Computer Science A Unit 3

Unit 2 Us objects Strings and class types Escape Sequences and String Concatenation String Methods Classes and Objects Using Constructors Using Methods Math Functions

Primitive data types

Primitive data types

Hold only one piece of data at a time

Boolean, int, double

stored as an actual value

Reference data type (class)

hold more than one piece of data type

Int, double, String, Scanner

have built-in tools - tools which you can use to work with an manipulate data

memory address that points to the place where info is stored (don’t site the actual value)

Strings are immutable

means you cannot change Strings without moving to a new memory location. Java will do this automatically.

null

Placeholder that means no reference

Order of operations

Rules that tell us the sequence in which the code is run

String memory

Each character of a String is stored individually

Each character is given an address that starts at 0

index

The address number of each character

.length() method

Tells us the length of the String

.equals() method

Tests if 2 strings are equal - If the same contents of both Strings heave the same characters in the same places

Will return the true or false (Boolean)

.substring(start, stop) method

Creates a subset of characters from the starting index up to but not including the stopping index

.substring (start)

Returns the subset of characters from the start to the end of the String

.toUpperCase() method

Returns the String changed to the uppercase letters

.toLowerCase()

Returns the string changed to the lowercase letters

.compareTo() method

Lets us compare 2 Strings alphabetically

.indexOf() method

Method that allows you to search through a String to find a particular character

Returns the index position as an int

Object

Specific instance of a class with defined attributes

Instance variables

Define true attributed for objects

Attributes

Store and represent data associated with objects whose behaviors are defined by the methods

Instance

Specific object that is created from the class

Constructing

The process of creating a new object

Constructor

Special method that creates a new object

Every class defines its own constructor

Doesn’t have a return type in Java

Parameter

Information we put in () and determines how we construct our new object

API

Application Programming Interface

It’s the way programmers share information or code with each other

State

Attributes of the object and their values (at a given time) that define what our object (ex: rectangle) looks like

setRadius() method

Characteristics of a circle: round, radius, diameter, circumference, pi

True for the Circe class

Void methods

Performs an action, but doesn’t return any information

Generally changes the state of an object

Non-void methods

Changes the state of an object and returns a value to us

Mostly used for pulling information for an object

Method overloading

By quantity (number of parameters)

By data type

By different order

Method Signature

Made up of methods name, number of parameters, and the data type of those parameters

Java determines which method to call based on parameter number and number and data types - the method signature

Signatures can only have the same name - those are overloaded methods - but they have to be different parameters

Wrapper class

Wraps a primitive data type into objects/class so we can apply methods to them

CompareTo() method

Compare 1 integer to another integer

Compares 1 double to another double

Autoboxing

Automatic conversion between primitive data types and their corresponding object wrapper classes

Unboxing

When java is given an Integer and expects an int, it automatically converts, or unboxes, the integer into a primitive int.

Math Class

Part of Java.lang package

We need to make sure it is imported to our program

Math.abs() method

Performs an absolute value calculation

int the as an input→ int as an output

double used → double returned

.pow(x,y) method

Performs exponent math

Accepts 2 parameters: the base and the exponent

Performs a calculation: base (x) raised to the exponent power (y)

.sqrt() method

Calculates the square root of the double we send it

Returns a double

math.random()

Returns a double from 0.0 to but not including 1.0

non-static methods

Specify the object, then the method to perform on the object

Static methods

Performed just by referencing the Class name