AP Computer Science A Ultimate Guide

Symbol(s) used to add a comment

//

Identifiers

Names that are given to show data that are stored in the memory of a computer when a program is being executed in a computer

Logical error

An error because of the incorrect way a code is structured.

Run-time error

A compiler doesn’t catch this error. It just causes an error with the execution of the program.

Print statement

System.out.print(""); 

Code to assign value to identifier

type identifier = value;

Primitive data

Basic types of data

Integer (int)

It represents any number that is an integer. All positive, negative numbers and zero. Cannot store decimals.

Double

A number that can be positive, negative, or zero, and it can be a fraction or decimal.

Boolean

A value that is either true or false. True = 1, False = 0 in machine code.

Character (char)

It represents a single character that can be represented on a computer. It includes any character that you type on the keyboard. Stored with the use of single quotation marks or an apostrophe.

Modulus operator

% - Returns the remainder once two numbers are divided.

Casting

A process in which data is forced to look like another type of data to the compiler.

Casting double to an int

int x;
double y = 4.5;
x = (int) y;

Casting int to a double

int x = 4;
double y;
y = (double) x;

Increment operator

(++) This increases the value of a number by one.

Decrement operator

(--) This decreases the value of a number by one.

a += b

a = a + b

a -= b

a = a - b

Object

A data type created in Java.

String

An object data type which has a class with many methods that describe the behavior of an object.

Immutable class

Once an object is created, the assigned value cannot change.

Object

data type created in Java

Class

used to build objects

“if” statement

conditional statement that is used in Java to help control the flow of the program

Boolean Operator

==

Logical And

&&

Logical Or

||

Not Equal To

!=

DeMorgan’s Law

to simplify common compound conditions, distribute the ! into the parenthesis and change the && to ||, or vice versa

while loop

loop cycles through again and again, while the condition is considered true

infinite loop

loop that repeats forever because of condition

for loop

statement 1 is executed (one time) before the execution of the code block.

statement 2 defines the condition for executing the code block.

statement 3 is executed (every time) after the code block has been executed.

class

when a group of statements, such as control structures, are all put together to be referred to this

method

group of code that performs specific task

object class

This class houses the “guts” of the methods that the driver class calls.

header

defines method function

constructor

sets object’s initial values for instance variables

instance variables

attributes in a class, also known as fields

precondition

a comment that is intended to inform the user more about the condition of the method and guarantees it to be true.

postcondition

a condition that must always be true just after the execution of a section of code, or after an operation in a formal specification.

aggregate class

Made up of other data, and instances of other classes.

static variable

attribute that is shared among all instances of a class

arrays

a data structure that makes it easier to handle similar types of data

sequential searches

These search through the data one by one in order, and take a long time to execute

binary searches

These search through the data for the desirable value by dividing it into half each time until the desired value is found

sorting algorithms

They take data in an array, and rearrange it into a particular order. They are very powerful because they can accomplish tasks faster, and can make your programs even more efficient.

selection sort

This sort searches and swaps. Once it finds the lowest value, it will swap its position in the array with the data at index 0. The first element is now sorted. The process repeated for index 1. The rest of the array will be searched for the lowest value and is swapped with the data that is found at index 1.

insertion sort

It compares the first 2 elements, and depending on the outcome of this it inserts the second value in front of the first value into index 0, which moves the first value to index 1. The first 2 elements are sorted. Then the third element is checked and this process continues until it’s entirely sorted.

merge sort

This type of sort uses recursion. An array is split into 2 pieces. The piece is sorted. The 2 sorted pieces are merged together into one sorted list. Then in order to sort each of the 2 pieces, the same method is used again until it is fully sorted.

array lists

A huge limitation of arrays is that it has a fixed length, and can only store, one specific type of data.

dynamically sized

used to describe an array list which becomes bigger / smaller as elements are added / removed

2D array

array within an array, like a vending machine

inheritance

A way to create a relationship amongst classes.

inheritance hierarchy

A way to determine how information travels amongst the classes. Ex: The subclasses inherit characteristics of the parent class.

multiple inheritance

when a class has more than 1 superclass, it is defined as ______. not allowed in java

overridden

new version of code takes over old version

polymorphism

When many classes are related to each other by inheritance. Inheritance lets us inherit attributes and methods from another class. uses those methods to perform different tasks.

recursive call

characteristic to call a method itself

base case

Signal the execution to stop the recursion and return to each prior recursive call