AP Computer Science A

accessor method

a method that accesses an object but does not change it

actual parameter - the expression supplied for a formal parameter of a method by the caller

address

a location in memory at which a binary number (usually a byte, or value of 8 bits) is stored. The location in memory can itself be identified by a binary number - this number, the absolute or explicit address, gives the absolute location of the address in memory, while a relative address specifies a location memory (some other address only in relation to the current, or base, address. All access to memory is access to to a cell of memory found at a specified address.

algorithm

a well-ordered collection of unambiguous and effectively computable operations that, when executed, produces a result and halts in a finite amount of time

[[an unambiguous, executable, and terminating specification of a way to solve a problem

argument

an actual parameter in a method call, or one of the values combined by an operator]]

arithmetic/Logic Unit (ALU)

ASCII

The American Standard Code for Information Exchange - a character-encoding scheme based on the English alphabet used to represent text in computers. It uses 8 bits to represent each character, so it is able to encode a total of 2^8 = 256 different characters. These are assigned the integer values 0 to 255. Only 32 to 126 have been assigned to printable characters. The ASCII has been largely supplanted by UNICODE and the UCS (universal character set), which are backwards compatible with it (commonly encoded using UTF-8, UTF-16, and UTF-32 representing character sets using 8, 16, and 32 bits respectively. UTF-16 can represent 65,536 characters.)

binary

the binary, or the base-2, positional numbering system represents numerical values using only two symbols, 0 and 1

bit

a contraction of binary digit; the smallest unit of information, having two possible values: 0 and 1. A data element consisting of n bits has 2ⁿ possible

boolean

a data type with two possible value representing true and false.

boolean expression

an expression in a programming language that produces a boolean value when evaluated, i.e., true or false

boolean operator

an operator that can be applied to Boolean values. Java has 3 boolean, or logical, operators: &&, ||, and !.

byte

a number made up of 8 bits. Essentially, all currently manufactured computers use a byte as the smallest unit of storage in memory

cache memory

a special, super-high-speed memory unit. Operating on the principle of locality, which says that when the computer uses something it will probably use it again very soon, when the computer references a piece of data for the first time, it stores that data in cache memory, and when it needs to fetch a piece of information, it first looks in cache memory before performing a memory fetch. Since accessing cache memory is so much faster (typically 5 to 10 times faster) than accessing RAM, it is still faster to access cache memory first and then look in RAM if the data is not found (the cache hit rate tells us just how much faster).

cast

Explicitly converting a value from one type to a different type

class

a programmer defined data type, may be a blueprint or template for creating an object

computer

the study of algorithms, including their formal and mathematical properties, their hardware realizations, their linguistic realizations, and their applications

constructor

A set of statements for initializing a newly instantiated variable

control unit

Unit within the computer that actually carries out the operations of a program. the control unit does three things: fetches from memory the next instruction to be executed, decodes it, and executes it by issuing the appropriate command to the ALU, memory, or I/O controllers. It halts when the last instruction in the program is reached.

encapsulation

The hiding of implementation details

explicit parameter

A parameter of a method other than the object on which the method is invoked

flops

floating-point operations per second

formal parameter

a variable in a method definition; it is initialized with an actual parameter value when the method is called

gigabyte

1 billion bytes. In binary, technically 2^30 bytes, or 1 073 741 824 bytes

I/0 buffer

memory stored in the I/O controller for transfer between RAM and an I/O device (such as characters from memory to a screen, or from a mass storage device to memory).

I/O controller

a device that handles the details of input/output and compensates for any speed differences between I/O devices and other parts of the computer. Contains a small amount of memory, called an I/O buffer, and enough I/O control and logic processing capability to handle the mechanical functions of the I/O device, such as the read-write head, paper feed mechanism, and screen display. It is also able to transmit to the processor a special hardware signal, called an interrupt signal, when an I/O operation is done.

