Parts of a Java Program

byte

1 byte ranges -128+127

short

2 bytes -32,768 to 32,767

float

4 bytes +- 3.4 * 10^38 with 7 digits of accuracy

int

4 bytes ranges 2,147,483,648 to 2,147,483,647

double

8 bytes +- 1.7 * 10 ^-308 with 15 digits of accuracy

long

8 bytes -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807

Scope

A variable's scope is the part of the program that has access to the variable. - the scope of a variable is the part of the proggram where the variable may be accessed by its name.

final

Java key word that keeps a declared variable constant and doesnt allow changes during the runtime of the program.

class "public class Simple"

Java key word. -indicates the beginning of a class definition -one of the uses is to serve as a container for an application

what can be used to read inputs from a keyboard

Scanner class. it provides methods that you can use to retrieve the input formatted as primitive values or strings.

Scanner keyboard = new Scanner(System.in);

Scanner keyboard - declares a variable named keyboard. the data type of the variable is Scanner. because Scanner is a class the keyboard variable is a class type variable (class type variables hold the memory address of an object) therefore the keyboard variable will be used to hold the address of a Scanner object. = new Scanner (System.in) -(=) assigns something to the keyboard variable. - new is a java key word to create an object in memory - Scanner (System.in) the type of object to be created, this specifies that a scanner object should be created and it should be connected to the System.in object the memory address of the object is assigned (by =) to the variable keyboard. after the statement executes the keyboard variable will reference the Scanner object that was created in memory

what is the class provided by Java API for handling strings

String class. first step in using the String class is to declare a variable of the String class data type i.e String name it has numerous methods

Math.sqrt Method

System.out.println(Math.sqrt(25.0) the method will return the squar root of 25.o which is assigned to the result variable

what's a flag

a boolean variable that signals when some condition exists in the program. when the flag variable is set to false it indicates the condition does not yet exist. if set to true it means the condition does not exist.

classes and objects

a class can be seen as a blueprint from where an object can be made from. so a class is a description of an object not one itself.

JOptionPane

a class that allows you to display a dialog box. or requests inut.

System

a class that is part of the Java API. contains objects and methods that perform system-level operations one object contained in the system class is named out.

showMessageDialog

a dialog box that displays a message; an OK button is also displayed

showInputDialog

a dialog box that prompts the user for input and provides a text field where input is typed : an OK button and a cancel button are also displayed

whats a method

a group of one or more programming statements that collectively has a name.

Public

a java key word. known as an access specifier, it controls where the class may be accesessed from. the public specifier means access to the class is unrestricted

Variables

a named storage location in the computer's memory.

unicode

a set of numbers that are used for representing characters

the char Data type

a variable of the char data type holds one variable at a time i.e. "a"

the String class

allows you to create objects for holding strings. also has methods that allow you to work with the strings -a string is a sequence of characters

objects

an objects attributes are data values that are stored in the object. an objects methods are procedures that perform operations on the object's attributes. the programmer designs the object by determining the attributes and methods and then creates a class that describes the object.

Math.PI

another named constant. it is assigned the pi value (3.24) area = Math.PI * radius * radius

API

application programmer interface. this is a library of prewritten classes for performing specific operations. the print and println methods

class names

capitalize the first letter of a class name, as well as the first letter of each subsequent word it contains. ClassTodayIsFun

if statement

causes one or more stataements to be true when a boolean expression is true. use decision structures. dont require ; in its statements

boolean data type

data type for holding one of two variables true or false.

relational operator

determines whether a specific relationship exists between two values example the > < =

floating point data types

double and float. these are used to get decimal or fractional values

when do you use a block of statements

during if statements..

instance

each object that is created from the string class is called an instance from the class, since class type variables don't hold the value but create an object to hold the storage to the value of the literal

what is required to use the JOptionPane class

import javax.swing.JOptionPane;

simple

is the name of the class. this name is made by programmer the name of the class must be the name of the file as well. i.e. Simple.java

final

java key word that makes a variable a constant. and prevents it from changing through out the duration of the program. final double INTEREST_RATE = 0.069;

identifier

made by programmer to represent some element of a program. variable names and class names are identifiers

length method

part of the string class. it returns the length of the string stored in an object.

Primitive type variablesvs class type variables

primitive variables hold the actual data items for example number = 25; this stores 25 in the variable a class type variable holds the memory address of the data item it is associated with.

print println \n

print continues the message on the same line println goes to the next line before starting the message so does \n

System.in

refers to the standard input device (keyboard).

System.exit(0);

required as the last statement in the method if you use the JOptionPane class.

Math.pow Method

result = Math.pow( 4.0, 2.0) result = 4^2

string literal, and integer literal

string literal "today is a great day" integer literal " 6 "

the Math Class

the Java API provides a class named Math, this contains numerous methods that are useful for performing complex math operations

charAt (index)

the argument index is an int value and specifies a character position in the string. first character at 0 next at 1... char letter; string name = "Herman"; letter = name.charAt(3) after this code executes the variable letter will be 'm'

string literals

the group of characters inside the quotation marks. at the end has a ; which means it is finished literals can also be used for variables aswell

main

the name of the method. this is the starting point of an application. every java program must have a main method

out

the out object contains methods such as print and println for performing output on a system.

name = "Joe Mahoney''

the string literal causes a String object to be created in memory with the value "Joe Mahoney" stored in it. then the assignment operator stores the address of that object in thename variable. after this statement executes the name variable references a String object.

public static void main(String[] args)

this is a method header. it marks the beginning of a method

int value ;

this is a variable declaration. this says the variables name is value and int says it must hold an integer. it also ends with a semicolon

toLowerCase()

this method returns a new string that is lowercase equivalent of the string contained in the calling object String bigName = "HERMAN"; String littlName = bigName.toLowerCase(); after this code executes the object referenced by littleName will hold the string "herman"

float number ; number = 33.4;

this will not work float number ; number = 33.4F; this will work

concatenation

using the + operator in a string

local variables

variables declared inside a method cant be accessed by code that is outside the method, or inside the method but before the variable's declaration