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FAQ

Java.lang.String Java SE 6

⇐ 12345678910 ⇒



Java.lang.Integer 71

Optional: ob1 Integer ob2 String . generic- Object, , ob3. , .

generic- <T>, , . Object. , .

, :

public class OptionalExt <T extends T> {

Private T value;

}

, , () T, (bound) .

, . ?. extends .

/* # 11: : Mark.java, Runner.java */

package chapt03;

 

public class Mark<T extends Number> {

public T mark;

 

public Mark(T value) {

mark = value;

}

public T getMark() {

return mark;

}

public int roundMark() {

return Math. round (mark.floatValue());

}

/* */ // public boolean sameAny(Mark<T> ob) {

public boolean sameAny(Mark<?> ob) {

return roundMark() == ob.roundMark();

}

public boolean same(Mark<T> ob) {

return getMark() == ob.getMark();

}

}

package chapt03;

 

public class Runner {

public static void main(String[] args) {

// Mark<String> ms = new Mark<String>(7); //

Mark<Double> md = new Mark<Double>(71.4D); //71.5d

System. out. println(md.sameAny(md));

Mark<Integer> mi = new Mark<Integer>(71);

System. out. println(md.sameAny(mi));

// md.same(mi); //

System. out. println(md.roundMark());

}

}

:

True

True

sameAny(Mark<?> ob) Mark, , Mark<T> , .

generic- . , generic-:

class Optional <T> {

T value = new T();

}

, .

generic- , generic- generic-, :

/* # 12: : Failed.java */

package chapt03;

class Failed <T1, T2> {

static T1 value;

T2 id;

 

static T1 getValue() {

return value;

}

static void use() {

System. out. print(id);

}

}

(generic) , , , , , :

<T extends > returnType methodName(T arg) {}

<T> returnType methodName(T arg) {}

. , , , extends. .

Generic- , . . generic-.

/* # 13: : GenericMethod.java */

public class GenericMethod {

public static <T extends Number> byte asByte(T num) {

long n = num.longValue();

if (n >= -128 && n <= 127) return (byte)n;

else return 0;

}

public static void main(String [] args) {

System. out. println(asByte (7));

System. out. println(asByte (new Float("7.f")));

// System.out.println(asByte(new Character('7'))); //

}

}

Integer (int ) Float Number, . Character , asByte(T num).

.

/* # 14: : DemoVarargs.java */

package chapt03;

 

public class DemoVarargs {

public static int getArgCount(Integer... args) {

if (args.length == 0)

System. out. print("No arg=");

for (int i: args)

System. out. print("arg:" + i + " ");

return args.length;

}

public static void main(String args[]) {

System. out. println("N=" + getArgCount (7, 71, 555));

Integer[] i = { 1, 2, 3, 4, 5, 6, 7 };

System. out. println("N=" + getArgCount (i));

System. out. println(getArgCount ());

}

}

:

arg:7 arg:71 arg:555 N=3

arg:1 arg:2 arg:3 arg:4 arg:5 arg:6 arg:7 N=7

No arg=0

. getArgCount() . . . .

, :

void methodName([]... args){}

:

void methodName(Integer...args) {}

void methodName(int x1, int x2) {}

void methodName(String...args) {}

. Object... args , :

/* # 15: : DemoOverload.java */

package chapt03;

 

public class DemoOverload {

public static void printArgCount(Object... args) { //1

System. out. println("Object args: " + args.length);

}

public static void printArgCount(Integer[]...args){ //2

System. out. println("Integer[] args: " + args.length);

}

public static void printArgCount(int... args) { //3

System. out. print("int args: " + +args.length);

}

public static void main(String[] args) {

Integer[] i = { 1, 2, 3, 4, 5 };

 

printArgCount (7, "No", true, null);

printArgCount (i, i, i);

printArgCount (i, 4, 71);

printArgCount (i); // 1

printArgCount (5, 7);

// printArgCount();//!

}

}

:

Object args: 4

Integer[] args: 3

Object args: 3

Object args: 5

int args: 2

printArgCount() i Object... args, . Integer[]...args , Object[]...args. Integer[]...args Object...args.

- .

.

,
...args , :

void methodName(1 obj, 2... args) {}

(typesafe enums) Java java.lang.Enum. new. .

