How do I fill array with non-default value?

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

This code snippet will show you how to create array variable and initialized it with a non-default value. By default, when we create an array of something in Java all entries will have its default value. For primitive types like int, long, float the default value are zero (0 or 0.0). For reference types (anything that holds an object in it) will have null as the default value. For boolean variable it will be false.

If you want to initialize the array to different value you can use the Arrays.fill() method. This method will help you to set the value for every element of the array.

Let see the following code snippet as an example:

package org.kodejava.util;

import java.util.Arrays;

public class ArraysFillExample {
    public static void main(String[] args) {
        // Assign -1 to each element of numbers arrays
        int[] numbers = new int[5];
        Arrays.fill(numbers, -1);
        System.out.println("Numbers: " + Arrays.toString(numbers));

        // Assign 1.0f to each element of prices arrays
        float[] prices = new float[5];
        Arrays.fill(prices, 1.0f);
        System.out.println("Prices : " + Arrays.toString(prices));

        // Assign empty string to each element of words arrays
        String[] words = new String[5];
        Arrays.fill(words, "");
        System.out.println("Words  : " + Arrays.toString(words));

        // Assign 9 to each element of the multi array
        int[][] multi = new int[3][3];
        for (int[] array : multi) {
            Arrays.fill(array, 9);
        }
        System.out.println("Multi  : " + Arrays.deepToString(multi));
    }
}

In the code snippet above we utilize the Arrays.fill() utility method to assign value for each element of the int, float and String array. To change the default value of multidimensional array we can’t directly call the Arrays.fill() method. In the example we use for-loop to set each element of the sub-array using the Arrays.fill() method.

The output of the code snippet above are:

Numbers: [-1, -1, -1, -1, -1]
Prices : [1.0, 1.0, 1.0, 1.0, 1.0]
Words  : [, , , , ]
Multi  : [[9, 9, 9], [9, 9, 9], [9, 9, 9]]

How do I escape / display percent sign in printf statement?

By I Wayan Saryada in Core API, Lang Package

You have a problem displaying the % sign when you want to print a number in percentage format using the printf() method. Because the % sign is use as a prefix of format specifiers, you need to escape it if you want to display the % sign as part of the output string.

To escape the percent sign (%) you need to write it twice, like %%. It will print out a single % sign as part of your printf() method output. Let see an example in the code snippet below:

package org.kodejava.lang;

public class EscapePercentSignExample {
    public static void main(String[] args) {
        String format = "The current bank interest rate is %6.2f%%.%n";
        System.out.printf(format, 10f);
    }
}

In the code snippet above we use the following format %6.2f%%.%n which can be explained as:

  • %6.2f format the number (10f) as six characters in width, right justified, with two places after decimal point. The f conversion character means it accept a float value.
  • %% will escape the % sign and print it as part of the output.
  • %n will print out a new line character.

When you execute the code, it will print:

The current bank interest rate is  10.00%.

How to find the difference between two LocalDateTime objects?

By I Wayan Saryada in Java Date Time API 0 Comment

In the previous post, How do I find the difference between two times?, we get the difference between two LocalTime objects in seconds measurement. In this example we will get the difference between two LocalDateTime objects and get the difference between these objects in years, months, days, hours, minutes, seconds and milliseconds.

package org.kodejava.datetime;

import java.time.LocalDateTime;
import java.time.Month;
import java.time.temporal.ChronoUnit;

public class LocalDateTimeDiff {
    public static void main(String[] args) {
        LocalDateTime from = LocalDateTime.of(2021, Month.JANUARY, 10, 10, 0, 30);
        LocalDateTime to = LocalDateTime.now();

        LocalDateTime fromTemp = LocalDateTime.from(from);
        long years = fromTemp.until(to, ChronoUnit.YEARS);
        fromTemp = fromTemp.plusYears(years);

        long months = fromTemp.until(to, ChronoUnit.MONTHS);
        fromTemp = fromTemp.plusMonths(months);

        long days = fromTemp.until(to, ChronoUnit.DAYS);
        fromTemp = fromTemp.plusDays(days);

        long hours = fromTemp.until(to, ChronoUnit.HOURS);
        fromTemp = fromTemp.plusHours(hours);

        long minutes = fromTemp.until(to, ChronoUnit.MINUTES);
        fromTemp = fromTemp.plusMinutes(minutes);

        long seconds = fromTemp.until(to, ChronoUnit.SECONDS);
        fromTemp = fromTemp.plusSeconds(seconds);

        long millis = fromTemp.until(to, ChronoUnit.MILLIS);

