SE_21_Lesson_5: Methods

 1. Structure of a method

2. Method signature:

Method signature consists of method name and its parameters.

There can not be two methods with same signature.

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package org.example;

public class Main {
    public static void main(String[] args) {
        byte b = 3;
        foo(3);
    }

    public static void foo(short i) {
        System.out.println("in short");
    }

    public static void foo(int i) {
        System.out.println("in int");
    }

    public static void foo(long i) {
        System.out.println("in long");
    }
}

*** Advantage of using Variable arguments

public static double average(double a, double b) {
    return (a + b) / 2;
}

public static double average(double a, double b, double c) {
    return (a + b + c) / 3;
}

public static double averageArray(double[] arr) {
    double sum = 0;
    for(int i = 0; i < arr.length; i++) {
        sum += arr[i];
    }
    return sum / arr.length;
}

public static double average(double... arr) {
    double sum = 0;
    for(int i = 0; i < arr.length; i++) {
        sum += arr[i];
    }
    return sum / arr.length;
}

Problem with variable arguments

package org.example;

public class Main {
    public static void main(String[] args) {
        foo(1, 2, 3);
    }

    public static void foo(int... args) {
        System.out.println(args);
    }

    public static void foo(int i, int... args) {
        System.out.println(i);
        System.out.println(args);
    }

    public static void foo(int i, int j, int... args) {
        System.out.println(i);
        System.out.println(j);
        System.out.println(args);
    }
}

***Recursion

1) Simple recursion

public static void foo(int n) {
    System.out.println(n);
    foo(n);
}

2) Print numbers in descending order

public static void foo(int n) {
    if(n == 0) {
        System.out.println(n);
        return;
    }
    System.out.println(n);
    foo(n - 1);
}

3) Print numbers in ascending order

public static void foo(int n) {
    if(n == 0) {
        System.out.println(n);
        return;
    }
    foo(n - 1);
    System.out.println(n);
}

4) Print digits of number

public static void foo(int n) {
    if(n == 0) return;
    System.out.println(n % 10);
    foo(n / 10);
}

public static void foo(int n) {
    if(n == 0) return;
    foo(n / 10);
    System.out.println(n % 10);
}

5) Finding factorial

public static int foo(int n) {
    if (n == 0) return 1;
    else {
        return n * foo(n - 1);
    }
}

public static int foo(int n) {
    if (n == 0) return 1;
    else {
        int prev = foo(n - 1);
        int result = n;
        result *= prev;
        return result;
    }
}

6) Fibonacci number

public static int foo(int n) {
    if (n == 0 || n == 1) return n;
    else {
        return foo(n - 1) + foo(n - 2);
    }
}