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Resolución de ejercicios de métodos

a)

import java.io.*;

public class PrimoPar {

  public static boolean par(int num)
  {
    if (num % 2 == 0)
    {
      return true;
    }
    else
    {
      return false;
    }
  }

  public static boolean perfecto(int num) {

    int sum = 0;
    for(int i = 1; i < num; i++)
    {
      if(num % i == 0)
      {
        sum += i;
      }
    }

    if (sum == num)
    {
      return true;
    }
    else
    {
      return false;
    }
  }

  public static void main(String[] args) throws IOException {

    int a,b,cont = 0;

    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

    System.out.print("a : ");
    a = Integer.parseInt(in.readLine());

    System.out.print("b : ");
    b = Integer.parseInt(in.readLine());

    for(int i = a; i <= b; i++)
    {
      if ( par(i) && perfecto(i) )
      {
        System.out.print(i + "\t");
        cont++;
      }
    }

    System.out.println("\n\nExisten " + cont + " numeros que cumplen la condicion");

  }
}

b)

import java.io.*;
public class SumatoriaEsp {

  public static boolean primo(int num) {

    int cont = 0;
    for(int i =1; i < num; i++)
    {
      if (num % i == 0) { cont++; }
    }

    if (cont < 2) { return true; }
    else { return false; }

  }

  public static boolean multiploEspecial(int num) {

    boolean aux = false;

    if (num % 5 == 0 || num % 7 == 0) { aux = !aux;  }

    return aux;
  }

  /* un metodo puede ser llamado desde otro método */

  public static int sumatoria(int a, int b) {

    int sum = 0;
    for(int i = a; i <= b; i++)
    {
      if ( primo(i) ) { sum += i*i; }
      if ( multiploEspecial(i) ) { sum -= i;}

      /* System.out.println("i : " + i + " sum : " + sum); */
    }

    return sum;
  }


  public static void main(String[] args) throws IOException {

    int a , b , s = 0;

     BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

     System.out.print("a : ");
     a = Integer.parseInt(in.readLine());

     System.out.print("b : ");
     b = Integer.parseInt(in.readLine());

     s = sumatoria(a,b);

     System.out.print("\n\nEl valor de la sumatoria de " + a + " hasta " + b + " es : " + s );
  }
}