Other Libraries - Learn Java by Examples

How do I convert an array of object to an array of primitive?

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

In the code example below we demonstrate the ArrayUtils.toPrimitive() method to convert an array of Integer object to an array of its primitive type. Besides converting an array of Integer objects, this method is overloaded to accept other types of object’s array.

package org.kodejava.commons.lang;

import org.apache.commons.lang3.ArrayUtils;

public class ArrayObjectToPrimitiveDemo {
    public static void main(String[] args) {
        // An array of Integer objects.
        Integer[] integers = {1, 2, 3, 5, 8, 13, 21, 34, 55};
        Boolean[] booleans = {Boolean.TRUE, Boolean.TRUE, Boolean.FALSE, Boolean.FALSE};

        // Convert and array of Integer objects into an array of type int.
        int[] ints = ArrayUtils.toPrimitive(integers);
        System.out.println(ArrayUtils.toString(ints));

        // Convert an array of Boolean objects into an array of type boolean.
        boolean[] bools = ArrayUtils.toPrimitive(booleans);
        System.out.println(ArrayUtils.toString(bools));
    }
}

The output of our code snippet:

{1,2,3,5,8,13,21,34,55}
{true,true,false,false}

Maven Dependencies

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

How do I convert an array to a Map?

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?

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

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>