Java Lecture2 OVR

8/23/2019 Java Lecture2 OVR

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Java 2

. .

(Statement)

(Expression)


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. .

// , /* */

!

!

()

()

(;)

{ } ()

(;)

. .

, TAB

C /

string String !!!

/

: java.packetname.Classname

: oneword(args), twoWords(args)


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. .

()

: class _

{public static void main(String[] arguments) { }

}

(web browser): public class _extends java.applet.Applet { }

. .

$ _ ,

int x; int x, y, z;

( 0, /0, false, null) int x = 0;

Integer x = new Integer(0); // int x = 0;

Integer x;( x Integer)

x = new Integer(0);( 0)


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. .

- ( !)

boolean true, false

char a, b, ...

byte 8bit (28 )

short 16bit

int 32bit

long 64bit

float 32bit

double 64bit String Blah blah ( new!)

.. Float, Character, Integer

. .

!!! Java :

.. int, float

.. Integer, Float

?

.. System.out.println(Float.MAX_VALUE); - float

.. System.out.println(Float.floatValue()); -

. !


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. .

(.. main)

int x;

System.out.println(x);

!!!

/

. .

typedefC


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. .

/

:

int x[] = new int[];

int[] x = new int[];

/ int x[][] = new int[][];

int[][] x = new int[][];

. .

(new)

int[] x = { 1, 2, 3 }; int[][] x = { { 1, 2, 3 },

{ 4, 5, 6 }{ 7 ,8 } };

, int[][] x = new int[5][6]; int x[0][0] = 1; int x[0][1] = 2; ...

length ..System.out.println(x.length);


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. .

(? - )

int x[] = new int[ ];

int x[][] = new int[ ][];

!

int x[] = new int[ ]; ( !)

int x[k] = new int[k-]; ..

int x[][] = new int[6][];x[0] = new int[1];x[1] = new int[2]; ...

x[0] System.out.println(x[0].length);

. .

class ArrayTest {public static void main (String arguments[]) {

int[] test = new int[3];test[0] = 10;test[1] = 20;test[2] = 30;

System.out.println( = + test[0] + ,

+ test[1] + , +test[2] + = + test.length);}

: = 10, 20, 30 = 3


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. .

T arguments main

Strings ..

public static void main(String[] arguments) { }java _arguments[0] arguments[1] ...

(arguments)

class ArgsTest {

public static void main (String arguments[]) {

System.out.println(arguments[0]);System.out.println(arguments[1]);

System.out.println(arguments[2]);

}

: java ArgsTest first second third

: first

second

third

. .

final : final double PI = 3.14


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. .

final int MAX = 5;

int[] myarray = new int[MAX];

.

. .

(literals)


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. .

(Integers) (Decimal)

10, [0, 9] , .. 1, 2, -50, 400000

(Octals) 8, [0, 7]

.. 0777 (Hexadecimals)

16, [0, 9] , , C, D, E, F .. 0x12, 0xAF

. .

(long)

L l Long .. 5L, 100l, 0xFFL

(float) double

F ffloat

.. 3.2F


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. .

(char)

..

: .. \n, \t, \b, \r, \f (form feed), \\, \, \, \0

(Strings) .. Blah blah \n

. .

:

(..1 ..2)

(.. ..)

(.. ..)

(..1 ..2)


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. .

..1

..2 casting C

.. int float: int x = 5; float y;

y = (float)x;

y = 5F y = x

5

.. float int: int x;

float y = 3.14F; // F doublex = (int)y;

3

. .

.. ..

.. float Float

float x = 5.8F;Float Y = new Float(x);

.. float String float x = 5.8F;

String S = String.valueOf(x);

: new valueOf() String


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. .

..

..

:

.. Float float float x;

Float Y = new Float(3.14);x = Y.floatValue();

3.14

.. Float int int x;

Float Y = new Float(3.14);x = Y.intValue();

3

. .

.. ..

:

.. String floatfloat x = Float.parseFloat(3.14);

class prosthesi{

public static void main(String a[]){

float f1 = Float.parseFloat(a[0]);float f2 = Float.parseFloat(a[1]);System.out.println(f1+f2);

}}

: java prosthesi 2.5 3: 5.5


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. .

..1

..2

.. Float Integer Float = new Float(3.14);

Integer X = new Integer(Y.intValue());

.. String Float Float F = Float.valueOf(3.14)

. .

..1 ..2

casting

Emploee emp = new Emploee();VicePresident veep = new VicePresident();

emp = veep;// cast ()

veep = (VicePresident)emp;// cast ()


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. .

: +, -, /, *, %

: =, +=, -=, /=, *=, %=

.. x = y = z = 4;

/ : ++, --

x++ ++x

: ==, !=, , = y = 5 x = y < 2 x =

false

. .

: :

&& (AND), || (OR)

bit:

& (AND), | (OR), ! (NOT), ^ (XOR),>> (BIN SHIFT RIGHT), 5) && (y > 5) => z = falsez = (x > 5) & (y > 5) => z = false false

z = 4 >> 2 => z = 1 (100 => 001)


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. .

1. [ ], ( ) 10. |

2. ++, --, ! 11. &&

3. new, (cast) 12. ||

4.*, /, % 13. ? : {.. z = (x>y)?2:8 }

5. 14. =, +=, -=, /=, %=, =,|=

6. , =

7. ==, !=8. &

9. ^

. .

java.lang ().

import

: Math.sqrt(4); - sqrt() = Math

Math.cos(230); - cos() = Math

Math.PI; - PI = Math


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. .

:

:String s1 = new String("Dimitris");

String s2 = new String("Dimitris");

System.out.println((s1==s2) + " " + (s1.equals(s2)));

: false true

()String s1 = "Dimitris";String s2 = "Dimitris";

System.out.println((s1==s2) + " " + (s1.equals(s2)));

: true true

. .

(-)

main public static void main(String args[])

Java

Java


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. .

.. 3.14, double. float 3.14F

casting

, java.lang, ..

. .

Math java.lang

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Java Lecture2 OVR