.


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( , )

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FAQ

⇐ 12345678910 ⇒



| >>
|= ( ) >>= ( )
& >>>
&= (c ) >>>=
^ <<
^= (c ) <<=
~    

< >
<= >=
== !=

, , .

|| &&
!    

instanceof ?: (if-then-else).

boolean Boolean (true false).

// # 2: %: DemoOperators.java

package chapt02;

public class DemoOperators {

public static void main(String[] args) {

System. out. println("5%1=" + 5%1 + " 5%2=" + 5%2);

int b1 = 0xe;//14 1110

int b2 = 0x9;//9 1001

int i = 0;

System. out. println(b1 + "|" + b2 + " = " + (b1|b2));

System. out. println(b1 + "&" + b2 + " = " + (b1&b2));

System. out. println(b1 + "^" + b2 + " = " + (b1^b2));

System. out. println("~" + b2 + " = " + ~b2);

System. out. println(b1 + ">>" + ++i + " = " + (b1>>i));

System. out. println(b1 + "<<" + i + " = " + (b1<<i++));

System. out. println(b1 + ">>>" + i +" = " + (b1>>>i));

}

}

:

5%1=0 5%2=1

14|9 = 15

14&9 = 8

14^9 = 7

~9 = -10

14>>1 = 7

14<<1 = 28

14>>>2 = 3

"? " :

boolean? :

boolean true, , .

instanceof true, . , :

class Course extends Object {}

class BaseCourse extends Course {}

class FreeCourse extends BaseCourse {}

BaseCourse
Course
FreeCourse
OptionalCourse

class OptionalCourse extends Course {}

. 2.2.

instanceof doLogic(Course c):

void doLogic(Course c) {

if (c instanceof BaseCourse) { /* BaseCourse

FreeCourse*/

} else if (c instanceof OptionalCourse) { /*

OptionalCourse*/

} else { /* Course*/ }

}

instanceof , , . Object , Object. null , null - . null . null , instanceof.

-

, Java - (wrapper-) java.lang: Boolean, Character, Integer, Byte, Short, Long, Float, Double. , .

Float
Number
+
byteValue(): byte
+
doubleValue(): double
+
floatValue(): float
 
+
intValue(): int
+
longValue(): long
+
shortValue(): short
interface
Comparable
Integer
Byte
Double
Long
Short
Character
Void
Boolean
+
booleanValue(): boolean
+
equals(Object): boolean
+
getBoolean(String): boolean
+
compareTo(Boolean): int
+
parseBoolean(String): boolean
+
valueOf(): Boolean

. 2.3. -

, , - . , , java.lang, Number Comparable, . - null.

, . Value() .

Character Number, , . Character . Character, , String.

/* # 3: : CastTypes.java */

package chapt02;

public class CastTypes {

public static void main(String[] args) {

Float f1 = new Float(10.71); // double Float

String s1 = Float. toString (0f); // float String

String s2 = String. valueOf (f1); // Float String

Byte b = Byte. valueOf ("120"); // String Byte

double d = b.doubleValue(); // Byte double

byte b0=(byte)(float)f1; // Float byte

//b2 = (byte)f1; // !!!

/*f1 , */

short s = (short) d; // double short

/* Character int */

Character ch = new Character('3');

int i = Character. digit (ch.charValue(), 10);

System. out. printf("f1=%1.2e s1=%s s2=%s%n", f1, s1, s2);

System. out. printf("b=%o d=%.1f b0=%d s=%d i=%d",

b, d, b0, s, i);

}

}

:

f1=1.07e+01 s1=0.0 s2=10.71

b=170 d=120,0 b0=10 s=120 i=3

valueOf(String str) -, , , , .

Java
java.math.BigInteger java.math.BigDecimal, .

Java String. String " + " . '\0', ASCII-, .

5.0 (). new. :

Integer iob = 71;

- . , intValue(), doubleValue() .

, , / :

// # 4: autoboxing & unboxing: NewProperties.java

package chapt02;

public class NewProperties {

public static void main(String[] args) {

Integer j = 71; // +

Integer k = ++j; //++

int i = 2;

k = i + j + k;

}

}


NullPointerException null Integer:

Integer j = null; // !

int i = j; //

, -, .

int i = 128; // 127!!!

Integer oa = i; // +

Integer ob = i;

System. out. println("oa==i " + (oa == i)); // true

System. out. println("ob==i " + (ob == i)); // true

System. out. println("oa==ob " + (oa == ob)); // false( )

System. out. println("equals ->" + oa.equals(i)

+ ob.equals(i)

+ oa.equals(ob)); // true

equals() , , . oa.equals(ob) true.

equals(). :

boolean b = i.equals(oa); //

- ,

Float f = 7; // (float)7 7F 7

.

