A rapid overview of java sorting :
 
 
 
 
 
 
 
 
 
 

normal sort of list :

 private static List VEGETABLES = Arrays.asList("apple", "cocumbers", "blackberry");
 Collections.sort(VEGETABLES);

 output: apple, blackberry, cocumbers 
 

Reverse sorting:

 private static List VEGETABLES = Arrays.asList("apple", "cocumbers", "blackberry");
 Collections.sort(VEGETABLES, Collections.reverseOrder());
 output: cocumbers, blackberry, apple
 

with custom comparator:

 private class StringComparator implements Comparator {
 public int compare(Object o1, Object o2) {
 String so1 = (String) o1;
 String so2 = (String) o2;
 return so1.compareTo(so2);
 }
 }
 private static List VEGETABLES = Arrays.asList("apple", "cocumbers", "blackberry");
 Collections.sort(VEGETABLES, new StringComparator());
 output: apple, blackberry, cocumbers
 

Elements sorting:

 private class Element implements Comparable {
 private String name;
 private Double atomicMass;
 
 @Override
 public String toString() {
 final StringBuilder sb = new StringBuilder();
 sb.append("Element");
 sb.append("{name='").append(name).append('\'');
 sb.append(", atomicMass=").append(atomicMass);
 sb.append('}');
 return sb.toString();
 }
 
 public String getName() {
 return name;
 }
 
 public void setName(String name) {
 this.name = name;
 }
 
 public Double getAtomicMass() {
 return atomicMass;
 }
 
 public void setAtomicMass(Double atomicMass) {
 this.atomicMass = atomicMass;
 }
 
 public Element(String name, String mass, double atomicMass) {
 this.name = name;
 this.atomicMass = atomicMass;
 }
 
 public int compareTo(Element o) {
 return this.getAtomicMass().compareTo(o.getAtomicMass());
 }
 }
 
 ArrayList<Element> elements = new ArrayList<Element>();
 elements.add(new Element("Hydrogen", "H", 1.00794)); // Hydrogen 1.00794 amu Atomic Mass
 elements.add(new Element("Iron", "Fe", 55.845));
 elements.add(new Element("Lithium", "Li", 6.941));
 elements.add(new Element("Lead", "Pb", 207.2));
 elements.add(new Element("Magnesium", "Mg", 24.305));
 Collections.sort(elements); // Sort by Element
 

output:

 Element{name='Hydrogen', atomicMass=1.00794}
 Element{name='Lithium', atomicMass=6.941}
 Element{name='Magnesium', atomicMass=24.305}
 Element{name='Iron', atomicMass=55.845}
 Element{name='Lead', atomicMass=207.2}
 

Chronological sorting:

 SimpleDateFormat formatter = new SimpleDateFormat("MMMM dd, yyyy", Locale.US);
 try {
 ArrayList<Date> holidays = new ArrayList<Date>();
 holidays.add(formatter.parse("May 31, 2010")); // Memorial Day
 holidays.add(formatter.parse("July 4, 2010")); // Independence Day
 holidays.add(formatter.parse("February 15, 2010")); // Presidents Day
 holidays.add(formatter.parse("September 6, 2010")); // Labor Day
 holidays.add(formatter.parse("December 24, 2010")); // Thanksgiving Day
 holidays.add(formatter.parse("July 5, 2010")); // federal employees extra day off for July 4th
 holidays.add(formatter.parse("January 18, 2010")); // Martin Luther King Day
 holidays.add(formatter.parse("November 25, 2010")); // federal employees extra day off for Christmas
 holidays.add(formatter.parse("October 11, 2010")); // Columbus Day
 holidays.add(formatter.parse("December 25, 2010")); // Christmas Day
 holidays.add(formatter.parse("January 1, 2010")); // New Year's Day
 Collections.sort(holidays); // Native sort for Date is chronological
 
 } catch (ParseException e) {
 e.printStackTrace();
 }
 

output:

 sorted:[Fri Jan 01 00:00:00 CET 2010, Mon Jan 18 00:00:00 CET 2010, Mon Feb 15 00:00:00 CET 2010, Mon May 31 00:00:00 CEST 2010, Sun Jul 04 00:00:00 CEST 2010, Mon Jul 05 00:00:00 CEST 2010, Mon Sep 06 00:00:00 CEST 2010, Mon Oct 11 00:00:00 CEST 2010, Thu Nov 25 00:00:00 CET 2010, Fri Dec 24 00:00:00 CET 2010, Sat Dec 25 00:00:00 CET 2010]
 