        System.out.println("From = " + from);
        System.out.println("To   = " + to);
        System.out.printf("The difference is %s years, %s months, %s days, " +
                        "%s hours, %s minutes, %s seconds, %s millis",
                years, months, days, hours, minutes, seconds, millis);
    }
}

The result of the code snippet above when executed is:

From = 2021-01-10T10:00:30
To   = 2021-11-17T15:07:37.913247900
The difference is 0 years, 10 months, 7 days, 5 hours, 7 minutes, 7 seconds, 913 millis

How do I find the difference between two times?

By I Wayan Saryada in Java Date Time API 0 Comment

The following code snippet show you how to find the difference between two time objects represented by LocalTime class. To get the difference between two LocalTime objects we can use the Duration.between() method. This method returns a Duration object, to get the difference in seconds we call the getSeconds() method.

Here a code snippet to demonstrate it.

package org.kodejava.datetime;

import java.time.*;

public class TimeDifference {
    public static void main(String[] args) {
        LocalTime start = LocalTime.now();
        LocalTime end = LocalTime.of(16, 59, 55);
        Duration duration = Duration.between(start, end);

        System.out.printf("Seconds between %s and %s is: %s seconds.%n",
                start, end, duration.getSeconds());

        diffLocalDateTime();
        diffInstant();
    }

    /**
     * Difference between two LocalDateTime objects.
     */
    public static void diffLocalDateTime() {
        LocalDateTime dt1 = LocalDateTime.now();
        LocalDateTime dt2 = LocalDateTime.now(ZoneId.of("GMT+0"));
        Duration duration = Duration.between(dt1, dt2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }

    /**
     * Difference between two Instant objects.
     */
    public static void diffInstant() {
        Instant instant1 = Instant.now();
        Instant instant2 = Instant.EPOCH;
        Duration duration = Duration.between(instant1, instant2);
        System.out.printf("Duration = %s seconds.%n", duration.getSeconds());
    }
}

Using the Duration.between() we can also get the difference between two LocalDateTime objects and two Instant object as seen in the diffLocalDateTime() method and diffInstant method in the code snippet above.

The result of the code snippet:

Seconds between 15:05:35.401317900 and 16:59:55 is: 6859 seconds.
Duration = -28800 seconds.
Duration = -1637132736 seconds.

How do I parse negative number in parentheses?

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

In financial application negative numbers are often represented in parentheses. In this post we will learn how we can parse or convert the negative number in parentheses to produce the represented number value. To parse text / string to a number we can use the java.text.DecimalFormat class.

Beside number in parentheses, in this example we also parse negative number that use the minus sign with the currency symbol like $. Let’s jump to the code snippet below:

package org.kodejava.text;

import java.text.DecimalFormat;

public class NegativeNumberParse {
    // Pattern for parsing negative number.
    public static final String PATTERN1 = "#,##0.00;(#,##0.00)";
    public static final String PATTERN2 = "$#,##0.00;-$#,##0.00";

    public static void main(String[] args) throws Exception {
        DecimalFormat df = new DecimalFormat(PATTERN1);

        String number1 = "(1000)";
        String number2 = "(1,500.99)";

        System.out.println("number1 = " + df.parse(number1));
        System.out.println("number2 = " + df.parse(number2));

        df = (DecimalFormat) DecimalFormat.getInstance();
        df.applyPattern(PATTERN2);

        String number3 = "-$1000";
        String number4 = "-$1,500.99";

        System.out.println("number3 = " + df.parse(number3));
        System.out.println("number4 = " + df.parse(number4));
    }
}

And here are the results of our code snippet above:

number1 = -1000
number2 = -1500.99
number3 = -1000
number4 = -1500.99

If you need to display or format negative numbers in parentheses you can take a look at the following example How do I display negative number in parentheses?.