Java

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, 2017

50 .

, . - Java.

abstract, assert, boolean, break, byte, case, catch, char, class, const, continue, default, do, double, else, enum, extends, final, finally, float, for, goto, if, implements, import, instanceof, int, interface, long, native, new, package, private, protected, public, return, short, static, strictfp, super, switch, synchronized, this, throw, throws, transient, try, void, volatile, while.

: byte, short, int, long, char, float, double, boolean

, : if, else, switch, case, default, while, do, for, break, continue

: try, catch, finally, throw, throws

: private, protected, public

/ : import, package, class, interface, extends, implements, static, final, void, abstract, native

/ / : new, return, this, super

: synchronized, volatile

: instanceof, enum, assert, transient, strictfp

: const, goto

Java 1.2: strictfp

Java 1.4: assert

Java 5: enum

const goto , .

true, false null . .

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Java - . .

- null . null . null, .

: : byte, short, int, long

: float double

: char

: boolean

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boolean---Boolean

char16'\u0000' 0'\uFFFF' 216-1Char

byte8-128127Byte

short16-215215-1Short

int32-231231-1Integer

long64-263263-1Long

float32-1.4e-453.4e+38Float

double64-4.9e-324 1.8+308Double

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byte 1 . .

short 2 . .

int 4 . 2 , . . byte short int.

long 8 .

( ) , , . , .

float ( ) 32 . , . , 32- .

double 64 . , , . .

char . 16- , Unicode. , 128 ASCII, 256
ISO-Latin-1, , , .

char 0 65535.

, 'A' , "A".

() boolean - true () false ().

, , , , if for.

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: BigInteger BigDecimal . , . , , .

BigInteger: .

BigDecimal: .

( ). : ( ) ( )

:
__ = (_) ;
- (type casting). , , int byte:

int a = 257;byte b = (byte) a;

257 , b byte (256), 1.

byte>short; short>int; char>int; int>long; float>double; byte,short,char>float; int>double; float>double (strictfp) . .

. int double double.

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boolean . . , 0 == false, !0 == true.

:

byte, short, char int

long

float float

double

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Java - NullPointerException.

, - , null. null, . , null, null.

null, .

null

. null, :

Math math = null;System.out.println(math.cos(1));

() , NullPointerException.

, x != null, :x.equals(null) == false;

null. , .

JVM null :aconst_null: null; ifnull ifnonnull: null.
null? ?

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: Byte, Short, Integer, Long, Character, Double, Float Boolean. , .

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- ( ):

Integer i = new Integer(10);Integer i = 10;Integer i = Integer.valueOf("10");

Boolean "true", , true, false.

Number, , , :

byteValue()

doubleValue()

floatValue()

intValue()

longValue()

shortValue()

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"" .

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Integer test = 100;// int i = test//

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Integer itr = null; // int j = itr; // NullPointerException

null , , null -, , , null pointer exception .

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Integer i1 = 200, i2 = Integer.valueOf(200);System.out.println(i1 == i2);// falsei1 = 10; i2 = Integer.valueOf(10);System.out.println(i1 == i2);// trueSystem.out.println(new Integer(10)==new Integer(10));// false

:

[-128; 127]

Integer i=100 Integer i=Integer.valueOf(100);

valueOf(), , . , .

i1 i2 , . Integer, , .

, Java 6 JVM.

Byte, Short, Long , [-128;127].

Byte Short .

Character , [0;127].

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Boolean , , , Byte .

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int

123267890-144

long

12L3267890l-144L

byte, short

:

: 0xFF, 0X32

: 255

: 0377

: 0b11111111, 0B11001 (Java 7+)

Java 7 . .

: 1234_5678__1736

. . 0xFFFFFFFF_F : integer number too large. long.

, :

long l = 100000;

int , , . : incompatible types: possible lossy conversion from int to byte.

:

- double 123.45

D, d double 123.45D

F, f float 123.45F

, hex , , . .

- :

:

1.39e-43f

47e47

POSITIVE_INFINITY = 1.0f / 0.0f;NEGATIVE_INFINITY = -1.0f / 0.0f;NaN = 0.0f / 0.0f;

:

(boolean): true, false

(char)

(String)

null: null

null .

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(Escape-) .

\b (backspace)\u0008

\t (horizontal tab)\u0009

\n (new line)\u000a

\f (form feed)\u000c

\r (carriage return)\u000d

\" (double quote)\u0022

\' (single quote)\u0027

\\ (backslash)\u005c

\uXXXX Unicode\uXXXX

Java 8: Unicode 6.2.0.

U+0000 U+10FFFF.

, U+FFFF - . 16- , U+D800 U+DBFF, U+DC00 U+DFFF.

U+FFFF UTF-16.

Character : 32- .

. '\u000a' '\u000d' : "illegal line end in character literal". '\n' '\r'.

: , . :

"Hello, World!" == "Hello," + " World!"

String. , ( String.intern). , .

new String("Hello, World!") != "Hello, World!"
new String("Hello, World!").intern() == "Hello, World!"

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==

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: [ = ] [, [ = ] ];

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int x = 100double d;

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UTF-16. .

"_" "$" Java . , , , . , .

( ).

int timeToStart = 1000;

class MyVeryUsefulClass { }

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byte b;// b = 17;// int i = 1000 * 256 b;// + MyFirstClass myFirstClass;// MyClass myClass = new MyClass()// +

. MyClass myClass; ( myClass MyClass).

. : 0, 0.0, '\u0000', false, null.

. : variable XXX might not have been initialized.

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md.leonis.first.package.FirstClass.classField

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Java , , .

import java.util.ArrayList

ArrayList . :

import java.util.*

Java . C++, .

(statement) ; . .

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(operator) , . .

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44 :

(assignment)

(arithmetic), (unary)

(equality & relational), (type comparision)

(conditional)

(logical)

(bitwise and bit shift)

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45 . . Java, C++ .

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() (+ab) ;

(a+b) ;

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Java, =, == != . String + +=.

: null NullPointerException.

: ArithmeticException

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=. . , . .

int x = 144;int y = 12 - x;

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x = y = 12;

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Object obj1 = obj2;

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+=, >>>=

obj1

obj2

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int i = (int) 100;// int. long l = i; // int longi = (int) l; //

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boolean. .

boolean b = true, b2 = false;boolean b3 = b & b2;

if, while, do. , .

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if (x == 10 & y++ < 100) z = 256;

& .

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if-else .

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result = x == 0 ? 0 : x / 5;

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Java , 90- .

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