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// Declare some variables

byte centuries = 20;

short years = 2000;

int days = 730480;

long hours = 17531520;

// Print the result on the console

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double doublePI = 3.14;

float double. , , ( , ). 6 9 , 15 17 .

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double doublePI = 3.141592653589793238;


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System.out.println("Double PI is: " + doublePI);

, :

Float PI is: 3.1415927

Double PI is: 3.141592653589793

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float sum = 0.1f + 0.1f + 0.1f + 0.1f + 0.1f +

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float num = 1.0f;

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int a = 1;

int b = 2;

// Which one is greater?

boolean greaterAB = (a > b);

// Is it equal to 1?

boolean equalA1 = (a == 1);


if (greaterAB) {

System.out.println("A > B");

} else {

System.out.println("A >>

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int z = 4 + 8;

System.out.println(z); // 12

String firstName = "Lachezar";

String lastName = "Bozhkov";

// Do not forget the interval between them

String fullName = firstName + " " + lastName;

System.out.println(fullName); // Lachezar Bozhkov

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// Unambiguous, recommended

x + (y / 100)

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int squarePerimeter = 17;

double squareSide = squarePerimeter / 4.0;

double squareArea = squareSide * squareSide;

System.out.println(squareSide); // 4.25

System.out.println(squareArea); // 18.0625

int a = 5;

int b = 4;

System.out.println(a + b); // 9

System.out.println(a + b++); // 9


System.out.println(a + (++b)); // 11


System.out.println(14 / a); // 2

System.out.println(14 % a); // 4

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x

y

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boolean a = true;

boolean b = false;

System.out.println(a && b); // false

System.out.println(a || b); // true

System.out.println(!b); // true

System.out.println(b || true); // true

System.out.println((5>7) ^ (a==b)); // false

:

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!(a || b) == (!a && !b)

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+ (String). , . String, , String, String.

, :

String first = "Star";

String second = "Craft";

System.out.println(first + second); // StarCraft

String output = first + second + " ";

int number = 2;

System.out.println(output + number);

// StarCraft 2

String . println(), . . output. output 2 ( number) . String, .

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- ( y)); // true

System.out.println("x < y : " + (x < y)); // false

System.out.println("x >= y : " + (x >= y)); // true

System.out.println("x b" : "b 0); // Check the loop condition

System.out.println("n! = " + factorial);

n=7:

n = 7

n! = 5040

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[N...M]

[NM]. num. num. product, num 1 num m.

Scanner input = new Scanner(System.in);

// Read the end values of the interval n...m from the console

int n = input.nextInt();

int m = input.nextInt();

int num = n;

long product = 1;

do {

product *= num;

num++;

} while (num 1 2 3 4 5n=6->1 2 3 4 5 6

1 2 3 41 2 3 4 5

1 2 31 2 3 4

1 21 2 3

11 2

1

:

Triangle.java

import java.util.Scanner;

public class Triangle {

public static void main(String[] args) {

// Entering the value of the variable n

System.out.print("n = ");



System.out.println();

// Printing the upper part of the triangle

for (int line = 1; line = 1; line--) {

printLine(1, line);

}

}

private static void printLine(int start, int end) {

for (int i = start; i = 37) {

System.out.println("You are ill!");

}

input.close();

}

}

, , . , , . , , -, , , . convertFahrenheitToCelsius(), temperatureF, double, . Java.

, , , main() .

Scanner, , "Enter your body temperature in Fahrenheit degrees".

convertFahrenheitToCelsius(), temperature.

printf() System.out, "Your body temperature in Celsius degrees is X", X temperature.

, if, - 37 , , .

:

Enter your body temperature in Fahrenheit degrees:

100

Your body temperature in Celsius degrees is 37,777778.

You are ill!

, , ( "What time is it?"). , , . , , "The time is HH:mm now.", , mm . , "Incorrect time!".

, , :

.

.

.

