How do I clear the content of an array?

By I Wayan Saryada in Core API, Util Package 0 Comment

In this example you’ll learn how to clear or reset the content of an array. We can use the java.util.Arrays.fill() method to replace to content of each element in the array. In the example below we create two arrays, names and numbers array. We initialize these arrays with some values and then clear the value by assigning null to each element of the array using the Arrays.fill() method.

package org.kodejava.util;

import java.util.Arrays;

public class ArrayClear {
    public static void main(String[] args) {
        String[] names = {"Alice", "Bob", "Carol"};
        System.out.println("Names = " + Arrays.toString(names));

        // Replace the contents of the names array to null for each array
        // element.
        Arrays.fill(names, null);
        System.out.println("Names = " + Arrays.toString(names));

        Integer[] numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        System.out.println("Numbers = " + Arrays.toString(numbers));

        // Replace the contents of the numbers array to null for each
        // array element.
        Arrays.fill(numbers, null);
        System.out.println("Numbers = " + Arrays.toString(numbers));
    }
}

The output of the code snippet:

Names = [Alice, Bob, Carol]
Names = [null, null, null]
Numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Numbers = [null, null, null, null, null, null, null, null, null, null]

How do I validate input when using Scanner?

By I Wayan Saryada in Core API, Util Package 13 Comments

This example show you how to validate input when using java.util.Scanner. To validate input the Scanner class provides some hasNextXXX() method that can be use to validate input. For example if we want to check whether the input is a valid integer we can use the hasNextInt() method.

In the code snippet below will demonstrate how to validate whether the user provide a positive integer number. The program will repeat until the correct input is supplied.

package org.kodejava.util;

import java.util.Scanner;

public class ScannerValidateInput {
    public static void main(String[] args) {
        ScannerValidateInput demo = new ScannerValidateInput();
        demo.validatePositiveNumber();
    }

    private void validatePositiveNumber() {
        Scanner scanner = new Scanner(System.in);

        int number;
        do {
            System.out.print("Please enter a positive number: ");
            while (!scanner.hasNextInt()) {
                String input = scanner.next();
                System.out.printf("\"%s\" is not a valid number.%n", input);
            }
            number = scanner.nextInt();
        } while (number < 0);

        System.out.printf("You have entered a positive number %d.%n", number);
    }
}

The output produce by the snippet:

Please enter a positive number: qwerty
"qwerty" is not a valid number.
@@@
"@@@" is not a valid number.
-100
Please enter a positive number: 99
You have entered a positive number 99.

Another example is to validate if user correctly input letters to guest a secret word. In the code snippet below if the user does not enter a letter the code will keep asking for a valid letter. It loops until the length of the inputted letters equals to the length of secret word.

package org.kodejava.util;

import java.util.Scanner;

public class ScannerValidateLetter {
    public static void main(String[] args) {
        ScannerValidateLetter demo = new ScannerValidateLetter();
        demo.validateLetter();
    }

    private void validateLetter() {
        String secretWord = "Hello";
        Scanner scanner = new Scanner(System.in);

        int length = 0;
        StringBuilder guess = new StringBuilder();
        do {
            System.out.print("Enter a letter to guess: ");
            char letter = scanner.next().charAt(0);
            if (Character.isLetter(letter)) {
                guess.append(letter);
                length++;
            }
        } while (length < secretWord.length());

        if (secretWord.equalsIgnoreCase(guess.toString())) {
            System.out.println("You are correct!");
        } else {
            System.out.println("Please try again!");
        }
    }
}

Enter a letter to guess: 1
Enter a letter to guess: 2
Enter a letter to guess: H
Enter a letter to guess: e
Enter a letter to guess: l
Enter a letter to guess: l
Enter a letter to guess: o
You are correct!

How do I reverse the order of array elements?

By I Wayan Saryada in Core API, Util Package 0 Comment

In this code snippet you’ll learn how to reverse the order of array elements. To reverse to element order will be using the Collections.reverse() method. This method requires an argument with List type. Because of this we need to convert the array to a List type first. We can use the Arrays.asList() to do the conversion. And then we reverse it. To convert the List back to array we can use the Collection.toArray() method.

