MultiComparator

Quando você escreve um SQL para retornar informações do banco de dados de forma ordenada por vários campos, você escreve algo mais ou menos assim:

ORDER BY nome, idade, codigo

E em Java como você reproduz esta funcionaliade?

Eu faço assim ó :D

/**
 * You can easily combine the results from several Comparators for an object
 * class into one Comparator.
 * 

 *
 * You have the multi-comparator, and individual comparators for all the fields,
 * you can create a comparator that has any properties you want. For example, to
 * sort on EmployeeID, Name, and Age, in that order, you would do this:
 * 

 *
 * 

 * MultiComparator mc = new MultiComparator();
 * mc.add(new EmployeeIdComparator(MyENum.ASC));
 * mc.add(new EmployeeNameComparator(MyENum.ASC));
 * mc.add(new EmployeeAgeComparator(MyENum.DESC));
 * Collections.sort(list, mc);
 *
 */
public class MultiComparator implements Comparator < book > {
 private List<comparator < book > comparatorList;

 public MultiComparator() {
  comparatorList = new ArrayList<comparator<book>>();
 }

 public void addComparator(Comparator<book> c) {
  comparatorList.add(c);
 }

 public void removeComparator(Comparator<object> c) {
  comparatorList.remove(c);
 }

 public int compare(Book obj1, Book obj2) {
  int result = 0;
  for (Comparator<book> c : comparatorList) {
   result = c.compare(obj1, obj2);

   if (result != 0) {
    break;
   }
  }
  return result;
 }
}

Calculando diferença entre datas

Hoje coloco aqui disponível a todos um exemplo de classe que utilizo para calcular diferença entre datas

package com.wealthsystems.sim.utils.date;

import java.util.Date;

/**
 * Calculate difference of dates
 * 
 * @author Clayton
 * 
 */
public class DateDiff {
    /**
     * Get difference in milliseconds
     * 
     * @param data1
     *            data mais antiga (natal)
     * @param data2
     *            data mais nova (ano novo)
     * @return
     */
    public static long inMiliseconds(Date data1, Date data2) {
 long diffMillis = data2.getTime() - data1.getTime();
 return diffMillis;
    }

    /**
     * Get difference in seconds
     * 
     * @param data1
     * @param data2
     * @return
     */
    public static long inSeconds(Date data1, Date data2) {
 long diffSecs = inMiliseconds(data1, data2) / (1000); // 604800
 return diffSecs;
    }

    /**
     * Get difference in minutes
     * 
     * @param data1
     * @param data2
     * @return
     */
    public static long inMinutes(Date data1, Date data2) {
 long diffMins = inMiliseconds(data1, data2) / (60 * 1000); // 10080
 return diffMins;
    }

    /**
     * Get difference in hours
     * 
     * @param data1
     * @param data2
     * @return
     */
    public static long inHours(Date data1, Date data2) {
 long diffHours = inMiliseconds(data1, data2) / (60 * 60 * 1000); // 168
 return diffHours;
    }

    /**
     * Get difference in days
     * 
     * @param data1
     * @param data2
     * @return
     */
    public static long inDays(Date data1, Date data2) {
 long diffDays = inMiliseconds(data1, data2) / (24 * 60 * 60 * 1000); // 7
 return diffDays;
    }

    public static String toStringInHour(Date data1, Date data2) {
 long hour = DateDiff.inHours(data1, data2);
 long minutes = DateDiff.inMinutes(data1, data2);
 long seconds = DateDiff.inSeconds(data1, data2);

 StringBuffer sb = new StringBuffer();
 sb.append(hour);
 sb.append(":");
 sb.append(minutes - (hour * 60));
 sb.append(":");
 sb.append(seconds - (minutes * 60));

 return sb.toString();
    }
}