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INPUT
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To use Scanner, import Scanner library:
import java.Object.Scanner |
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Scanner scan = new Scanner(System.in);
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name = scan.nextInt();
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name = scan.nextLine();
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name = scan.nextDouble();
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OUTPUT
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System.out.print ( "Hello" );
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System.out.println ( "Hello" ); // New line.
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COMMENTS
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// A single line comment.
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/*
* Multiple * line comments. */ |
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package-info.java //Need to generate.
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/**
* Javadoc comments generate a HTML file. * @author * @version */ |
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PRIMITIVE DATA TYPES
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int value = null; //Doesn't compile.
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byte
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8 bits
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short
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16 bits
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int
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32 bits
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long
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64 bits
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char
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Textual: (16 bits)
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boolean
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Logical: true/false
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float (decimal)
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Floats 15 places (32 bits)
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double (decimal)
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Floats 15 places (64 bits)
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FINAL VARIABLES
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Permanent Values
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final double PI = 3.14159265;
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final String LANGUAGE = "Java";
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abstract
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final/ly
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public
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assert
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float
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requires
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boolean
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for
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return
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break
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goto
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short
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byte
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if
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static
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case
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implements
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strictfp
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catch
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import
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super
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char
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instanceof
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switch
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class
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int
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synchronized
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continue
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interface
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this
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const
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long
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throw/s
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default
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module
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transient
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do
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native
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true
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double
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new
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try
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else
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null
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var
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enum
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package
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void
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exports
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private
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volatile
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extends
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protected
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while
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false
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||
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REFERENCE DATA TYPE
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String name = Always within quotes;
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String words = "123 have no value";
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STRING CONCATENATION
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System.out.println("Hello " + variable + "." );
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System.out.print (variable + " Hello World");
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CONCATENATION RULES
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number + number = number
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number + String = number + String
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String + number = String
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Above number changed to a String!
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String + (number) = String + number
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Use ( ) to override String change.
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COMPOUND ASSIGNMENT OPERATORS
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Syntax to assign arithmetic operation result back-into "assignment" variable.
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+=
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Add values
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-=
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Minus values
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*=
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Multiply values
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/=
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Divide values
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%=
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Modulus (remainder)
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++
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Adds one
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--
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Subtracts one
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x = x + 1;
x += 1; x++; |
//adds one to x
//adds one to x //adds one to x |
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MODULAR DIVISION (%)
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REMAINDER
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Only works on integers!
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7 % 2 =remainder 1
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8 % 3 =remainder 2
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Find even numbers
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x % 2 = remainder 0
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Find odd numbers
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x % 2 = remainder 1
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Integer.MIN_VALUE Integer.MAX_VALUE
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2147483647 -2147483648
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Package
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java, lang, shapes, etc...
package.name, java.io, etc... com.example.mypackage, etc... Lowercase letters. Separate words with dots (.) Companies: "reversed Internet domain" starts their package name. |
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Class
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Color, Button, Cats, etc...
CambridgeCitySchools, etc... NOUNS: Each word starts with an uppercase letter.No acronyms. |
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Method
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main(), print(), equals(), etc...
newMethod(), toString() etc... VERB: First word lowercase. Adding words: First letter uppercase. |
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Variable
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area, name, size, etc...
newTriangle, rightSide, etc... IDENTIFIER: first word lowercase. Adding words; first letter uppercase. No keywords. No special characters to start. Avoid one letter: x, y, z, etc. |
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Final Constant
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PI, BLUE, MATH, etc...
MAX_PRIORITY, CITY_ZIP, etc... All uppercase letters: Every word separated with an underscore(_). |
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(double) 1/3 = 0.3333
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Results a double
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int value = (int) 4.7
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Narrowing Cast
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(int) 3.86 = 3
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Truncated
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WIDENING & NARROWING CASTING
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Does not round: Truncates!
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byte→short→char→int→long→float→double
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Narrowing Casting ( manually )
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larger smaller
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Widening Casting ( automatic )
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smaller larger
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ROUNDING
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int nearestInt = (int) (number + 0.5)
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int nearestNegInt = (int) (negNumber – 0.5)
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