, , , .. . , 0 23 , 0 59 . ( ) , , .

:

DataValidation.java


public class DataValidation {



System.out.println("What time is it?");

System.out.print("Hours: ");

int hours = input.nextInt();

System.out.print("Minutes: ");

int minutes = input.nextInt();

boolean isValidTime =

validateHours(hours) && validateMinutes(minutes);

if (isValidTime) {

System.out.printf(

"The time is %d:%d now.%n", hours, minutes);

} else {

System.out.println("Incorrect time!");

}

}

public static boolean validateHours(int hours) {

boolean result = (hours >= 0) && (hours < 24);

return result;

}

public static boolean validateMinutes(int minutes) {

boolean result = (minutes >= 0) && (minutes = 0) && (hours < 24);

return result;

}

, , . validateMinutes(), , boolean. , -, 0 59 , true, false:

public static boolean validateMinutes(int minutes) {

boolean result = (minutes >= 0) && (minutes numbers[j]) {

int tempVar = numbers[i];

numbers[i] = numbers[j];

numbers[j] = tempVar;

}

}

} // End of the sorting logic

return numbers;

}

printNumbers(int...) :

SortingEngine.java

public class SortingEngine {

public static int[] sort(int... numbers) {

// The sorting logic:

for (int i = 0; i < numbers.length - 1; i++) {

// Loop that is operating over the un-sorted part of

// the array

for (int j = i + 1; j < numbers.length; j++) {

// Swapping the values

if (numbers[i] > numbers[j]) {

int temp = numbers[i];

numbers[i] = numbers[j];

numbers[j] = temp;

}

}

} // End of the sorting logic

return numbers;

}

public static void printNumbers(int... numbers) {

for (int i = 0; i < numbers.length; i++) {

System.out.printf("%d", numbers[i]);

if (i < (numbers.length - 1)) {

System.out.print(", ");

}

}

}


int[] numbers = sort(10, 3, 5, -1, 0, 12, 8);

printNumbers(numbers);

}

}

, , , :

-1, 0, 3, 5, 8, 10, 12

" " , , . :

, . strong cohesion. , - -. !

, . , , sortNumbers(), number() processing() method2(). , - .

( , ), findSmallestElement() sort(int[] arr) readInputData().

Java . camelCase, .. , , .

, , . . , , . . " ".

(- , ). , , , , ( ). loose coupling.

, - " ". , , - "" .

, , , , . , , , , , . , , .

1. , "Hello, !" ( "Hello, Peter!"). , .

2. getMax() (int) , - . , - , getMax().

3. , . : 512 "two"; 1024 "four".

4. , . , .

5. , , , -, - .

6. , , - , -1, .

7. , . 256, 652.

8. , n! n [1..100].

9. , :

.

.

a * x + b = 0.

.

, , .

:

.

.

a 0.

10. , .

1. String.

2. Max(a, b, c) = Max(Max(a, b), c).

3. 10 switch .

4. (int[]) (int).

5. , .

6. , .

7. :

: num. num 0 (num % 10) num 10.

: String for .

8. , 100! long. , . 512 {2, 1, 5}. , ( ).

9. . (1 - , 2 - , 3 - ) 1 3.

10. , .

330 Java

9. 329

()

,

:

( Java, C# C++)

:





,

!

350



10.

...

. , . , . .

?

, . .

, .

, . .

. :

1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144,

. 1, .. :

F1 = F2 = 1

Fi = Fi-1 + Fi-2 ( i > 2)

, n- :

public static long fib(int n) {

if (n 0

. . , .

0! = 1

1! = 1 = 1.1 = 1.0!

2! = 2.1 = 2.1!

3! = 3.2.1 = 3.2!

4! = 4.3.2.1 = 4.3!

5! = 5.4.3.2.1 = 5.4!

:

n! = n.(n-1)!

n = 0, 1.

, n-1 n. , , 0 n .

