CSA - Unit 2

• Something being created/ manipulated by the program

• Characterized by it’s state and behavior

• Instance of a class

• A variable that represents an object

• Encapsulates data

• An object is an instance of a class

• Usable by all client programs (pieces of code outside the class)

  • All classes are public in AP Java subset

• Accessible to all client programs

• Can only be accessed by methods in the same class

• Memory allocation only happens once

  • Shared by ALL INSTANCES of the class

• Cannot be changed

• Public

• Single value that applies to the whole class instead of a new instance for each object of the class

  • BankAccount.PENALTY for client

  • PENALTY in own class

Public void Withdraw (String password, double amount)

Access Specifier | Return Type | Method Name | Parameter List

• Access specifier = who has access

• Void = method doesn’t return a value

  • Parameters are separated by commas, require data type

• Implementation follows header and is enclosed by {}

• Method that creates an object of the class

  • Name is same as class, no return type

• No parameters

  • Provides initial values for an object

• Variable assigned values of the object

• Sets instance variables to values of those parameters

  • They can be changed in different references

• Public method that accesses a class object without altering it

  • .getBalance

• Changes state of an object by modifying at least one instance variable

• Perform operations on individual objects of a class

• Constructors, accessors, mutators

• Perform an operation for the entire class

• Keyword Static in header

  • Can use a static variable in its code

• Main() method is always static

  • Tests other classes

• 2 or more methods in the same class with the same name but different parameter lists

• Distinguished by method SIGNATURE

  • Can’t have 2 methods with same signature but different return types, so return type is irrelevant

• Region in which the variable/ method is visible and can be accessed

• A class’s instance + static variables and methods belong to the class’s scope (enclosed by {})

  • DOT OPERATOR NOT NEEDED

• Defined inside a method or statement

  • Scope is from declaration to end of its block

• Precedence over instance variables with same name

• Piece of code enclosed by {}

• Instance methods are called for a particular object, which is an IMPLICIT PARAMETER for the method

  • Referred to with keyword this

• Objects and arrays

• String, Random, int[], string [] [], Cat, etc

• STORES MEMORY ADDRESSES

  • If object is changed, any references aliased to it will also change

• Double, int, char, boolean

  • STORES VALUE DIRECTLY

• Uninitialized object variable

• Null pointer

• Doesn’t refer to an object

• Placeholders for actual parameters

• String acctPassword, Double amount

• Actual values given to a method call

• Match up with formal parameters

• Changes made to parameters of method will not affect the values of the arguments in the calling program

• Basically goes back to what it was before

• Passed by value