Java             3GL - .   4GL -     DB-

JAVA

Java

Java , C++.

 

, Java.

 

if-else

:

if ( ) 1; [ else 2;]

else . , . , boolean.

int bytesAvailable;

// ...

if (bytesAvailable > 0) {

ProcessData();

bytesAvailable -= n;

} else

waitForMoreData();

, , , if-else.

 

class IfElse {

public static void main(String args[]) { int month = 4;

String season;

if (month == 12 || month == 1 || month == 2) {

season = "Winter";

} else if (month ==3 || month == 4 || month == 5) {

season = "Spring";

} else if (month == 6 || month == 7 || month == 8) {

season = "Summer";

} else if (month == 9 || month == 10 || month == 11) {

season = "Autumn";

} else {

season = "Bogus Month";

}

System.out.println( "April is in the " + season  + ".");

} }

 

:

: \> java IfElse

April is in the Spring.

 

break

Java goto. , goto, Java break. , , . Java . break switch . .

 

, , . break, , , b. println.

 

class Break {

public static void main(String args[]) { boolean t = true;

a:      { b:         { c:             {

System.out.println("Before the break"); // break

       if (t)

       break b;

       System.out.println("This won't execute");  // He      }

       System.out.println("This won't execute"); // He      }

       System.out.println("This is after b"); // b      

} } }

 

    :

:\> Java Break

Before the break

This is after b

 

break . break goto , .

 

switch

switch . :

switch ( ) { case 1:

break;

case 2:

break;

case :

break;

default:

}

, , case, switch. . case , .

 

case, , default. , default . , case switch default , switch.

 

switch ( , ) break , switch. break , case . switch case, break.

 

class SwitchSeason { public static void main(String args[]) {

int month = 4;

String season;

switch (month) {

case 12: // FALLSTHROUGH

case 1: // FALLSTHROUGH

case 2:

season = "Winter";

break;

case 3: // FALLSTHROUGH

case 4: // FALLSTHROUGH

case 5:

season = "Spring";

break;

case 6: // FALLSTHROUGH

case 7: // FALLSTHROUGH

case 8:

season = "Summer";

break;

case 9: // FALLSTHROUGH

case 10: // FALLSTHROUGH

case 11:

season = "Autumn";

break;

default:

season = "Bogus Month";

}

System.out.println("April is in the " +    season +     ".");

} }

 

, switch . , .

 

class WordCount {

static String text = "Now is the tifne\n" +

                     "for all good men\n" +

                     "to come to the aid\n" +

                     "of their country\n"+

                     "and pay their due taxes\n";

static int len = text.length();

public static void main(String args[]) {

boolean inWord = false;

int numChars = 0;

int numWords = 0;

int numLines = 0;

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

     char = text.charAt(i);

     numChars++;

     switch () {

             case '\n': numLines++; // FALLSTHROUGH

             case '\t': // FALLSTHROUGH

             case ' ' : if (inWord) {

                            numWords++;

                            inWord = false;

                        }

                        break;

            default: inWord = true;

                }

     }

System.out.println("\t" + numLines +"\t" + numWords + "\t" + numChars);

} }

 

, . 9.

 

return

, Java , . main, -. return, , . , return , Java.

 

class ReturnDemo {

public static void main(String args[]) {

boolean t = true;

System.out.println("Before the return"); // return

if (t) return;

System.out.println("This won't execute"); //

} }

 

if (t)? ,   , Java , println . Java , if .                                       

 

4 , , . Java : while ( -), do-while ( -) for ( ).

 

while

, true. while:

[ ; ]

while ( )     {

;

[;] }

. while tick.

 

class WhileDemo {

public static void main(String args[]) {

int n = 10;

while (n > 0) {

       System.out.println("tick " + n);

       n--;

       }

} }

 

do-while

, false. Java do-while. :

[ ; ] do { ; [;] } while ( );

. :

 

class DoWhile {

public static void main(String args[]) {

int n = 10;

do {

    System.out.println("tick " + n);

   } while (--n > 0);

} }

 

for

. for.

for ( ; ; ) ;

, for, while, . , , . for .

 

class ForDemo {

public static void main(String args[]) {

for (int i = 1; i <= 10; i++)

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

} }

 

      

, .

 

class ForTick {

public static void main(String args[]) {

for (int n = 10; n > 0; n--)

System.out.println("tick " + n);

} }

for. , for, .

 

, for.

 

class Months {

static String months[] = {

"January", "February", March", "April", "May", "June", "July", "August", "September", "October", "November", "December" };

static int monthdays[]   = { 31, 28,  31, 30, 31,  30, 31, 31, 30, 31, 30, 31 };

static String spring = "spring";

static String summer = "summer";

static String autumn = "autumn";

static String winter = "winter";

static String seasons[]  = { winter, winter, spring, spring, spring, summer, summer, summer, autumn, autumn, autumn, winter };

public static void main(String args[]) {

for (int month = 0; month < 12; month++) {

System.out.println(months[month] + " is a "      +

seasons[month] + " month with " + monthdays[month] + " days.");

} } }

 

:

:\> Java Months

January is a winter month with 31 days.

February is a winter month with 28 days.

March is a spring month with 31 days.

April is a spring month with 30 days.

May is a spring month with 31 days.

June is a summer month with 30 days.

July is a summer month with 31 days.

August is a summer month with 31 days.

September is a autumn month with 30 days.

October is a autumn month with 31 days.

November is a autumn month with 30 days.

December a winter month with 31 days.

 

 

, for . for , Java . (,) for. for, .

 

class Comma {

public static void main(String args[]) {

int a, b;

for (a = 1, b = 4; a < b; a++, b--) {

     System.out.println("a = " + a);

     System.out.println("b = " + b);

     }

} }

 

, .

: \> java Comma

= 1

b = 4

= 2

b = 3

 

continue

, , . Java continue. , continue , .

 

class ContinueDemo {

public static void main(String args[]) {

for (int i=0; i < 10; i++) {

     System.out.print(i + " ");

     if (i % 2 == 0) continue;

     System.out.println("");

     }

}}

 

, . :

: \> java ContinueDemo

0 1

2 3

4 5

5 7

8 9

 

break, continue , , . , continue 0 9:

 

class ContinueLabel {

public static void main(String args[]) {

outer:   for (int i=0; i < 10; i++) {

              for (int j = 0; j < 10; j++) {

                   if (j > i) {

                       System.out.println("");

                       continue outer;

                   }

              System.out.print(" " + (i * j));

              }

         }

}}

 

continue j i. :

:\> Java ContinueLabel

0

0 1

0 2 4

0 3 6 9

0 4 8 12 16

0 5 10 15 20 25

0 6 12 18 24 30 36

0 7 14 21 28 35 42 49

0 8 16 24 32 40 48 56 64

0 9 18 27 36 45 54 63 72 81

 

Java . try, catch, throw finally. 10 .

Java . , . Java . , , - .

 

 

Java             3GL - .   4GL -     DB-


, , - . , , . , .




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