:

/* # 16: : SimpleUseEnum.java */

package chapt02;

enum Faculty {

MMF, FPMI, GEO

}

public class SimpleUseEnum {

public static void main(String args[]) {

Faculty current;

current = Faculty. GEO;

switch (current) {

case GEO:

System. out. print(current);

break;

case MMF:

System. out. print(current);

break;

// case LAW: System.out.print(current);// !

default:

System. out. print(" case: " + current);

}

}

}

case , switch.

Enum , , . enum :

static enumType[] values() , ;

static T valueOf(Class<T> enumType, String arg) , ;

static enumType valueOf(String arg) , ;

int ordinal() .

/* # 17: : Shape.java */

package chapt02;

 

enum Shape {

RECTANGLE, TRIANGLE, CIRCLE;

public double square(double x, double y) {

switch (this) {

case RECTANGLE:

return x * y;

case TRIANGLE:

return x * y / 2;

case CIRCLE:

return Math. pow (x, 2) * Math. PI;

}

throw new EnumConstantNotPresentException(

this. getDeclaringClass(), this. name());

}

}

/* # 18: : Runner.java */

package chapt02;

 

public class Runner {

public static void main(String args[]) {

double x = 2, y = 3;

Shape[] arr = Shape. values ();

for (Shape sh: arr)

System. out. printf("%10s = %5.2f%n",

sh, sh.square(x, y));

}

}

:

RECTANGLE = 6,00

TRIANGLE = 3,00

CIRCLE = 12,57

, square(). throw , . . case.

/* # 19: : DeanDemo.java */

package chapt02;

enum Dean {

MMF (""), FPMI (""), GEO ("");

String name;

 

Dean(String arg) {

name = arg;

}

String getName() {

return name;

}

}

package chapt02;

public class DeanDemo {

public static void main(String[] args) {

Dean dn = Dean. valueOf ("FPMI");

System. out. print(dn.ordinal());

System. out. println(": " + dn + ": " + dn.getName());

}

}

:

1: FPMI:

.

:

Ÿ ;

Ÿ ;

Ÿ ;

Ÿ , new.

-, , , , , , . , , . , .

.

/* # 20: : RequestForCustomer.java */

package chapt03;

 

public @interface RequestForCustomer {

int level();

String description();

String date();

}

interface @. . -: int level(), String description(), String date().

, , . , , throws . : , String, Enum, Class .

java.lang.annotation.Annotation. : hashCode(), equals() toString(), Object. annotationType(), lass, .

. , . , , , , enum. . .

, -. , RequestForCustomer :

@RequestForCustomer (

level = 2,

description = "Enable time",

date = "10/10/2007"

)

public void customerThroughTime() {

//...

}

customerThroughTime(). , @, -. -, . , "Enable time" description(), RequestForCustomer. description . - , . , - .

/* # 21: : Request.java */

package chapt03;

import java.lang.reflect.Method;

 

public class Request {

@RequestForCustomer(level = 2,

description = "Enable time",

date = "10/10/2007")

public void customerThroughTime() {

try {

Class c = this. getClass();

Method m = c.getMethod("customerThroughTime");

RequestForCustomer ann =

m.getAnnotation(RequestForCustomer. class);

//

System. out. println(ann.level() + " "

+ ann.description() + " "

+ ann.date());

} catch (NoSuchMethodException e) {

System. out. println(" ");

}

}

public static void main(String[] args) {

Request ob = new Request();

ob.customerThroughTime();

}

}

:

2 Enable time 10/10/2007

, RUNTIME

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy. RUNTIME) //

, .

SOURCE .

CLASS .class, JVM .

, RUNTIME, .class JVM . , RUNTIME .

: -, .

- -. . . - -, .

public @interface TigerAnnotation {}

- isAnnotationPresent().

-. -. -, . - . , - value().

-. (_ = ) .

Java , @Retention, @Documented, @Target @Inherited java. lang. annotation. @Override, @Deprecated @Suppresswarnings java. lang.

.

3

A

1. n. , , , , , . m . , . .

2. n. . , , , , . . , , .

3. R3. , , . m . , .

4. (n x n). . , , . . , . , .

5. (m x n). . . , k- . , i- .

6. , , , . n, x, a[n].

7. (m,n). . , , . k , / . , .

8. . . , , , , . n . , .

9. . . , , /. .

10. (BoolMatrix) (n x m). . (), . .

11. (BoolVector) n. . , , .

12. n. . ; , , . , , (), , . , , , .

13. n. . m , . . : /.

14. . . . .

