How do I search collection elements?

By Wayan in Core API, Util Package 0 Comment

This code example use the Collections.binarySearch() to search an specified object inside a specified collections. Prior to calling the binarySearch() method we need to sort the elements of the collection. If the object is not sorted according to their natural order the search result will be undefined.

package org.kodejava.util;

import java.util.Arrays;
import java.util.LinkedList;
import java.util.Collections;
import java.text.DateFormatSymbols;

public class CollectionSearch {
    public static void main(String[] args) {
        DateFormatSymbols dfs = new DateFormatSymbols();

        LinkedList<String> monthList =
                new LinkedList<>(Arrays.asList(dfs.getMonths()));

        // Sort the collection elements
        Collections.sort(monthList);
        System.out.println("Months = " + monthList);

        // Get the position of November inside the monthList. It returns a positive
        // value if the item found in the monthList.
        int index = Collections.binarySearch(monthList, "November");
        if (index > 0) {
            System.out.println("Found at index = " + index);
            System.out.println("Month = " + monthList.get(index));
        }
    }
}

The output of the code snippet above is below.

Months = [, April, August, December, February, January, July, June, March, May, November, October, September]
Found at index = 10
Month = November

How do I sort files based on their last modified date?

By Wayan in Apache Commons, Commons IO 0 Comment

This example demonstrates how to use Apache Commons IO LastModifiedFileComparator class to sort files based on their last modified date in ascending and descending order. There are two comparators defined in this class, the LASTMODIFIED_COMPARATOR and the LASTMODIFIED_REVERSE.

package org.kodejava.commons.io;

import static org.apache.commons.io.comparator.LastModifiedFileComparator.*;

import java.io.File;
import java.util.Arrays;

public class FileSortLastModified {
    public static void main(String[] args) {
        File dir = new File(System.getProperty("user.home"));
        File[] files = dir.listFiles();

        if (files != null) {
            // Sort files in ascending order based on file's last
            // modification date.
            System.out.println("Ascending order.");
            Arrays.sort(files, LASTMODIFIED_COMPARATOR);
            FileSortLastModified.displayFileOrder(files);

            System.out.println("------------------------------------");

            // Sort files in descending order based on file's last
            // modification date.
            System.out.println("Descending order.");
            Arrays.sort(files, LASTMODIFIED_REVERSE);
            FileSortLastModified.displayFileOrder(files);
        }
    }

    private static void displayFileOrder(File[] files) {
        for (File file : files) {
            System.out.printf("%2$td/%2$tm/%2$tY - %s%n", file.getName(),
                    file.lastModified());
        }
    }
}

Here are the example results produced by the code snippet:

Ascending order.
15/12/2020 - ntuser.dat.LOG1
15/12/2020 - ntuser.ini
15/12/2020 - .m2
18/12/2020 - Contacts
22/12/2020 - Videos
01/01/2021 - VirtualBox VMs
02/01/2021 - Desktop
02/01/2021 - Documents
------------------------------------------
Descending order.
02/01/2021 - Documents
02/01/2021 - Desktop
01/01/2021 - VirtualBox VMs
22/12/20202 - Videos
18/12/20202 - Contacts
15/12/20202 - .m2
15/12/20202 - ntuser.ini
15/12/20202 - ntuser.dat.LOG1

Maven Dependencies

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.14.0</version>
</dependency>

Maven Central

How do I sort strings using Collator class?

By Wayan in Core API, Text Package 0 Comment

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.text;

import java.util.List;
import java.util.ArrayList;
import java.util.Locale;
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
        fruits.sort(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

How do I sort items in a Set?

By Wayan in Core API, Util Package 0 Comment

The trick to sort a java.util.Set is to use the implementation of a java.util.SortedSet such as the java.util.TreeSet class. The example below shows you the result of using the java.util.TreeSet class, in which the items in it will be sorted based on the element’s natural order.

package org.kodejava.util;

import java.util.Set;
import java.util.TreeSet;

public class TreeSetDemo {
    public static void main(String[] args) {
        // The TreeSet class is an implementation of a SortedSet, this means
        // that when you are using the TreeSet to store you data collections
        // you'll get the items ordered base on its elements natural order.
        Set<String> set = new TreeSet<>();

        // In the example below we add some letters to the TreeSet, this mean
        // that the alphabets will be ordered based on the alphabet order
        // which is from A to Z.
        set.add("Z");
        set.add("A");
        set.add("F");
        set.add("B");
        set.add("H");
        set.add("X");
        set.add("N");

        for (String item : set) {
            System.out.print(item + " ");
        }
    }
}

This demo prints:

A B F H N X Z

How do I sort items of an ArrayList?

By Wayan in Core API, Util Package 0 Comment

This example shows you how we can sort items of an ArrayList using the Collections.sort() method. Beside accepting the list object to be sorted we can also pass a Comparator implementation to define the sorting behaviour such as sorting in descending or ascending order.

package org.kodejava.util;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class ArrayListSortExample {
    public static void main(String[] args) {
        /*
         * Create a collections of colours
         */
        List<String> colours = new ArrayList<>();
        colours.add("red");
        colours.add("green");
        colours.add("blue");
        colours.add("yellow");
        colours.add("cyan");
        colours.add("white");
        colours.add("black");

        /*
         * We can sort items of a list using the Collections.sort() method.
         * We can also reverse the order of the sorting by passing the
         * Collections.reverseOrder() comparator.
         */
        Collections.sort(colours);
        System.out.println(Arrays.toString(colours.toArray()));

        colours.sort(Collections.reverseOrder());
        System.out.println(Arrays.toString(colours.toArray()));
    }
}

The code will output:

[black, blue, cyan, green, red, white, yellow]
[yellow, white, red, green, cyan, blue, black]