test review

variable

has a data type, identifier and a value.

Data Type

how much storage needed for variable

what things it can do

methods that can be executed w the object

creating variable

must declare before use, declare ONCE

dataType variableName

primitive data types

not object, methods can’t work on them, arithmetic operations, contain actual value

int - whole number 4 bytes

double - real numbers, no modulus, 8 bytes

objects

entities in your program that you manipulate by calling methods of that class.

Objects belong to a class; any data type representing an object will start with a capital letter

primitive data types - lowercase

The amount of storage for the object varies so the Variable name points to an address, not the actual data.

The address it points to will be the starting location of the actual data. So it is said to store a reference to the data.

String

a special type of object. Some things are done for you, so you can treat this data type like a primitive data type in many cases.

String variables will point to an address of where the data is located.

String variables can be printed just like a primitive variable, it will print the actual value because of special handling already done for us by Java (even though it contains an address.)

The String data is immutable – meaning there are no methods of the String class that actually CHANGE the value stored.

If you assign a new value to the variable, it will store the address of the new data instead of the address of the original data.

The original data will go away if no variable name is pointing to it.

initializating

assignment goes right to left

age = 16, 16 is assigned to age

declaration and initialization

dataType VariableName = value; ex: int age = 16;

identifier naming rules

1) can only use characters, numbers, underscore “_” and dollar sign”$”

2) cannot start with a number

3) cannot use blanks

4) cannot use any other special symbols such as “,” “/” or “&”

5) cannot use reserved keywords OR identifiers already declared in the program

case sensitive

class - Uppercase

variable and method - lowerCase

identifier types

a. reserved – part of Java language. Ex: public, void, static

b. pre-defined in libraries – ex – method names like println

c. user defined – created by the programmer

class method object

class = blueprint, layout, workspace for an object - something you can manipulate with methods

data = variables

actions = methods

“new” operator from another class to create an object of the class

class won’t create an object, only controls and provides address

class defining object - no main method

class Method

sequence of instructions that accesses the data of an object.

defines behaviors of an object

calling a method - all method names followed by parentheses - distinguished method (holds verb) and variable identifier (holds noun)

what is Printstream

class

out is a pre-defined object of that class created in the System class.

print and println are methods of the PrintStream class.

what is String

String is a class for an object that contains a set of characters.

methods for String class

length – returns the number of characters including special symbols and blanks that are contained in the string object passed as the implicit parameter.

toUpperCase – returns a copy of the implicit parameter converted to have only upper case characters.

toLowerCase - returns a copy of the implicit parameter converted to have only lower case characters.

replace method carries out a search-and-replace operation. It constructs a new string that is obtained by replacing all occurrences of the first explicit parameter with the second explicit parameter.

NOOO mutator methods everything here is a new copy!!

when u want to create an object…

use the Constructor method

Constructor’s job is to instantiate the object – declare and initialize and return the reference (address) of the new object.

special methods w/ own set of rules

To call a constructor, you use the new operator followed by a class name and parameters. as follows:

new Rectangle(5, 10, 20, 30);

When you call a constructor (by using the new operator) you are “instantiating” or “constructing” the object. Unlike other methods, Since there is no object yet, you do not use the object name as an implicit operator.

The instantiation of an object returns the ADDRESS of the object it created. Bank tom = new Bank();

Bank = class, tom = reference name / identifier, Bank() = calls instructor

method name is overloaded when

class has more than one method with the same name (but different parameter types).

creating multiple methods with the exact same name, but different inputs (parameters).

method signature

method name(data type, data type)

parameter = input, what r the types?

Implicit parameter – the object on which the method is invoked

ex: greeting.length() greeting is the implicit parameter to the method length.

Explicit parameter – additional information needed for the method to work. The explicit parameter is passed in a set of parenthesis FOLLOWING the method name.

Example System.out.println(“This is my explicit parameter”); Some methods require multiple explicit parameters, others don't require any.

return values

just printing the answer displays it

returning the value is useful when you calculate a piece of data and give it back to the rest of the program so you can still use it

void - no value returned; compiler error if attempted to print

accessor

returns the state of the object – one specific value such as the color or location of a bug. Usually has no explicit parameters. The return type is listed in the method header and must be the data type of the data being returned.

mutator

modifies the state of the object. ex: A withdrawal from a bank account object.

Usually requires an explicit parameter to contain the new value or the amount to adjust the current state. Usually has a return type of void indicating no data is returned.

test programs

have a main method and call the methods of a class that contains objects.

Classes that control the behavior of an object will not have a main method.

java classes are grouped into…

packages

use import statement to use classes defined in other packages

formal parameter

inside the parentheses of a method - DATA TYPE, not actual value

Which operator is responsible for getting the space needed for an instance of an object?

new

two things every object has

attributes and methods

attributes and behaviors

data and methods

data and behaviors