15. . . , , , , ( ).

16. . . : ( ); -, ( ), : ( ), ( ), , ( ).

17. . . , , , , . .

B

, . set (), get (), toString(). , . .

1. Student: id, , , , , , , , , .

. :

a) ;

b) ;

c) , ;

d) .

2. Customer: id, , , , , , .

. :

a) ;

b) , .

3. Patient: id, , , , , , , .

. :

a) , ;

b) , .

4. Abiturient: id, , , , , , .

. :

a) , ;

b) , ;

c) n , ( , ).

5. Book: id, , (), , , , , .

. :

a) ;

b) , ;

c) , .

6. House: id, , , , , , , .

. :

a) , ;

b) , , ;

c) , , .

7. Phone: id, , , , , , , , .

. :

a) , ;

b) , ;

c) .

8. Car: id, , , , , , .

. :

a) ;

b) , n ;

c) , .

9. Product: id, , UPC, , , , .

. :

a) ;

b) , ;

c) , .

10. Train: , , , (, , , ).

. :

a) , ;

b) , ;

c) , .

11. Bus: , , , , , .

. :

a) ;

b) , 10 ;

c) , 100000 .

12. Airlines: , , , , .

. :

a) ;

b) ;

c) , .

3

3.1.

?

1) private;

2) final;

3) native;

4) abstract;

5) protected.

3.2.

Quest3, "".

public class Quest3 {

Quest3 (int i){ System.out.print(""); }

public static void main(String[] args){

Quest3 s= new Quest3();

//1

}

public Quest3() {

//2

}

{

//3

} }

1) //1 Quest3(1);

2) //2 Quest3(1);

3) //3 new Quest3(1);

4) //3 Quest3(1).

3.3.

?

1) nonstatic- ;

2) static- ;

3) private- ;

4) final- .

3.4.

:

public class Quest5 {

{System.out.print("1");}

static {System.out.print("2");}

Quest5(){System.out.print("3");}

public static void main(String[] args) {

System.out.print("4");

} }

:

1) 1234;

2) 4;

3) 34;

4) 24;

5) 14.

 

 
4

, () () , .

, extends. , implements. , . ,
private ( ) .
( extends ) Object.

, , , , . ,
, .

, . , , .

() , , .

.

.

typeEmployee() Employee Manager. , .

/* # 1: :

Employee.java: Manager.java: Runner.java */

package chapt04;

 

public class Employee { //

private int id;

public Employee(int idc) {

super (); /* ,

*/

id = idc;

}

public int getId() {

return id;

}

public void typeEmployee() {

//...

System. out. println("");

}

}

 

package chapt04;

// ,

 

public class Manager extends Employee {

private int idProject;

 

public Manager(int idc, int idp) {

super (idc); /*

*/

idProject = idp;

}

public int getIdProject() {

return idProject;

}

public void typeEmployee() {

//...

System. out. println("");

}

}

package chapt04;

 

public class Runner {

public static void main(String[] args) {

Employee b1 = new Employee(7110);

Employee b2 = new Manager(9251, 31);

b1.typeEmployee(); // Employee

b2.typeEmployee(); // Manager

// b2.getIdProject();// !!!

((Manager) b2).getIdProject();

Manager b3 = new Manager(9711, 35);

System. out. println(b3.getIdProject()); // 35

System. out. println(b3.getId()); // 9711

}

}

b1 Employee, , , typeEmployee() Employee. b2 Employee Manager. , .

(, , ) , .
, , .
this,
super. :

/* # 2: : Course.java: BaseCourse.java: Logic.java */

package chapt04;

 

public class Course {

public int id = 71;

 

public Course() {

System. out. println(" Course");

id = getId(); //!!!

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

}

public int getId() {

System. out. println("getId() Course");

return id;

}

}

package chapt04;

 

public class BaseCourse extends Course {

public int id = 90; // !

 

public BaseCourse() {

System. out. println(" BaseCourse");

System. out. println(" id=" + getId());

}

public int getId() {

System. out. println("getId() BaseCourse");

return id;

}

}

package chapt04;

 

public class Logic {

public static void main(String[] args) {

Course objA = new BaseCourse();

BaseCourse objB = new BaseCourse();

System. out. println("objA: id=" + objA.id);

System. out. println("objB: id=" + objB.id);

Course objC = new Course();

}

}

:

Course

GetId() BaseCourse

id=0

⇐ 12345678910 ⇒


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