

the extends clause

True or false: A class can have just one superclass.

True or false: A class can only have one interface.

An (interface/abstract class) typically does NOT provide implementations for any of its methods, while an (interface/abstract class) can.

interface; abstract class

What methods of Object are important to know? (2)

toString; equals

What does the default toString() return?

the class name, an @, and the memory address of the object

Why should you redefine the toString method for all of your classes?

to help in debugging

Do Array objects have a toString method?

How do you print the elements of an array?

traverse the array and explicitly print each element

When will the equals() method return true?

If the objects being compared reference the same memory slot

If you want the equals() method to test the contents of an object rather than its memory location, you must...

override the method

The default implementation of equals() is equivalent to what operator?

What do you use to test objects for equality?

What is a String object defined as?

a sequence of characters

What does a string literal consist of?

zero or more characters, escape sequences, surrounded by double quotes

String objects are immutable. What does this mean?

There are no methods to change them after they've been constructed.

If String objects are immutable, then how do you mutate them?

create a new String

Why are String objects unusual? (think about initialization)

They can be initialized like a primitive type

What is the concatenation operator?

What does the concatenation operator do to two Strings?

combines them into a single String

What does the concatenation operator do with a String and a primitive type?

the primitive type is converted to a String, and the two are combined into one String

How does the compareTo method compare Strings?

according to their position in the ASCII chart, or lexicographical order

What does lexicographical order mean?

the order it comes up in the dictionary

How are characters sorted in the ASCII chart? (out of capitals, lowercase, and digits, in what order do they come?)

digits, capitals, and lowercases

Why shouldn't you use == to test Strings?

it tests whether they're the same reference, not if they're the same string

How do you read the results of a String compareTo method?

If it's less than 0, the String it's called on comes first in the dictionary. If it's greater than 0, the String it's called on comes after. If it's equal to 0, the two Strings are identical.

What does a wrapper class do?

it takes either an existing object or a value of primitive type, "wraps" it in an object, and provides new methods for that type.

Why would you use a wrapper class?

Some methods need the parameters to be objects

What happens when you "wrap" a primitive?

it constructs an object from a single value

What happens when you "unwrap" an object?

it retrieves the primitive value

What is another word for wrapping?

What does compareTo return in the Integer class?

ex: int compareTo(Integer other)

0 if the Integer is equal to other, negative if it's less than other, and positive if it's greater than other

What does the equals method do in the Integer class?

ex: boolean equals(Object obj)

returns true only if the Integer has the same int value as obj.

When you call the equals method in the Integer class, what happens if the object you use isn't an Integer?

it throws a ClassCastException

What does int length() do?

it returns the length of the String

What happens when you use a negative number when calling the String substring method?

an IndexOutOfBoundsException

What does indexOf do?

it returns the index of the first occurrence of the parameter String within the String it's called on

When using indexOf, what happens when the parameter string isn't in the string the method is called on?

the method returns a -1

What does the Double class do?

it wraps a value of type double in an object

What does the Math class do?

it implements standard mathematical functions

What does the method Math.abs(x) do?

it returns the absolute value of x

What does the method Math.pow(base, exp) do?

Returns base^exp.

What four Math methods are necessary to know for the exam?

abs, pow, sqrt, and random

All of the functions and constants in the Math class are...

How do you invoke methods in the Math class?

Math, followed by the dot operator

What is the domain of the result when Math.random() is called?

True or false: Math.random() can return a random real number from 0.0 up to (but NOT including) 1.0.

Provide code to find a random real value in the range [0.0,6.0).

6 * Math.random();

Provide code to find a random real value in the range [2.0,3.0).

Math.random() + 2

Provide code to find a random real value in the range [4.0,6.0).

2 * Math.random() + 4

What is the formula to produce a random real value in the range lowValue<=x<highValue?

(highValue - lowValue) * Math.random() + lowValue;

Provide code to find a random integer in the range [0,99].

(int) (Math.random() * 100)

Provide code to find a random integer in the range [1,100].

(int) (Math.random() * 100) + 1

When did the waterfall model of software development come about?