, , , Number, :

Number n1 = 1;

Number n2 = 7.1;

Number array[] = {71, 7.1, 7L};

.

, - .

if :

if (boolexp) { /**/ } //1

else { /**/ } //2

boolexp true, 1, 2. else , if ( 2), if. - if {} else if {}.

C++ switch:

switch (exp) {

case exp1:{ /**/ }

Break;

case expN:{ /**/ }

Break;

default: { /**/ }

}

exp==exp1 , break, exp1,, expN int, byte, short, char enum.

, . if , , else . switch case ( ), default.

Java , ++:

while (boolexp) { /**/ } //

do { /**/ } while (boolexp); //

 

for (exp1; boolexp; exp3){ /**/ } //

exp1 , boolexp , exp3 , ( , ). , boolexp true.

:

- , for while , do/while .

- for . while , , , . while(true).

- for .

- , .

- .

- . .

- .

5.0 , :

for ( : ){ /**/ }

.

int [] array = {1, 3, 5};

for (int i: array) //

System. out. printf("%d ", i); //

. , Iterable Iterator.

Java break continue, , :

int j = -3;

OUT: while (true) {

for (;;)

while (j < 10) {

if (j == 0)

break OUT;

else {

j++;

System. out. printf("%d ", j);

}

}

}

System. out. print("end");

break , OUT. goto .

, . . . Java , new . , , null . , : int a[]. int[] a.

/* # 5: : ArrRef.java */

package chapt02;

public class ArrRef {

public static void main(String[] args) {

int myRef[], my; //

float [] myRefFloat, myFloat; // !

//

int myDyn[] = new int [10];

/* */

int myInt[] = {5, 7, 9, -5, 6, -2}; //6

byte myByte[] = {1, 3, 5}; //3

/* Object */

Object myObj = new float [5];

//

myRef = myDyn;

myDyn = myInt;

myRefFloat = (float [])myObj;

myObj = myByte; //

myRefFloat = (float [])myObj; //

// ()

// myInt = myByte;

//myInt = (int [])myByte;

}

}

Object . , . , . .

myDyn=myInt , myDyn myInt, .

, . length.

Java , . , :

int arr[][] = { { 1 },

{ 2, 3 },

{ 4, 5, 6 },

{ 7, 8, 9, 0 }

};

, arr[2][0] , 4.

Matrix
-
a: int[][]
+
Matrix(int, int)
+
getHorizontalSize(): int
+
getVerticalSize(): int
+
getElement(int, int): int  
+
setElement(int, int, int): void
+
toString(): String
MatrixFactory
+
createRandomized(int, int): Matrix
Multiplicator
+
multiply(Matrix, Matrix): void

() .

. 2.4.

/* # 6: : Matrix.java */

package chapt02;

 

public class Matrix {

private int [][] a;

 

public Matrix(int n, int m) {

//

a = new int [n][m];

}

public int getVerticalSize() {

return a.length;

}

public int getHorizontalSize() {

return a[0].length;

}

public int getElement(int i, int j) {

return a[i][j];

}

public void setElement(int i, int j, int value) {

a[i][j] = value;

}

public String toString() {

String s = "\nMatrix: " + a.length +

"x" + a[0].length + "\n";

for (int [] vector: a) {

for (int value: vector)

s+= value+" ";

s += "\n";

}

return s;

}

}

/* # 7: - : MatrixFactory.java */

package chapt02;

 

public class MatrixFactory {

 

public static Matrix createRandomized(int n, int m) {

Matrix matrix = new Matrix(n, m);

for (int i = 0; i < n; i++) {

for (int j = 0; j < m; j++) {

matrix.setElement(i, j, (int)(Math. random ()*m*m));

}

}

return matrix;

}

}

/* # 8: : Multiplicator.java */

package chapt02;

 

public class Multiplicator {

 

public static Matrix multiply(Matrix p, Matrix q)

throws MultipleException {

int v = p.getVerticalSize();

int h = q.getHorizontalSize();

int temp = p.getHorizontalSize();

//

if (temp!= q.getVerticalSize())

throw new MultipleException();

//

Matrix result = new Matrix(v, h);

//

for (int i = 0; i < v; i++)

for (int j = 0; j < h; j++) {

int value = 0;

for (int k = 0; k < temp; k++) {

value += p.getElement(i, k) * q.getElement(k, j);

}

result.setElement(i, j, value);

}

return result;

}

}

/* # 9: : MultipleException.java */

package chapt02;

public class MultipleException extends Exception {}

/* # 10: , : Runner.java */

package chapt02;

public class Runner {

public static void main(String[] args) {

int n = 2, m = 3, l = 4;

Matrix p = MatrixFactory. createRandomized (n, m);

Matrix q = MatrixFactory. createRandomized (m, l);

System. out. println("Matrix first is: " + p);

System. out. println("Matrix second is: " + q);

 

try {

Matrix result = Multiplicator. multiply (p, q);

System. out. println("Matrix product is: "

+ result);

} catch (MultipleException e){

System. err. println("Matrices could"

+ " not be multiplied: ");

}

}

}

random(), :

Matrix first is:

Matrix: 2x3

6 4 2

0 8 4

Matrix second is:

Matrix: 3x4

8 0 2 7

6 1 0 0

1 2 4 5

Matrix product is:

Matrix: 2x4

74 8 20 52

52 16 16 20

. , null. .

th

java.lang.Math , E PI.