IDE

Integrated development environment, such as Eclipse:

A software application that provides comprehensive facilities to computer programmers for software development. An IDE normally consists of:

- a source code editor

- a compiler and/or an interpreter

- build automation tools

- a debugger

implicit parameter

The object on which a method is invoked. For example, in g.play(), the object g is the implicit parameter of the method play.

initialize

to set a variable to a well-defined value when it is created. int x = 0; initializes the variable x with a value of 0.

instance

(of a class, an object whose type is that class)

instance variable

a variable defined in a class for which every object of the class has its own value.

instantiation

construction of an object of a given class

instruction set

All of the machine-language commands that a particular CPU is designed to understand.

kilobyte

1000 bytes, technically 2^10, or 1024 bytes in binary

local variable

a variable whose scope is a block (it can only be accessed within that block)

logic gate

A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device.

loop

a sequence of instructions that is executed repeatedly

machine language

instructions that can be executed directly by the CPU

mass storage

nonvolatile means of storing information. There are two distinct forms: direct access storage devices (DASDs) and sequential access storage devices (SASDs). These devices can store a great deal of memory and, because they are nonvolatile, do not require a power source in order to persist. They are used for archival storage, and for storage of information that is not needed immediately by the computer.

megabyte

a million bytes, technically 2^20, or 1 048 576 bytes

memory

the fundamental unit of a computer that stores and retrieves the instructions and the data being executed.

Random access memory has the following 3 characteristics:

1. Memory is divided into fixed-size units called cells, and each cell is associated with a unique identifier called an address. These addresses are the unsigned integers 0, 1, 2, ... , MAX.

2. All accesses to memory are to a specified address, and we must always fetch or store a complete cell - that is, all the bits in that cell. The cell is the minimum unit of access.

The time it takes to fetch or store the contents of a cell is the same for all the cells in memory.

memory registers

the two registers used to implement the fetch and store operations. Fetch and store operations require two operands, the address of the cell being accessed and either the value being stored by the store operation or the value returned by the fetch operation.

Memory Address Register (MAR)

holds the address of the cell to be fetched or stored. Because the MAR must be capable of holding any address, it must be at least N bits wide, where 2^N is the address space of the computer.

Memory Data Register (MDR)

contains the data value being fetched or stored. Typically a multiple of 8 bits, since it it is used to hold the data to be fetched or stored and all data must be stored in cells that are 8 bits wide.

method

a sequence of statements that has a name, may have formal parameters, and may return a value. A method can be invoked any number of times, with different values for its parameters.

method signature - the name of a method and the type of its parameters

mutator method

a method that changes the state of its objects, as opposed to an accessor method

object

a value of a class type

object reference

a value that denotes the location of an object in memory. In Java, a variable whose type is a class contains a reference to an object of this class.

object-oriented programming

designing a program by discovering objects, their properties, and their relationships

parameter

an item of information that is specified to a method when the method is called. For example, in the call System.out.println("Hello, World!"), the parameters are the implicit parameter System.out and the explicit parameter "Hello, World!".

parameter passing

specifying expressions to be actual parameter values for a method when it is called.

primitive data type

a data type structured by Java to hold a single data item (Integer, character, floating point, true/false, long)

pseudocode

a high-level description of the actions of a program or algorithm, using a mixture of English and informal programming language syntax

Random Access Memory

RAM, electronic circuits in a computer that can store code and data of running programs. random access is the ability to access any value directly without having to read the values preceding it.

register

a storage cell that holds the operands of an arithmetic operation and that, when the operation is complete, holds its results.

scope

the part of a program in which a variable is defined

software

(computer science) written programs or procedures or rules and associated documentation pertaining to the operation of a computer system and that are stored in read/write memory

stored program concept

central characteristic of Von Neumann Architecture and the design of all modern computers, in which the instructions to be executed by the computer are represented as binary values and stored in memory

syntax

rules that define how to form instructions in a particular programming language

terabyte

1 trillion bytes - in binary actually 1099511627776, or 2^40 bytes

transistor

the elementary building block of all modern computers. A solid-state device with no moving parts that can be in either an on or off state. Transistors, along with electrical conducting paths to them, are printed photographically on a wafer of silicon to produce an integrated circuit, or chip (currently about 1 billion transistors can be printed in a space of 1 sq cm)

truth table

a mathematical table used to compute the functional values of logical expressions on each possible combination of their logical variables. Often the variables used are 0s and 1s but they may be Ts and Fs as well

Von Neumann architecture

Theoretical model for nearly all modern computers. Such computers are composed of four major subsystems (memory, input/output, the ALU or arithmetic/logic unit, and the control unit), the stored program concept (in which the instructions to be executed by the computer are represented as binary values and stored in memory), and the sequential execution of instructions (in which one instruction at a time is fetched from memory and passed to the control unit, where it is decoded and executed).

white space

any sequence of only space, tab, and newline characters