Name the 5 steps of the waterfall model.

analysis of the specification, program design, implementation, testing & debugging, and maintenance

Define a specification.

a written description of the project

What is the first step in writing a program?

analyze the specification, make sure you understand it, and clarify with the customer if anything is unclear.

Define program design.

a fairly detailed plan for solving the problem outlined in the specification

What should a proper program design include?

all objects that will be used, the data structures that will implement them, and a detailed list of tasks the program will perform

Why is it necessary to select test data?

because not every possible input can be tested

What is test data?

a set of input values to test the program with

When does a compile-time error occur?

during compilation of the program

What happens during a compile-time error?

the compiler cannot translate the program into bytecode and prints an error

What kind of error is a syntax error?

a compile-time error

What causes a syntax error?

violating the rules of the programming language

When does a run-time error occur?

during the execution of the program

When a run-time error occurs, what exactly throws the exception?

the Java run-time environment

What does it mean when an exception is thrown?

execution stops and an error message is printed

What kind of error is an infinite loop?

a run-time error

What is another way to say logic error?

What is a logic error?

when the program compiles and runs but the result is wrong

What are the three characteristics of a robust program?

won't give inaccurate answers for input data, won't crash if the input data is invalid, and won't allow execution to proceed if invalid data is entered

What is program maintenance?

upgrading the code as circumstances change?

When did object-oriented programming become the dominant programming methodology?

What are the five steps in object-oriented program design?

identify classes to be written, identify behaviors, determine relationships between classes, write the interface for each class, and implement the methods.

When designing a program, how do you identify behaviors?

find useful verbs in the program specification

When designing a program, how do you identify class names?

pick out "big-picture" nouns from the program specification

When designing a program, after you identify necessary methods, what do you do?

group the methods into classes

What is encapsulation?

the process of bundling a group of methods and data fields into a class

After encapsulation, what is the next step of designing a program?

decide what data fields each class needs and what data structures should store them

What two kinds of relationships between classes should you consider when designing a program?

inheritance and composition

What is an inheritance relationship?

is-a; involves subclasses and superclasses

What is a composition relationship?

has-a; involves wrapper classes

When implementing classes, what are the two different kinds of development?

bottom-up and top-down

What does it mean when a class is a collaborator?

classes needed to implement a method

If you're using bottom-up development, what is the first thing you need to do?

for each method in a class, list all the other classes needed to implement that method

What does it mean if you use a bottom-up approach?

independent classes are fully implemented and tested before being incorporated into the overall project

What can you use to test a class as you go?

a dummy Tester class

True or false: When writing a class, constructors and methods should be added and tested one at a time.

What is a driver class?

a class that contains a main method that can be used to test the program as you go

What is the purpose of a driver class?

to test the class fully before incorporating it as an object in a completely different class

In what order are classes implemented when using the bottom-up method?

independent classes first, then classes that depend on just one other class, and so on

What is an independent class?

a class whose methods don't need any other class to function

How does a top-down design work?

the programmer starts with an overview of the program, selects the highest-level controlling object and the tasks needed.

If several methods in a class require the same task, you should use...

Define procedural abstraction.

the use of helper methods within a class

Define helper methods.

methods that break up larger methods into smaller tasks

Procedural abstraction is an example of...

top-down development

The process of breaking a long method into a sequence of smaller tasks is sometimes known as...

stepwise refinement

Define information hiding.

declaring instance variables and helper methods as private so client classes can't use them

Define a stub method.

a dummy method that is called by another method being tested

What is an algorithm?

a precise step-by-step procedure that solves a problem or achieves a goal

Define a UML diagram.

a tree-like representation of relationship between classes

What is a precondition?

a statement of what is true immediately before execution of that code

What is a postcondition?

a statement of what is true immediately after execution of that code

An efficient algorithm is one that is economical in the use of... (2)

CPU time and memory

What is an array?

a data structure used to implement a list object, where the elements in the list are of the same type

In Java, an array is an object, therefore what keyword is needed when initializing?

