How do I sort strings data using CollationKey class?

When the strings must be compared multiple times, for example when sorting a list of strings. It’s more efficient to use CollationKey class. Using CollationKey to compare strings is generally faster than using Collator.compare().

You can not create CollationKey directly. Rather, generate them by calling Collator.getCollationKey() method. You can only compare CollationKey generated from the same Collator object.

package org.kodejava.example.text;

import java.text.CollationKey;
import java.text.Collator;
import java.util.Arrays;
import java.util.Collections;

public class CollationKeyExample {
    public static void main(String[] args) {
        String[] countries = {
                "German",
                "United Kingdom",
                "United States",
                "French",
                "Japan",
                "Myanmar",
                "India"
        };

        System.out.println("original:");
        System.out.println(Arrays.toString(countries));

        // Gets Collator object of default locale
        Collator collator = Collator.getInstance();

        // Creates and initializes CollationKey array
        CollationKey[] keys = new CollationKey[countries.length];

        for (int i = 0; i < countries.length; i++) {
            // Generate CollationKey by calling
            // Collator.getCollationKey() method then assign into
            // keys which is an array of CollationKey.
            // The CollationKey for the given String based on the 
            // Collator's collation rules.
            keys[i] = collator.getCollationKey(countries[i]);
        }

        // Sort the keys array
        Collections.sort(Arrays.asList(keys));

        // Print out the sorted array
        System.out.println("sorted result: ");
        StringBuilder sb = new StringBuilder("[");
        for (CollationKey key : keys) {
            sb.append(key.getSourceString()).append(",");
        }
        sb.deleteCharAt(sb.length() - 1).append("]");
        System.out.println(sb.toString());
    }
}

Below is the result of the program:

original:
[German, United Kingdom, United States, French, Japan, Myanmar, India]
sorted result: 
[French,German,India,Japan,Myanmar,United Kingdom,United States]

How do I sort an array of string data using RuleBasedCollator class?

We can use the java.text.Collator class to sort strings in language-specific order. Using the java.text.Collator class makes the string not just sorted by the ASCII code of their characters but it will follow the language natural order of the characters.

If the predefined collation rules do not meet your needs, you can design your own rules and assign them to a RuleBasedCollator object. Customized collation rules are contained in a String object that is passed to the RuleBasedCollator constructor.

package org.kodejava.example.text;

import java.text.ParseException;
import java.text.RuleBasedCollator;
import java.util.Arrays;
import java.util.Collections;

public class RuleBasedCollatorDemo {
    public static void main(String[] args) {
        String rule1 = ("< a < b < c");
        String rule2 = ("< c < b < a");
        String rule3 = ("< c < a < b");

        String words[] = {"apple", "banana", "carrot", "apricot", "blueberry", "cabbage"};

        try {
            RuleBasedCollator rb1 = new RuleBasedCollator(rule1);
            RuleBasedCollator rb2 = new RuleBasedCollator(rule2);
            RuleBasedCollator rb3 = new RuleBasedCollator(rule3);

            System.out.println("original: ");
            System.out.println(Arrays.toString(words));

            // Sort based on rule1
            Collections.sort(Arrays.asList(words), rb1);
            System.out.println("rule: " + rb1.getRules());
            System.out.println(Arrays.toString(words));

            // Sort based on rule2
            Collections.sort(Arrays.asList(words), rb2);
            System.out.println("rule: " + rb2.getRules());
            System.out.println(Arrays.toString(words));

            // Sort based on rule3
            Collections.sort(Arrays.asList(words), rb3);
            System.out.println("rule: " + rb3.getRules());
            System.out.println(Arrays.toString(words));
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

Below is the result of sorting strings using a different RuleBasedCollator

original: 
[apple, banana, carrot, apricot, blueberry, cabbage]
rule: < a < b < c
[apple, apricot, banana, blueberry, cabbage, carrot]
rule: < c < b < a
[cabbage, carrot, banana, blueberry, apple, apricot]
rule: < c < a < b
[cabbage, carrot, apple, apricot, banana, blueberry]

How do I sort strings using Collator class?

In this example we demonstrate how to use the java.text.Collator class to sort strings in language-specific order. Using the java.text.Collator class makes the string not just sorted by the ASCII code of their characters but it will follow the language natural order of the characters.

package org.kodejava.example.text;

import java.util.List;
import java.util.ArrayList;
import java.util.Locale;
import java.util.Collections;
import java.text.Collator;

public class StringShortWithCollator {
    public static void main(String[] args) {
        List<String> fruits = new ArrayList<>();
        fruits.add("Guava");
        fruits.add("Banana");
        fruits.add("Orange");
        fruits.add("Mango");
        fruits.add("Apple");

        // Define a collator for US English.
        Collator collator = Collator.getInstance(Locale.US);

        // Sort the list base on the collator
        Collections.sort(fruits, collator);

        for (String fruit : fruits) {
            System.out.println("Fruit = " + fruit);
        }
    }
}

The result of the code snippet above are:

Fruit = Apple
Fruit = Banana
Fruit = Guava
Fruit = Mango
Fruit = Orange