AP CSA Unit 2 Using Objects

Object

a variable of a data type that is user defined

State

data/attributes about that object

behavior

actions that can be performed on the object

class

template for creating an object

object oriented programming

using object type variables in programming

instance variable

Used to store the state, or data of the object instances.

Constructor

signature of a class that allows for the creation of a new object

constructor name

used to create a new object; must match the name of the class and be in lowerCamelCase

instantiate

Create an instance of a class object

parameter list

variables containing values passed to the constructor

new operator

instantiates a new class object

overloading

The process of using the same operator symbol or identifier to refer to many different functions.

formal parameter

parameters that are outlined in the parameter list in the constructor

actual parameter

parameters that are input when a new instance of a class object is created

client

when we use a class that someone else has created, we become a

methods

procedures that allow us to control and define the behavior of an object

null

a keyword that indicates a reference object doesn’t point to any object data

void

indicates that the method doesn't return anything

procedural abstraction

being able to use code that we don't fully understand

return type

determines the type that will be return from a method

access specifier

determines who has access to using the method when writing classes and objects

objectName.method()

Calling a method

return keyword

used to return a value back to the main program from a method

scope

defines which part of the program a variable can be accessed from

Immutable

Unable to be changed or manipulated. Strings are immutable.

Concatenation

The process of adding two String values together. This creates a new String object. Primitives can be concatenated with String objects

Implicit Conversion

The automatic process of transforming a variables data type. This occurs when a primitive and String object are concatenated by changing the primitive value to a String object type.

Escape sequences

Enable users to use special characters and actions within String objects

name.concat(“value”)

returns a new String with “value” appended to the end of name

name.replace(“a”, ”p”)

returns a new String with all instances of “a” in name replaced with “p”

name.toUpperCase()

returns name as Upper Case Letters

\”

Allows for quotations

\\

includes a backlash

\n

creates a line break

\t

adds a tab space

String(String str) constructor

constructs a new String object that represents the same sequence of characters as str

name.length()

returns the number of characters in a String object

name.substring(2, 6)

returns the substring beginning index 2 and ending at index 5

IndexOutOfBoundsException

A String object has index values from 0 to length - 1. Attempting to access indices outside this range will result in this error

name.indexOf(“d”)

Returns the index of the first occurence of d; returns -1 if not found

name.equals(“Karel”)

Returns true if name is equal to Karel; returns false otherwise

name.compareTo(”Karel”)

Returns a value < 0 if name is less than Karel; returns zero if name is equal to Karel; returns a value > 0 if name is greater than Karel

Application Programming Interfaces

APIs and libraries simplify complex programming tasks by providing sets of clearly defined methods of communication among various computing components.

Documentation

reference for how to use different methods and classes

Wrapper classes

class which contains or “wraps” primitive data types as an object

Integer.intValue()

converts Integer value into an int value

Double.doubleValue()

converts Double value into an int value

Autoboxing

converting a primitive value into an object of the corresponding wrapper class

unboxing

converting an object of a wrapper type to its corresponding primitive value

static methods

methods in Java that can be called without creating an object of a class

Math.abs(x)

returns the absolute value of x

Math.pow(base, exponent)

returns the value of base raised to the power of exponent

Math.sqrt(x)

returns the positive square root of x

Math.random()

returns a double value greater than or equal to 0.0 and less than 1.0