Once an array has been created, its size is...

When an array with doubles or ints is declared, what are the values automatically initialized to?

When an array with boolean values is declared, what are the values automatically initialize to?

When an array with object references is declared, what are the elements automatically initialized to?

Small arrays whose values are known can be declared with a(n)...

initializer list

When getting the length of an array, do you use parentheses? Why or why not?

no, because it's not a method

What should you use to traverse elements in an array?

When passing an array as a parameter, can you modify it? Why or why not?

Yes, because you're passing its object reference and not a copy

Which can grow and shrink as needed in a program: an array or an ArrayList?

In an ArrayList, the last slot is always...

Which only needs a single statement to insert or delete elements: an array or an ArrayList?

What is a container class?

a class or data structure that holds other objects

What three characteristics do all container classes share?

they're designed to be memory and run-time efficient, they provide methods for insertion and removal of items, and they provide for iteration over the entire collection

The ArrayList class implements what interface?

What five methods of List<E> are important to know?

add, size, get, set, and remove

What does the method boolean add(E obj) do?

it appends obj to the end of the list, and always returns true

What does int size() do?

it returns the number of elements in the list

What does E get(int index) do?

returns the element at the specified index in the list

What does E set(int index, E element) do?

it replaces the item at index with the specified element

What does void add(int index, E element) do?

it inserts element at the specified index

What does E remove(int index) do?

it removes and returns the element at the specified index

What does ArrayList() do?

it constructs an empty list

What is a matrix?

a two-dimensional array

In a 2D array, what does arr.length represent?

the number of rows

In a 2D array, what does arr[i].length represent?

the number of columns

What is the format for a for-each loop? (for an array)

for (type [] name : NameOfArray)

When using a for-each loop to traverse an array, what can you NOT do?

replace the value

What are the three methods of traversing a 2D array?

row-column, for-each loop, and row-by-row array processing

What is a recursive method?

A method that calls itself

What happens when a method actually terminates in a recursive loop?

The program returns to the most recent call

What are the two parts of a recursive method?

a base case and a non-base case

What is a base case?

a termination condition that causes the method to end

What is a nonbase case?

actions that move the algorithm towards termination

True or false: A recursive algorithm cannot have more than one base case.

Define tail recursion.

When a method has no pending statements after its recursive call

What is infinite recursion?

when a recursive method has no base case

What error will be thrown if infinite recursion occurs?

StackOverflowError

What happens when there are too many recursive calls?

It can cause memory overflow

When should you use recursion?

When it significantly simplifies the code

Name the two steps of Selection Sorting.

Find the smallest element in the unsorted section of the array, then put that element at the front of the unsorted section.

In selection/insertion sort, for an array of n elements, the array is sorted after how many passes?

How do you do insertion sort?

You move through the array one element at a time, and sort each element as it comes up.

What is the worst case for insertion sort? Why?

If it's already sorted in reverse order; because it will need the maximum number of moves

What is the best case for insertion sort? Why?

If it's already sorted in increasing order, because it will not need to make any moves.

What sorting method is known as a "search-and-swap" algorithm?

In what case will selection and insertion sort be inefficient?

What sorting method is known as a "divide-and-conquer" approach?

What are the four steps in Mergesort?

Break the array in two, mergesort the left half, mergesort the right half, then merge the two subarrays into one.

What is the main disadvantage of mergesort?

It uses a temporary array

True or false: The efficiency of mergesort is unaffected by the initial sorting of the methods.

How does sequential search work?

Each element in an array is compared until the key is found

What is the worst case in sequential search?

if every element needs to be compared

What is the best case in sequential search?

if the key is the first element

What SEARCH method is known as a divide-and-conquer approach?

During binary search, what happens if the 'key' value isn't in the array?

a -1 is returned

Binary search only works if...

the array is sorted

What are the four steps to Binary Search?

Divide the array in half, check to see if the middle value is the key, search the former half, and search the latter half.

What is the best case for Binary Search?

if the key is right in the middle

What is the worst case for Binary Search?

the key is not in the list or is at the end of a sublist

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