Java             3GL - .   4GL -     DB-

JAVA

Java

Java . Java , , - . , Exception. , . , .

Java 5 : try, catch, throw, throws finally. . (try) , , (throw) , (catch) (finally) .

.

try {

// }

catch (1 ) {

// 1 }

catch (2 ) {

// 2

 throw(e)   // }

finally {

}

Delphi catch except.

 

Throwable. Throwable. Throwable . ception , . Throwable Error, , .

 

- Java . , , .

 

class Exc0 {

public static void main(string args[]) {

int d = 0;

int a = 42 / d;

} }

 

, .

:\> java Exc0

java.lang.ArithmeticException: / by zero

at Exc0.main(Exc0.java:4)

 

Exception Throwable. Exception, : ArithmeticException, , . , , main.

 

class Exc1 {

static void subroutine() {

int d = 0;

int a = 10 / d;

}

public static void main(String args[]) {

Exc1.subroutine();

} }

 

, Java .

:\> java Exc1

java.lang.ArithmeticException: / by zero

at Exc1.subroutine(Exc1.java:4)

at Exc1.main(Exc1.java:7)

 

try catch

, , try. try- catch, .

 

class Exc2 {

public static void main(String args[]) {

try {

    int d = 0;

     int a = 42 / d;

    }

catch (ArithmeticException e) {

System.out.println("division by zero");

}

} }

 

catch- , , ( division by zero).

 

catch

. , , Java catch- try-. , , . , catch , Throwable.

 

class MultiCatch {

public static void main(String args[]) {

try {

     int a = args.length;

     System.out.println("a = " + a);

     int b = 42 / a;

     int c[] = { 1 };

     c[42] = 99;

    }

catch (ArithmeticException e) {

System.out.println("div by 0: " + e);

}

catch(ArrayIndexOutOfBoundsException e) {

System.out.println("array index oob: " + e);

}

} }

 

, , . , , , ArrayIndexOutOf Bounds. , .

:\> java MultiCatch

= 0

div by 0: java.lang.ArithmeticException: / by zero

C:\> java MultiCatch 1

a = 1

array index oob: java.lang.ArrayIndexOutOfBoundsException: 42

 

try

try , . try catch, , , catch try. , try .

 

class MultiNest {

static void procedure() {

try {

     int c[] = { 1 };

     c[42] = 99;

}

catch(ArrayIndexOutOfBoundsException e) {

System.out.println("array index oob: " + e);

} }

public static void main(String args[]) {

try {

     int a = args.length();

     System.out.println("a = " + a);

     int b = 42 / a;

     procedure();

}

catch (ArithmeticException e) {

System.out.println("div by 0: " + e);

}

} }

 

throw

throw . , , Throwable, catch, new. throw.

throw Throwable;

 

, . try catch. , . , try, catch, Java , . , -, throw , catch.

 

class ThrowDemo {

static void demoproc() {

try {

throw new NullPointerException("demo");

}

catch (NullPointerException e) {

System.out.println("caught inside demoproc");

throw e;

} }

public static void main(String args[]) {

try {

demoproc();

}

catch(NulPointerException e) {

System.out.println("recaught: " + e);

}

} }

 

. main demoproc. demoproc , NullPointerException throw . demoproc, - e. , , throw, main. , .

 

:\> java ThrowDemo

caught inside demoproc

recaught: java.lang.NullPointerException: demo

 

throws

, , , . , , throws. (.. throw) , throws . :

 

_( ) throws _ {}

 

, procedure , , . .

 

class ThrowsDemo1 {

static void procedure() {

System.out.println("inside procedure");

throw new IllegalAccessException("demo");

}

public static void main(String args[]) {

procedure();

} }

 

, , , procedure IllegalAccessException main :

 

class ThrowsDemo {

static void procedure() throws IllegalAccessException {

System.out.println(" inside procedure");

throw new IllegalAccessException("demo");

}

public static void main(String args[]) {

try {

procedure();

}

catch (IllegalAccessException e) {

System.out.println("caught " + e);

}

} }

 

.

:\> java ThrowsDemo

inside procedure

caught java.lang.IllegalAccessException: demo

 

finally

, , . finally. , catch, finally , , try. try catch finally. finally , .      , , finally.

 

class FinallyDemo {

static void procA() {

try {

System.out.println("inside procA");

throw new RuntimeException("demo");

}

finally {

System.out.println("procA's finally");

} }

static void procB() {

try {

System.out.println("inside procB");

return;

}

finally {

System.out.println("procB's finally");

} }

public static void main(String args[]) {

try {

procA();

}

catch (Exception e) {}

procB();

} }

 

procA - try, finally. procB try- return, finally. , .

 

:\> java FinallyDemo

inside procA

procA's finally

inside procB

procB's finally

 

Exception

Throwable . int, char .., , Throwable, , String Object, . Exception. , Exception.

 

class MyException extends Exception {

private int detail;

MyException(int a) {

detail = a:

}

public String toString() {

return "MyException[" + detail + "]";

}

}

class ExceptionDemo {

static void compute(int a) throws MyException {

System.out.println("called computer + a + ").");

if (a > 10)

throw new MyException(a);

System.out.println("normal exit.");

}

public static void main(String args[]) {

try {

compute(1);

compute(20);

}

catch (MyException e) {

System.out.println("caught" + e);

}

} }

 

. MyException Exception. , , toString, , -. ExceptionDemo compute, MyExcepton. compute , - 10. main compute , ( 10), . .

 

:\> java ExceptionDemo

called compute(1).

normal exit.

called compute(20).

caught MyException[20]

 

. Try, throw, catch . , , , , .

 

Java             3GL - .   4GL -     DB-


, Instance, - - . .




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