, .

public static long factorial(int n) {

// The bottom of the recursion

if (n == 0) {

return 1;

}

// Recursive call: the method calls itself

else {

return n * factorial(n - 1);

}

}

, , , :

RecursiveFactorial.java


public class RecursiveFactorial {



System.out.print("n = ");


long factorial = factorial(n);

System.out.printf("%d! = %d%n", n, factorial);

input.close();

}


// The bottom of the recursion

if (n == 0) {

return 1;

}

// Recursive call: the method calls itself

else {

return n * factorial(n - 1);

}

}

}

, 5 n:

n = 5

5! = 120

, , , - .

, , , () .

, , -:


long result = 1;

for (int i = 1; i at Junk.b(Junk.java:18)

at Junk.a(Junk.java:12)

at Junk.main(Junk.java:4) ( -)

"" -. .

Error

Error ( ). , . Error.

Error Throwable, : stack trace , getMessage(), printStackTrace() getStackTrace() , getCause().

OutOfMemoryError, , .

Exception

. checked . Exception, Throwable. checked stack trace, Throwable.

( ).

IOException, - . .

RuntimeException

. unchecked . RuntimeException, Exception, Throwable. unchecked Throwable (stack trace, message, cause .). .

throws

, . , , . . , , throws. :

public static void readFile(String fileName)

throws FileNotFoundException, IOException {

}

, - FileNotFoundException IOException. FileNotFoundException , IOException. - . - Runtime , .

. , , , throws FileNotFoundException, IOException.

public static void readFile(String fileName)


FileInputStream fis = null;

fis = new FileInputStream(fileName);

BufferedReader in = new BufferedReader(

new InputStreamReader(fis));

String tmp = null;

while ((tmp = in.readLine()) != null) {

System.out.println(tmp);

}

in.close();

fis.close();

}

, . - , , . , , . - throws .

(GUI) , . . , .

:

, , . .

, main() , ( ) .

?

checked -. . -, checked. , -, , , -. , , , RuntimeException -. - - A-. , (nested exceptions).

main()

main() 1.4 JDK . . Java 5 main() , :

public static void main(String a[])


readFile("C:\\tools\\eclipse\\eclipse.ini");

}

main() stack trace (System.err). , main() , .

- . . () . readFile() :


try {

readFile("C:\\tools\\eclipse\\eclipse.ini");

} catch (IOException e) {

e.printStackTrace();

}

}

public static void readFile(String fileName) throws IOException{

try {

FileInputStreamfis = new FileInputStream(fileName);

BufferedReader in = new BufferedReader(

new InputStreamReader(fis));

String tmp = null;

while ((tmp = in.readLine()) != null) {

System.out.println(tmp);

}

} catch (FileNotFoundException e) {

System.out.println("The file \"" + fileName +

"\" does not exist! Unable to read it.");

}

}

readFile() main() . readFile() FileNotFoundException, IOException main() .

main() FileNotFoundException readFile(). main() .

- .

try-finally

try finally. finally try , try . finally return.

finally , try !

finally :

try {

Some code that could or could not cause an exception

} finally {

// Code here will allways execute

}

try finally catch. catch finally .

try {

some code

} catch (...) {

// Code handling an exception

} catch (...) {

// Code handling another exception

} finally {

// This code will allways execute

}

finally . , return, continue, break .

, , . - try- finally , . :

public static void readFile(String fileName) throws IOException{

FileInputStream fis = new FileInputStream(fileName);

BufferedReader in =

new BufferedReader(new InputStreamReader(fis));

// Using the streams here

in.close();

fis.close();

}

FileInputStream BufferedReader. . , :

.

.

.

return.

.

, . , . , continue break, .

try-finally. , .

:

FileInputStream fis = null;

try {

fis = new FileInputStream("fileName.txt");

// Using "fis" here ...

} finally {

// Always cl

Documents

Introduction to Programming with Java · Web view957. Глава 5. Условни конструкции. 215. 168. Въведение в програмирането с Java