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.