You can view the complete simple class below:

 
package com.tommyalf.personal.sorting;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;

/**
* Created by IntelliJ IDEA.
* User: tommyalf
* Date: 1-dic-2010
* Time: 22.40.49
*/
public class SortDemo {
 private static List VEGETABLES = Arrays.asList("apple", "cocumbers", "blackberry");;


 public static void main(String args[]) {
 SortDemo sd = new SortDemo();
 sd.normalSort();
 sd.reverseSort();
 sd.stringComparator();
 sd.elementsSort();
 sd.chronologicalSort();
 }

 private void chronologicalSort() {
 SimpleDateFormat formatter = new SimpleDateFormat("MMMM dd, yyyy", Locale.US);
 try {
 ArrayList<Date> holidays = new ArrayList<Date>();
 holidays.add(formatter.parse("May 31, 2010")); // Memorial Day
 holidays.add(formatter.parse("July 4, 2010")); // Independence Day
 holidays.add(formatter.parse("February 15, 2010")); // Presidents Day
 holidays.add(formatter.parse("September 6, 2010")); // Labor Day
 holidays.add(formatter.parse("December 24, 2010")); // Thanksgiving Day
 holidays.add(formatter.parse("July 5, 2010")); // federal employees extra day off for July 4th
 holidays.add(formatter.parse("January 18, 2010")); // Martin Luther King Day
 holidays.add(formatter.parse("November 25, 2010")); // federal employees extra day off for Christmas
 holidays.add(formatter.parse("October 11, 2010")); // Columbus Day
 holidays.add(formatter.parse("December 25, 2010")); // Christmas Day
 holidays.add(formatter.parse("January 1, 2010")); // New Year's Day
 System.out.println("before sort:" + holidays);
 Collections.sort(holidays); // Native sort for Date is chronological
 System.out.println("sorted:" + holidays);
 } catch (ParseException e) {
 e.printStackTrace();
 }
 }

 private void elementsSort() {
 ArrayList<Element> elements = new ArrayList<Element>();
 elements.add(new Element("Hydrogen", "H", 1.00794)); // Hydrogen 1.00794 amu Atomic Mass
 elements.add(new Element("Iron", "Fe", 55.845));
 elements.add(new Element("Lithium", "Li", 6.941));
 elements.add(new Element("Lead", "Pb", 207.2));
 elements.add(new Element("Magnesium", "Mg", 24.305));
 Collections.sort(elements); // Sort by Element
 System.out.print("Elements sort by atomicMass value:");
 for ( Element e : elements ) {
 System.out.println(e);
 }
 }

 private void stringComparator() {
 Collections.sort(VEGETABLES, new StringComparator());
 System.out.print("StringComparator:");
 printList(VEGETABLES);
 }

 private void reverseSort() {
 Collections.sort(VEGETABLES, Collections.reverseOrder());
 System.out.print("ReverseSort:");
 printList(VEGETABLES);
 }

 private void normalSort() {
 Collections.sort(VEGETABLES);
 System.out.print("NormalSort:");
 printList(VEGETABLES);
 }

 private void printList(List vegetables) {
 for (int i = 0, n = vegetables.size(); i < n; i++) {
 if (i != 0) {
 System.out.print(", ");
 }
 System.out.print(VEGETABLES.get(i));
 }
 System.out.println();
 }

 private class StringComparator implements Comparator {
 public int compare(Object o1, Object o2) {
 String so1 = (String) o1;
 String so2 = (String) o2;
 return so1.compareTo(so2);
 }
 }

 private class Element implements Comparable<Element> {
 private String name;
 private Double atomicMass;

 @Override
 public String toString() {
 final StringBuilder sb = new StringBuilder();
 sb.append("Element");
 sb.append("{name='").append(name).append('\'');
 sb.append(", atomicMass=").append(atomicMass);
 sb.append('}');
 return sb.toString();
 }

 public String getName() {
 return name;
 }

 public void setName(String name) {
 this.name = name;
 }

 public Double getAtomicMass() {
 return atomicMass;
 }

 public void setAtomicMass(Double atomicMass) {
 this.atomicMass = atomicMass;
 }

 public Element(String name, String mass, double atomicMass) {
 this.name = name;
 this.atomicMass = atomicMass;
 }


 public int compareTo(Element o) {
 return this.getAtomicMass().compareTo(o.getAtomicMass());
 }
 }
}
 

Reference: Five useful ways to sorting in java from our JCG partner Tommy Alf at the Tommy Alf – blog blog.