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