Five useful ways to sorting in java

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 elements = new ArrayList();
        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 holidays = new ArrayList();
            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());
	}
	}
	}

view raw SortDemo.java hosted with ❤ by GitHub