( Math ). , , floor(), ceil(), rint(), round(), max(), min(), , , .. , random() Math.

/* # 11: Math: MathMethods.java */

package chapt02;

public class MathMethods {

public static void main(String[] args) {

final int MAX_VALUE = 10;

double d;

d = Math. random () * MAX_VALUE;

System. out. println("d = " + d);

System. out. println(" ="

+ Math. round (d));

System. out. println(" , "

+ " <= ="

+ Math. floor (d));

System. out. println(" , "

+ " >= ="

+ Math. ceil (d));

System. out. println(" "

+ " =" + Math. rint (d));

}

}

:

d = 0.08439575016076173

=0

, <= =0.0

, >= =1.0

=0.0

java.lang. java.lang.System, . .

, System.in, System.out System.err, / , :

void gc() ;

void exit(int status) java- (JVM);

void setIn(InputStream in), void setOut(PrintStream out),
void setErr(PrintStream err) /;

Properties getProperties() ;

String getProperty(String key) ;

void setSecurityManager(SecurityManager s), SecurityManager getSecurityManager() ;

void load(String filename) ;

void loadLibrary(String libname) ;

void arrayCopy( ) .


java.lang.Runtime. Runtime getRuntime(), Runtime, . exit(int status) halt(int status). : gc(),
runFinalization() . totalMemory() freeMemory().

/* # 12: : RuntimeDemo.java*/

package chapt02;

public class RuntimeDemo {

public static void main(String[] args) {

Runtime rt = Runtime. getRuntime ();

System. out. println(" : "

+ rt.totalMemory());

System. out. println(" : "

+ rt.freeMemory());

double d[] = new double [10000];

System. out. println(" " +

" : " + rt.freeMemory());

//

ProcessBuilder pb =

new ProcessBuilder("mspaint","c:\\temp\\cow.gif");

 

try {

pb.start(); // mspaint.exe

} catch (java.io.IOException e) {

System. err. println(e.getMessage());

}

System. out. println(" "

+ " mspaint.exe: " + rt.freeMemory());

System. out. println(" : "

+ pb.command());

}

}

, , :

: 2031616

: 1903632

: 1823336

mspaint.exe: 1819680

: [mspaint, c:\temp\cow.gif]


java.lang.ProcessBuilder, start(), . .

arraycopy() System, , .

/* # 13: : ArrayCopyDemo.java */

package chapt02;

public class ArrayCopyDemo {

public static void main(String[] args) {

int mas1[] = { 1, 2, 3 },

mas2[] = { 4, 5, 6, 7, 8, 9 };

show ("mas1[]: ", mas1);

show ("mas2[]: ", mas2);

// mas1[] mas2[]

System. arraycopy (mas1, 0, mas2, 2, 3);

/*

0 mas1[] ,

2 , ,

3

*/

System. out. printf("%n arraycopy(): ");

show ("mas1[]: ", mas1);

show ("mas2[]: ", mas2);

}

private static void show(String s, int [] mas) {

System. out. printf("%n%s", s);

for (int i: mas) System. out. printf("%d ", i);

}

}

:

mas1[]: 1 2 3

mas2[]: 4 5 6 7 8 9

arraycopy():

mas1[]: 1 2 3

mas2[]: 4 5 1 2 3 9

2

A

, , . Date. /** */, HTML- Web-.

1. n , . .

2. n . () .

3. n . , () , .

4. n . , . , .

5. n . , , .

6. n . , . , .

7. n . , . , .

8. n . , , -. , .

9. 18, .

10. switch, , k (-10k, 0], (0, 5], (5, 10], (10, 10k].

11. switch, , k (-10k, 5], [0, 10], [5, 15], [10, 10k].

12. , 1 25 5x5 .

13. , . .

14. 1 12. , . ( ).

n a [ n ][ n ]. - n n .

1. () k - ().

2. k (, , ).

3. () , .

4. , .

5. .

6. .

7. 90 (180, 270) .

8. .

9. , .

10. () , .

11. , , .

12. .

13. , , , .

14. .

15. . ( i,j, i,j i - j - ).

16. , , .

17. . ( , . , .)

18. . ( , .)

19. , , . ( ).

