Comparator Examples

Comparator Example :

Sort By Frequency

	package com.tvidushi.arrays;
	import java.util.Arrays;
	import java.util.Map;
	import java.util.TreeMap;
	public class SortByFrequency {
	public static void main(String[] args) {
	sortByFrequency(new int[] {3,3,4,2,4,4, 2, 4, 4});
	// Sort array based on count of occurrences in ascending order
	}
	public static void sortByFrequency(int[] in) {
	TreeMap<Integer, Integer> map = new TreeMap();
	int[] temp = new int[in.length];
	for(int i =0;i<in.length;i++){
	if(map.containsKey(in[i])){
	int count = map.get(in[i]);
	map.put(in[i], count+1);
	}else{
	map.put(in[i], 1);
	}
	}
	Map<Integer, Integer>rm = map.descendingMap();
	for(Map.Entry<Integer, Integer> entry : rm.entrySet()){
	int frequency = entry.getValue();
	int value = entry.getKey();
	//System.out.println(" frequency "+frequency+" value "+value);
	//System.out.println();
	for(int i=0;i<frequency;i++){
	temp[i] = value;
	System.out.print(""+temp[i]);
	}
	}
	}

view raw SortByFequency.java hosted with ❤ by GitHub

Sorting By Comparators in java 8
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	package com.tvidushi.java8.sorted;
	import java.util.Arrays;
	import java.util.Collections;
	import java.util.Comparator;
	import java.util.List;
	import java.util.Optional;
	public class SortingMadeEasy {
	public static List<Integer> numbers = Arrays.asList(11, 23, 13, 67,46, 51, 36, 71, 81, 19, 101);
	public static List<String> names = Arrays.asList("Ravish", "Vidushi", "Russel", "Peter","Vir", "Das","Ashi");
	public static void main(String[] args) {
	natrualOrder_num();
	natrualOrder_str();
	sortInReverseOrder();
	sortAsc();
	sortDesc() ;
	}
	public static void natrualOrder_num() {
	Optional.ofNullable(numbers).ifPresent(list -> list.sort(Comparator.naturalOrder()));
	System.out.println(numbers);
	}
	public static void natrualOrder_str() {
	names.sort(Comparator.naturalOrder());
	//Optional.ofNullable(names).ifPresent(list -> list.sort(Comparator.naturalOrder()));
	System.out.println(names);
	}
	public static void sortInReverseOrder() {
	List<String> names = Arrays.asList("peter", "anna", "mike", "xenia");
	names.sort(Collections.reverseOrder());
	System.out.println(names);
	}
	// lambda ways
	public static void sortELement_3() {
	System.out.println("Sorting a string array in reverse order");
	List<String> names = Arrays.asList("peter", "banna", "mike", "xenia");
	Collections.sort(names, (String a, String b) -> {
	return b.compareTo(a);
	});
	System.out.println(names);
	}
	public static void sortAsc() {
	System.out.println("Sorting a string array in natural order");
	List<String> names2 = Arrays.asList("peter", null, "anna", "mike", "xenia");
	names2.sort(Comparator.nullsLast(String::compareTo));
	System.out.println(" _____"+names2);
	}
	// normal way
	public static void sortDesc() {
	System.out.println("Sorting a string array in reverse order");
	List<String> names = Arrays.asList("peter", "anna", "mike", "xenia");
	Collections.sort(names, new Comparator<String>() {
	@Override
	public int compare(String a, String b) {
	return b.compareTo(a); // This desending order of sorting
	}
	});
	System.out.println(names);
	}
	}

view raw SortingMadeEasy.java hosted with ❤ by GitHub

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	public class SortUsingLastNames {
	public void sortLast(ArrayList<String> al) {
	Collections.sort(al, new Comparator<String>() {
	public int compare(String o1, String o2) {
	String[] split1 = o1.split(" ");
	String[] split2 = o2.split(" ");
	String lastName1 = split1[1];
	String lastName2 = split2[1];
	if (lastName1.compareTo(lastName2) > 0) {
	return 1;
	} else {
	return -1;
	}
	}
	});
	System.out.println(al);
	}
	public static void main(String[] args) {
	ArrayList<String> al = new ArrayList<String>();
	al.add("Daenerys Targaryen");
	al.add("Jon Show");
	al.add("Tyrion Lannister");
	al.add("Joffrey Baratheon");
	SortUsingLastNames i = new SortUsingLastNames();
	System.out.println("Sorted using Last Name");
	i.sortLast(al);
	}
	}

view raw SortUsingLastNames.java hosted with ❤ by GitHub

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