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8/23/2019 Java Lecture2 OVR
1/18
1
Java 2
. .
(Statement)
(Expression)
8/23/2019 Java Lecture2 OVR
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2
. .
// , /* */
!
!
()
()
(;)
{ } ()
(;)
. .
, TAB
C /
string String !!!
/
: java.packetname.Classname
: oneword(args), twoWords(args)
8/23/2019 Java Lecture2 OVR
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3
. .
()
: 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)
8/23/2019 Java Lecture2 OVR
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4
. .
- ( !)
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()); -
. !
8/23/2019 Java Lecture2 OVR
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. .
(.. main)
int x;
System.out.println(x);
!!!
/
. .
typedefC
8/23/2019 Java Lecture2 OVR
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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);
8/23/2019 Java Lecture2 OVR
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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
8/23/2019 Java Lecture2 OVR
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8
. .
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
8/23/2019 Java Lecture2 OVR
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9
. .
final int MAX = 5;
int[] myarray = new int[MAX];
.
. .
(literals)
8/23/2019 Java Lecture2 OVR
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10
. .
(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
8/23/2019 Java Lecture2 OVR
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11
. .
(char)
..
: .. \n, \t, \b, \r, \f (form feed), \\, \, \, \0
(Strings) .. Blah blah \n
. .
:
(..1 ..2)
(.. ..)
(.. ..)
(..1 ..2)
8/23/2019 Java Lecture2 OVR
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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
8/23/2019 Java Lecture2 OVR
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13
. .
..
..
:
.. 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 ()
8/23/2019 Java Lecture2 OVR
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15
. .
: +, -, /, *, %
: =, +=, -=, /=, *=, %=
.. 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)
8/23/2019 Java Lecture2 OVR
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16
. .
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
8/23/2019 Java Lecture2 OVR
18/18
. .
.. 3.14, double. float 3.14F
casting
, java.lang, ..
. .
Math java.lang