20. , , (2,2), (3,3) . ., .

2

2.1.

?

1) float f = 7.0;

2) char c = "z";

3) byte b = 255;

4) boolean n = null;

5) int i = 32565;

6) int j = .

2.2.

?

1) if (i<j) { System.out.print("-1-"); }

2) if (i<j) then System.out.print("-2-");

3) if i<j { System.out.print("-3-"); }

4) if [i<j] System.out.print("-4-");

5) if (i<j) System.out.print("-5-");

6) if {i<j} then System.out.print("-6-");.

2.3.

?

1) 2int;

2) int_#;

3) _int;

4) _2_;

5) $int;

6) #int.

2.4.

?

int a1[] = {};

int a2[] = new int []{1,2,3};

int a3[] = new int [](1,2,3);

int a4[] = new int [3];

int a5[] = new int [3]{1,2,3};

1) a1;

2) a2;

3) a3;

4) a4;

5) a5.

 
3

, , .

Java, , , . . , , , .

. , , .

. / , .

:

class {

{} //

//

private //

protected //

public //

}

. :

c ;

Java , static () , , . public, private, protected . , . , , .

final . final , , .

, :

/* # 1: : Second.java */

package chapt03;

import java.util.*;

 

class Second {

private int x; //

private int y = 71; //

public final int CURRENT_YEAR = 2007; //

protected static int bonus; //

static String version = "Java SE 6"; //

protected Calendar now;

public int method(int z) { //

z++;

int a; //

//a++; // ,

a = 4; //

a++;

now = Calendar. getInstance (); //

return a + x + y + z;

}

}

, , ( String). , new.

Java , . - Java :

, ;

private ;

protected , , ;

public .

( ), public, . , private, . , . . , , , , protected. , .

public (enclosing) . , .

- , . , ; , new . , .

Java , ( ). finalize(). Java , , .

/* # 2: : Quest.java */

package chapt03;

 

public class Quest {

private int id;

private String text;

// ( )

public Quest() {

super (); /* ,

*/

}

//

public Quest(int idc, String txt) {

super (); /*

, */

id = idc;

text = txt;

}

}

Quest , :

Quest a = new Quest(); //

Quest b = new Quest(71, " boolean?");

new , , .

, Java , , : 0, false, null. , . . . , :

super( );

Point c (), .

/* # 3: : Point.java: LocateLogic.java: Runner.java */

package chapt03;

 

public class Point {

/* */

private final double x;

private final double y;

 

public Point(final double xx, final double yy) {

super ();

x = xx;

y = yy;

}

public double getX() {

return x;

}

public double getY() {

return y;

}

}

package chapt03;

 

public class LocateLogic {

public double calculateDistance(

Point t1, Point t2) {

/* */

double dx = t1.getX() - t2.getX();

double dy = t1.getY() - t2.getY();

return Math. hypot (dx, dy);

}

}

package chapt03;

public class Runner {

public static void main(String[] args) {

//

Point t1 = new Point(5, 10);

Point t2 = new Point(2, 6);

System. out. print(" : "

+ new LocateLogic().calculateDistance(t1, t2));

}

}

:

: 5.0

public, . private , . protected .

. .

Java . :

returnType methodName(_) {

//

return value; // (returnType void)

}

, return , void. void , . ( ):

ObjectName.methodName();

- new.

, . ( void) . , , .

[] [static] [abstract] [final] [native]

[synchronized] returnType methodName(_)

[throws _]

, public, private, protected . .

, , .

, static, . , . , static. , this , . , . this , , .

// # 4: : Mark.java

package chapt03;

 

public class Mark {

private int mark = 3;

public static int coeff = 5;

 

public double getResult() {

return (double) coeff *mark/100;

}

public static void setCoeffFloat(float c) {

coeff = (int) coeff*c;;

}

public void setMark(int mark) {

this. mark = mark;

}

//

/*public static int getResult() {

setMark(5);//

return coeff*mark/100;//

}*/

}

Mark ob1 = new Mark();

Mark ob2 = new Mark();

ob1.coeff ob2.coeff 5, . :

Mark.coeff = 7;

:
ClassName. methodName (), :

Mark. setCoeffFloat ();

float z = Math. max (x, y); //

System. exit (1); //

, , .

, , .

final

final , . , final, , . :

/* # 5: final- : Rector.java: ProRector.java */

package chapt03;

 

public class Rector {

 

//

final int ID = (int)(Math. random ()*10);

//

final String NAME_RECTOR;

 

public Rector() {

//

NAME_RECTOR = ""; // !!!

}

// {NAME_RECTOR = "";} // !!!

 

public final void jobRector() {

//

// ID = 100; //!

}

⇐ 12345678910 ⇒


:

: 2016-04-03; !; : 883 |

:

:

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==> ...

1878 - | 1666 -


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