Let’s see the code snippet below:

package org.kodejava.util;

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

public class ArrayReverse {
    public static void main(String[] args) {
        // Creates an array of Integers and print it out.
        Integer[] numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8};
        System.out.println("Arrays.toString(numbers) = " +
                Arrays.toString(numbers));

        // Convert the int arrays into a List.
        List<Integer> numberList = Arrays.asList(numbers);

        // Reverse the order of the List.
        Collections.reverse(numberList);

        // Convert the List back to array of Integers
        // and print it out.
        numberList.toArray(numbers);
        System.out.println("Arrays.toString(numbers) = " +
                Arrays.toString(numbers));
    }
}

The output of the code snippet above is:

Arrays.toString(numbers) = [0, 1, 2, 3, 4, 5, 6, 7, 8]
Arrays.toString(numbers) = [8, 7, 6, 5, 4, 3, 2, 1, 0]

How do I get all available currency codes?

By I Wayan Saryada in Core API, Util Package 2 Comments

The example presented in this code snippet show you how to get the available currency codes. We will need the locale information and use the Currency class for this example.

package org.kodejava.util;

import java.util.Currency;
import java.util.Locale;
import java.util.Map;
import java.util.TreeMap;

public class CurrencySymbolDemo {
    public static void main(String[] args) {
        CurrencySymbolDemo cs = new CurrencySymbolDemo();

        Map<String, String> currencies = cs.getAvailableCurrencies();
        for (String country : currencies.keySet()) {
            String currencyCode = currencies.get(country);
            System.out.println(country + " => " + currencyCode);
        }
    }

    /**
     * Get the currencies code from the available locales information.
     *
     * @return a map of currencies code.
     */
    private Map<String, String> getAvailableCurrencies() {
        Locale[] locales = Locale.getAvailableLocales();

        // We use TreeMap so that the order of the data in the map sorted
        // based on the country name.
        Map<String, String> currencies = new TreeMap<>();
        for (Locale locale : locales) {
            try {
                currencies.put(locale.getDisplayCountry(),
                        Currency.getInstance(locale).getCurrencyCode());
            } catch (Exception e) {
                // when the locale is not supported
            }
        }
        return currencies;
    }
}

You will have something like this printed on the screen:

...
Honduras => HNL
Hong Kong SAR China => HKD
Hungary => HUF
Iceland => ISK
India => INR
Indonesia => IDR
Iran => IRR
Iraq => IQD
Ireland => EUR
Isle of Man => GBP
...

How do I create a Locale object using a variant?

By I Wayan Saryada in Core API, Util Package 0 Comment

Font differences may force you to use different characters on different platforms. You could then define the Locale objects with the variant codes to identify those differences. The variant codes conform to no standard. They are arbitrary and specific to your application. If you create Locale objects with variant codes only your application will know how to deal with them.

In this example instead of demonstrating to use a different font for different platform we simplify it to just print a different message. We create three different resource bundles for each platform, the Birthday_fr_FR_UNIX.properties, Birthday_fr_FR_MAC.properties and Birthday_fr_FR_WIN.properties. These files will contains different message for each platform.

package org.kodejava.util;

import java.util.Locale;
import java.util.ResourceBundle;

public class LocalePlatform {
    public static void main(String[] args) {
        ResourceBundle res;
        String language = "fr";
        String country = "FR";

        // Construct a locale from language, country, variant. Where the variant
        // can be a variant vendor and browser specific code.
        Locale unix = new Locale(language, country, "UNIX");
        res = ResourceBundle.getBundle("Birthday", unix);
        System.out.println("UNIX: " + res.getString("birthday"));

        Locale mac = new Locale(language, country, "MAC");
        res = ResourceBundle.getBundle("Birthday", mac);
        System.out.println("MAC : " + res.getString("birthday"));

        Locale windows = new Locale(language, country, "WIN");
        res = ResourceBundle.getBundle("Birthday", windows);
        System.out.println("WIN : " + res.getString("birthday"));
    }
}

Here are the contents of the resource bundle files:

Birthday_fr_FR_UNIX.properties

birthday=Unix, Joyeux anniversaire à vous!

Birthday_fr_FR_MAC.properties

birthday=Mac, Joyeux anniversaire à vous!

Birthday_fr_FR_WIN.properties

birthday=Windows, Joyeux anniversaire à vous!