Java 8 - Comment trier une carte

sorting

Exemples Java 8Stream pour trier unMap, par clés ou par valeurs.

1. Explication rapide

Étapes pour trier une carte dans Java 8.

Convertir une carte en un flux
Trier
Récupérez et retournez un nouveauLinkedHashMap (gardez la commande)

Map result = map.entrySet().stream()
    .sorted(Map.Entry.comparingByKey())
    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
    (oldValue, newValue) -> oldValue, LinkedHashMap::new));

P.S By default, Collectors.toMap will returns a `HashMap`

2. Trier par clés

SortByKeyExample.java

package com.example.test;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.stream.Collectors;

public class SortByKeyExample {

    public static void main(String[] argv) {

        Map unsortMap = new HashMap<>();
        unsortMap.put("z", 10);
        unsortMap.put("b", 5);
        unsortMap.put("a", 6);
        unsortMap.put("c", 20);
        unsortMap.put("d", 1);
        unsortMap.put("e", 7);
        unsortMap.put("y", 8);
        unsortMap.put("n", 99);
        unsortMap.put("g", 50);
        unsortMap.put("m", 2);
        unsortMap.put("f", 9);

        System.out.println("Original...");
        System.out.println(unsortMap);

        // sort by keys, a,b,c..., and return a new LinkedHashMap
        // toMap() will returns HashMap by default, we need LinkedHashMap to keep the order.
        Map result = unsortMap.entrySet().stream()
                .sorted(Map.Entry.comparingByKey())
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));


        // Not Recommend, but it works.
        //Alternative way to sort a Map by keys, and put it into the "result" map
        Map result2 = new LinkedHashMap<>();
        unsortMap.entrySet().stream()
                .sorted(Map.Entry.comparingByKey())
                .forEachOrdered(x -> result2.put(x.getKey(), x.getValue()));

        System.out.println("Sorted...");
        System.out.println(result);
        System.out.println(result2);

    }

}

Sortie

Original...
{a=6, b=5, c=20, d=1, e=7, f=9, g=50, y=8, z=10, m=2, n=99}

Sorted...
{a=6, b=5, c=20, d=1, e=7, f=9, g=50, m=2, n=99, y=8, z=10}
{a=6, b=5, c=20, d=1, e=7, f=9, g=50, m=2, n=99, y=8, z=10}

3. Trier par valeurs

SortByValueExample.java

package com.example.test;

package com.example;

import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.stream.Collectors;

public class SortByValueExample {

    public static void main(String[] argv) {

        Map unsortMap = new HashMap<>();
        unsortMap.put("z", 10);
        unsortMap.put("b", 5);
        unsortMap.put("a", 6);
        unsortMap.put("c", 20);
        unsortMap.put("d", 1);
        unsortMap.put("e", 7);
        unsortMap.put("y", 8);
        unsortMap.put("n", 99);
        unsortMap.put("g", 50);
        unsortMap.put("m", 2);
        unsortMap.put("f", 9);

        System.out.println("Original...");
        System.out.println(unsortMap);

        //sort by values, and reserve it, 10,9,8,7,6...
        Map result = unsortMap.entrySet().stream()
                .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));


        //Alternative way
        Map result2 = new LinkedHashMap<>();
        unsortMap.entrySet().stream()
                .sorted(Map.Entry.comparingByValue().reversed())
                .forEachOrdered(x -> result2.put(x.getKey(), x.getValue()));

        System.out.println("Sorted...");
        System.out.println(result);
        System.out.println(result2);

    }
}

Sortie

Original...
{a=6, b=5, c=20, d=1, e=7, f=9, g=50, y=8, z=10, m=2, n=99}

Sorted...
{n=99, g=50, c=20, z=10, f=9, y=8, e=7, a=6, b=5, m=2, d=1}
{n=99, g=50, c=20, z=10, f=9, y=8, e=7, a=6, b=5, m=2, d=1}

4. Carte

Le Stream ne peut pas trier directement lesMap<Object,Object>. Pour le résoudre, convertissez-le enMap<String,String>, consultez l'exemple ci-dessous.

Note
Si vous avez une meilleure idée de le trier, faites-le moi savoir.

DisplayApp.java

package com.example;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.stream.Collectors;

public class DisplayApp {

    public static void main(String[] args) {

        Properties properties = System.getProperties();
        // not easy to sort this
        Set> entries = properties.entrySet();

        LinkedHashMap collect = entries.stream()
                //Map
                .collect(Collectors.toMap(k -> (String) k.getKey(), e -> (String) e.getValue()))
                .entrySet()
                .stream()
                .sorted(Map.Entry.comparingByKey())
                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));

        collect.forEach((k, v) -> System.out.println(k + ":" + v));

    }

}

Note
Vous n'utilisez pas Java 8? Essayez cette méthode classique poursort a Map in Java.

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Java 8 - Comment trier une carte