. , . , Java , Java Object, .
Java , . (class wrappers). , , , . - int char, Integer Character.
byte | Byte |
short | Short |
char | Character |
int | Integer |
long | Long |
float | Float |
double | Double |
! Character , char .
, . ( - box) (boxing), (unboxing). ( ) , Value(). , byteValue() Byte. , , . , , .
, :
Integer obj1=10;
int i1= obj1*2;
Byte b=1;
obj1=i1/10;
b=2;
, - , . . , - ( JDK) . , , .
. , , :
Byte.MIN_VALUE, Byte.MAX_VALUE, Float.MIN_VALUE, Float.MAX_VALUE, Double.MIN_VALUE, Double.MAX_VALUE ..
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, , . , ,
Byte.parseByte()
Short.parseShort()
Integer.parseInt()
Long.parseLong()
Float.parseFloat()
Double.parseDouble()
.
Byte.valueOf()
Short.valueOf()
Integer.valueOf()
Long.valueOf ()
Float.valueOf ()
Double.valueOf ()
, , .
:
int n1=Integer.MAX_VALUE;
double d1= Double.MIN_VALUE;
,
double d2= Double.parseDouble(jTextField1.getText());
,
double d2= Double.valueOf(jTextField1.getText());
, valueOf Double. double, , d2 . , . , , , ( ). , . : , .
. , , : , , . , ,
a*b/c+d
,
((a*b)/c)+d
, , . , .
(a+b)*c : a+b, c.
Java , . , : , . , , . , , .
. , .
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- | ||||||
() | [ ] | . | ||||
++ ++ | -- -- | ~ | ! | + - | ||
new | () | |||||
- | * | / | % | |||
+ | - | |||||
>> | >>> | << | ||||
> | >= | < | <= | instanceof | ||
== | != | |||||
& | ||||||
^ | ||||||
| | ||||||
&& | ||||||
|| | ||||||
?: | ||||||
= | =(+=, -=, *=, /= ..) |
- (enum)
, , , . , . . - enum ( enumeration ), , . ( 1.2).
- , - . - . , . -:
.
, - . 0, 1, . ordinal(), . compareTo, - .
name(). valueOf, .
, values() , . : .values()
- Monthes () Spring (), :
enum Monthes {jan,feb,mar,apr,may,jun,jul,aug,sept,oct,nov,dec};
enum Spring { march, apr, may };
, , , . - Monthes Spring , .
, , , :
public Monthes m1,m2=Monthes.mar, m3;
- m1, m2 m3,
Spring spr1=Spring.apr, spr2;
- spr1 .
:
spr2=spr1;
spr1=Spring.may;
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System.out.println(" ="+spr2.compareTo(Spring.march));
=1,
spr2 Spring.apr, 1 , Spring.march, .
spr2 Spring.may. , , spr2.ordinal(). 2, may ( 1 - , ).
, spr2, spr2.name(). may - .
, null.
System.out.println("spr2="+spr2);
spr2
spr2=null
spr2.ordinal() spr2.name() ( )
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
Spring , i, :
spr1=Spring.values()[i];
Spring :
spr1=Spring.valueOf("march");
3
ü boolean true false.
ü && -Ȕ, || - Ȕ, ^ - Ȕ,! Ŕ . Java .
ü a b , a b, . , ==.
ü Java byte, short, int, long char, . char , .
ü long, int, L.
ü . , public final.
ü Java float double (, ).
ü , (Math.PI) (Math.E) Math, java.lang.
ü int long. byte, short char int, . long, long, .
ü Java float double. double, float, double, float double.
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ü , , , .
ü Java , . (class wrappers). , , , . int char, Integer Character.
ü , . ( - box) (boxing), (unboxing). .
ü . , , : Integer.MIN_VALUE, Integer.MAX_VALUE, Float.MIN_VALUE, Float.MAX_VALUE, Double.MIN_VALUE, Double.MAX_VALUE. ..
ü Java 15 . , , .
ü , , , . , . .
:
- , a==b a=b. : if(a==b){...} if(a=b){...}. Java , . a b if(a=b){...} , a b, . , , .
- , BASIC, a ^ b , ab. Java Math.pow(a,b).
- , C/C++, a & b a | b ( ) . Java ( ) , & | Ȕ Ȕ.
- instanceof instanceOf.
- java.lang.Math java.math.
- , , byte, short char int, . , , , int.
- , , .
- , .
- . . .
- . , , , , sin. , , . double. sin , .
- . , JButton . , . , .
:
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if(jRadioButton1.isSelected())
1;
if(jRadioButton2.isSelected())
2;
if(jRadioButton3.isSelected())
3;
- Java . Spring (), , m2=m1 m2. Spring m1 m2. m1 , April, m2 . m2=m1 m2 m1. m2 m2.