تصميم الدوال

public class OverloadedAdd {
    static int add(int a, int b) {
        return a + b;
    }

    static double add(double a, double b) {
        return a + b;
    }

    static int add(int a, int b, int c) {
        return a + b + c;
    }

    public static void main(String[] args) {
        System.out.println(add(3, 4));
        System.out.println(add(3.5, 4.0));
        System.out.println(add(1, 2, 3));
    }
}

7
7.5
6

public class AddTenReturn {
    static int addTen(int n) {
        n = n + 10;
        return n;
    }

    public static void main(String[] args) {
        int x = 5;
        x = addTen(x);
        System.out.println(x);
    }
}

15

public class FailedSwap {
    static void swap(int a, int b) {
        int temp = a;
        a = b;
        b = temp;
        System.out.println("in swap: a = " + a + ", b = " + b);
    }

    public static void main(String[] args) {
        int a = 5;
        int b = 9;
        swap(a, b);
        System.out.println("in main: a = " + a + ", b = " + b);
    }
}

in swap: a = 9, b = 5
in main: a = 5, b = 9

import java.util.Scanner;

public class MenuBefore {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int choice;
        do {
            System.out.println("1) Add");
            System.out.println("2) Even or odd");
            System.out.println("0) Exit");
            System.out.print("Choice: ");
            choice = input.nextInt();
            if (choice == 1) {
                System.out.print("a: ");
                int a = input.nextInt();
                System.out.print("b: ");
                int b = input.nextInt();
                System.out.println("Sum = " + (a + b));
            } else if (choice == 2) {
                System.out.print("n: ");
                int n = input.nextInt();
                if (n % 2 == 0) {
                    System.out.println("even");
                } else {
                    System.out.println("odd");
                }
            } else if (choice != 0) {
                System.out.println("Unknown choice");
            }
        } while (choice != 0);
        System.out.println("Bye");
    }
}

1) Add
2) Even or odd
0) Exit
Choice: a: b: Sum = 7
1) Add
2) Even or odd
0) Exit
Choice: n: odd
1) Add
2) Even or odd
0) Exit
Choice: Unknown choice
1) Add
2) Even or odd
0) Exit
Choice: Bye

import java.util.Scanner;

public class MenuAfter {
    static void printMenu() {
        System.out.println("1) Add");
        System.out.println("2) Even or odd");
        System.out.println("0) Exit");
    }

    static int readInt(Scanner input, String prompt) {
        System.out.print(prompt);
        return input.nextInt();
    }

    static boolean isEven(int n) {
        return n % 2 == 0;
    }

    static void handleAdd(Scanner input) {
        int a = readInt(input, "a: ");
        int b = readInt(input, "b: ");
        System.out.println("Sum = " + (a + b));
    }

    static void handleEvenOdd(Scanner input) {
        int n = readInt(input, "n: ");
        if (isEven(n)) {
            System.out.println("even");
        } else {
            System.out.println("odd");
        }
    }

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int choice;
        do {
            printMenu();
            choice = readInt(input, "Choice: ");
            if (choice == 1) {
                handleAdd(input);
            } else if (choice == 2) {
                handleEvenOdd(input);
            } else if (choice != 0) {
                System.out.println("Unknown choice");
            }
        } while (choice != 0);
        System.out.println("Bye");
    }
}

1) Add
2) Even or odd
0) Exit
Choice: a: b: Sum = 7
1) Add
2) Even or odd
0) Exit
Choice: n: odd
1) Add
2) Even or odd
0) Exit
Choice: Unknown choice
1) Add
2) Even or odd
0) Exit
Choice: Bye

public class CountDown {
    static void countDown(int n) {
        if (n == 0) {
            System.out.println("Go!");
        } else {
            System.out.println(n);
            countDown(n - 1);
        }
    }

    public static void main(String[] args) {
        countDown(3);
    }
}

3
2
1
Go!

public class Factorial {
    static int factorial(int n) {
        if (n <= 1) {
            return 1;
        }
        int smaller = factorial(n - 1);
        return n * smaller;
    }

    public static void main(String[] args) {
        System.out.println(factorial(4));
    }
}

24

public class PrimeList {
    static boolean isPrime(int n) {
        if (n < 2) {
            return false;
        }
        for (int d = 2; d * d <= n; d++) {
            if (n % d == 0) {
                return false;
            }
        }
        return true;
    }

    public static void main(String[] args) {
        for (int i = 1; i <= 20; i++) {
            if (isPrime(i)) {
                System.out.print(i + " ");
            }
        }
        System.out.println();
    }
}

2 3 5 7 11 13 17 19

public class MathTools {
    static int gcd(int a, int b) {
        while (b != 0) {
            int remainder = a % b;
            a = b;
            b = remainder;
        }
        return a;
    }

    static long power(int base, int exponent) {
        long result = 1;
        for (int i = 0; i < exponent; i++) {
            result = result * base;
        }
        return result;
    }

    public static void main(String[] args) {
        int x = 84;
        System.out.println(gcd(x, 36));
        System.out.println(x);
        System.out.println(power(2, 10));
        System.out.println(power(2, 40));
        System.out.println(power(7, 0));
    }
}

12
84
1024
1099511627776
1