Apache Commons - Learn Java by Examples

How do I convert an array to a Map?

By I Wayan Saryada in Apache Commons, Commons Lang Last modified: June 3, 2024 0 Comment

This example uses the Apache Commons Lang’s ArrayUtils.toMap() method to convert a two-dimensional array into a Map object.

To convert a two-dimensional array into a Map object, each element of the two-dimensional array must be an array with at least two elements where the first element will be the key and the second element will be the value.

package org.kodejava.commons.lang;

import java.util.Map;

import org.apache.commons.lang3.ArrayUtils;

public class ArrayToMapExample {

    public static void main(String[] args) {
        // A two-dimensional array of country capital.
        String[][] countries = {{"United States", "Washington, D.C."},
                {"United Kingdom", "London"},
                {"Netherlands", "Amsterdam"},
                {"Japan", "Tokyo"},
                {"France", "Paris"}};

        // Convert an array to a Map.
        Map<Object, Object> capitals = ArrayUtils.toMap(countries);
        for (Object key : capitals.keySet()) {
            System.out.printf("%s is the capital of %s.%n", capitals.get(key), key);
        }
    }
}

The result of our code snippet:

London is the capital of United Kingdom.
Amsterdam is the capital of Netherlands.
Paris is the capital of France.
Washington, D.C. is the capital of United States.
Tokyo is the capital of Japan.

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.14.0</version>
</dependency>

How do I reverse array elements order?

In this example we are going to use the ArraysUtils helper class from the Apache Commons Lang library to reverse the order of array elements. The method to reverse the order of array elements is ArrayUtils.reverse() method.

The ArrayUtils.reverse() method is overloaded, so we can reverse another type of array such as java.lang.Object, long, int, short, char, byte, double, float and boolean.

package org.kodejava.commons.lang;

import org.apache.commons.lang3.ArrayUtils;

public class ArrayReverseExample {

    public static void main(String[] args) {
        // Define the "colors" array.
        String[] colors = {"Red", "Green", "Blue", "Cyan", "Yellow", "Magenta"};
        System.out.println(ArrayUtils.toString(colors));

        // Now we reverse the order of array elements.
        ArrayUtils.reverse(colors);
        System.out.println(ArrayUtils.toString(colors));
    }
}

Here is the output of the code snippet above:

{Red,Green,Blue,Cyan,Yellow,Magenta}
{Magenta,Yellow,Cyan,Blue,Green,Red}

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.14.0</version>
</dependency>

How do I create a copy of a file?

By I Wayan Saryada in Apache Commons, Commons IO Last modified: October 2, 2023 0 Comment

This example shows how we can use the Apache Commons IO library to simplify a file copy process.

package org.kodejava.commons.io;

import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;

public class FileCopyExample {
    public static void main(String[] args) {
        // The source file name to be copied.
        File source = new File("README.md");

        // The target file name to which the source file will be copied.
        File target = new File("README-BACKUP.md");

        // A temporary directory where we are going to copy the source file to.
        // Here we use the temporary directory of the operating system, which 
        // can be obtained using java.io.tmpdir property.
        File targetDir = new File(System.getProperty("java.io.tmpdir"));

        try {
            // Using FileUtils.copyFile() method to copy a file.
            System.out.println("Copying " + source + " file to " + target);
            FileUtils.copyFile(source, target);

            // To copy a file to a specified directory, we can use the
            // FileUtils.copyFileToDirectory() method.
            System.out.println("Copying " + source + " file to " + targetDir);
            FileUtils.copyFileToDirectory(source, targetDir);
        } catch (IOException e) {
            // Errors will be reported here if any error occurs during 
            // copying the file
            e.printStackTrace();
        }
    }
}

Maven Dependencies

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

How do I count word occurrences in a string?

By I Wayan Saryada in Apache Commons, Commons Lang Last modified: June 3, 2024 0 Comment

package org.kodejava.commons.lang;

import org.apache.commons.lang3.StringUtils;

public class WordCountDemo {
    public static void main(String[] args) {
        // We have the source text we'll do the search on.
        String source = "From the download page, you can download the Java " +
            "Tutorials for browsing offline. Or you can just download " +
            "the example.";
        // The word we want to count its occurrences
        String word = "you";

        // Using StringUtils.countMatches() method we can count the occurrence
        // frequency of a word/letter in the giver source of string.
        int wordFound = StringUtils.countMatches(source, word);

        // Print how many we have found the word
        System.out.println(wordFound + " occurrences of the word '" + word +
            "' was found in the text.");
    }
}

Here is the result of the code above.

2 occurrences of the word 'you' was found in the text.

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.14.0</version>
</dependency>

How do I reverse a string, words or sentences?

By I Wayan Saryada in Apache Commons, Commons Lang Last modified: June 3, 2024 0 Comment

package org.kodejava.commons.lang;

import org.apache.commons.lang3.StringUtils;

public class StringReverseDemo {
    public static void main(String[] args) {
        // We have an original string here that we'll need to reverse.
        String words = "The quick brown fox jumps over the lazy dog";

        // Using StringUtils.reverse we can reverse the string letter by letter.
        String reversed = StringUtils.reverse(words);

        // Now we want to reverse per word, we can use
        // StringUtils.reverseDelimited() method to do this.
        String delimitedReverse = StringUtils.reverseDelimited(words, ' ');

        // Print out the result
        System.out.println("Original: " + words);
        System.out.println("Reversed: " + reversed);
        System.out.println("Delimited Reverse: " + delimitedReverse);
    }
}

Here is the result:

Original: The quick brown fox jumps over the lazy dog
Reversed: god yzal eht revo spmuj xof nworb kciuq ehT
Delimited Reverse: dog lazy the over jumps fox brown quick The

Maven Dependencies

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.14.0</version>
</dependency>