How do I handle exceptions using try-catch block?

By I Wayan Saryada in Basic, Core API 0 Comment

An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program’s instructions. When an abnormal situation occurs within a method, an Exception object is thrown. This object contains information about the error or unusual problems that occur.

Creating an exception object and handing it to the runtime system is called throwing an exception. If you want to deal with the exceptions where they occur, you can include three kinds of code blocks in a method to handle them. try, catch, and finally blocks.

  • The try block encloses code that may give rise to one or more exceptions.
  • The catch block encloses code that is intended to handle exceptions to a particular type that may be thrown in the associated try block.
  • The code in a finally block is always executed before the method ends, regardless of whether any exceptions are thrown in the try block.
package org.kodejava.basic;

public class ExceptionHandlerExample {

    public static void main(String[] args) {
        int x = 1, y = 0, z = 0;

        try {
            // divide by 0 will throw an exception
            z = ExceptionHandlerExample.divide(x, y);
            System.out.println("z = " + z);
        } catch (ArithmeticException e) {
            e.printStackTrace();
        } finally {
            System.out.println("Finally block is always executed.");
        }
    }

    /**
     * Divide the given first number by the second number.
     *
     * @param x the first number.
     * @param y the second number.
     * @return the result of division.
     * @throws RuntimeException when an exception occurs.
     */
    private static int divide(int x, int y) throws RuntimeException {
        return x / y;
    }
}

Here is what happening when we run the program:

java.lang.ArithmeticException: / by zero
    at org.kodejava.basic.ExceptionHandlerExample.divide(ExceptionHandlerExample.java:28)
    at org.kodejava.basic.ExceptionHandlerExample.main(ExceptionHandlerExample.java:10)
Finally block is always executed.

How do I break a paragraph into sentences?

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

This example show you how to use the BreakIterator.getSentenceInstance() to breaks a paragraphs into sentences that composes the paragraph. To get the BreakIterator instance we call the getSentenceInstance() factory method and passes a locale information.

In the count(BreakIterator bi, String source) method we iterate the break to extract sentences that composes the paragraph which value is stored in the paragraph variable.

package org.kodejava.text;

import java.text.BreakIterator;
import java.util.Locale;

public class BreakSentenceExample {
    public static void main(String[] args) {
        String paragraph = """
                Line boundary analysis determines where a text \
                string can be broken when line-wrapping. The \
                mechanism correctly handles punctuation and \
                hyphenated words. Actual line breaking needs to \
                also consider the available line width and is \
                handled by higher-level software.
                """;

        BreakIterator iterator = BreakIterator.getSentenceInstance(Locale.US);

        int sentences = count(iterator, paragraph);
        System.out.println("Number of sentences: " + sentences);
    }

    private static int count(BreakIterator bi, String source) {
        int counter = 0;
        bi.setText(source);

        int lastIndex = bi.first();
        while (lastIndex != BreakIterator.DONE) {
            int firstIndex = lastIndex;
            lastIndex = bi.next();

            if (lastIndex != BreakIterator.DONE) {
                String sentence = source.substring(firstIndex, lastIndex);
                System.out.println("sentence = " + sentence);
                counter++;
            }
        }
        return counter;
    }
}

Our program will print the following result on the console screen:

sentence = Line boundary analysis determines where a text string can be broken when line-wrapping. 
sentence = The mechanism correctly handles punctuation and hyphenated words. 
sentence = Actual line breaking needs to also consider the available line width and is handled by higher-level software.

Number of sentences: 3

How do I break a text or sentence into words?

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

At first, it might look simple. We can just split the text using the String.split(), the word is split using space. But what if a word ends with questions marks (?) or exclamation marks (!) instead? There might be some other rules that we also need to care.

Using the java.text.BreakIterator makes it much simpler. The class’s getWordInstance() factory method creates a BreakIterator instance for words break. Instantiating a BreakIterator and passing a locale information makes the iterator to breaks the text or sentence according the rule of the locale. This is really helpful when we are working with a complex language such as Japanese or Chinese.

Let us see an example of using the BreakIterator below.

package org.kodejava.text;

import java.text.BreakIterator;
import java.util.Locale;

public class BreakIteratorExample {
    public static void main(String[] args) {
        String data = "The quick brown fox jumps over the lazy dog.";
        String search = "dog";

        // Gets an instance of BreakIterator for word break for the
        // given locale. We can instantiate a BreakIterator without
        // specifying the locale. The locale is important when we
        // are working with languages like Japanese or Chinese where
        // the breaks standard may be different compared to English.
        BreakIterator bi = BreakIterator.getWordInstance(Locale.US);

        // Set the text string to be scanned.
        bi.setText(data);

        // Iterates the boundary / breaks
        System.out.println("Iterates each word: ");
        int count = 0;
        int lastIndex = bi.first();
        while (lastIndex != BreakIterator.DONE) {
            int firstIndex = lastIndex;
            lastIndex = bi.next();

            if (lastIndex != BreakIterator.DONE
                    && Character.isLetterOrDigit(data.charAt(firstIndex))) {
                String word = data.substring(firstIndex, lastIndex);
                System.out.printf("'%s' found at (%s, %s)%n",
                        word, firstIndex, lastIndex);

                // Counts how many times the word dog occurs.
                if (word.equalsIgnoreCase(search)) {
                    count++;
                }
            }
        }

        System.out.println("Number of word '" + search + "' found = " + count);
    }
}

Here are the program output:

Iterates each word: 
'The' found at (0, 3)
'quick' found at (4, 9)
'brown' found at (10, 15)
'fox' found at (16, 19)
'jumps' found at (20, 25)
'over' found at (26, 30)
'the' found at (31, 34)
'lazy' found at (35, 39)
'dog' found at (40, 43)
Number of word 'dog' found = 1

How do I sort strings data using CollationKey class?

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

When the strings must be compared multiple times, for example when sorting a list of strings. It’s more efficient to use CollationKey class. Using CollationKey to compare strings is generally faster than using Collator.compare().

You can not create CollationKey directly. Rather, generate them by calling Collator.getCollationKey() method. You can only compare CollationKey generated from the same Collator object.

package org.kodejava.text;

import java.text.CollationKey;
import java.text.Collator;
import java.util.Arrays;

public class CollationKeyExample {
    public static void main(String[] args) {
        String[] countries = {
                "German",
                "United Kingdom",
                "United States",
                "French",
                "Japan",
                "Myanmar",
                "India"
        };

        System.out.println("original:");
        System.out.println(Arrays.toString(countries));

        // Gets Collator object of default locale
        Collator collator = Collator.getInstance();

        // Creates and initializes CollationKey array
        CollationKey[] keys = new CollationKey[countries.length];

        for (int i = 0; i < countries.length; i++) {
            // Generate CollationKey by calling
            // Collator.getCollationKey() method then assign into
            // keys which is an array of CollationKey.
            // The CollationKey for the given String based on the 
            // Collator's collation rules.
            keys[i] = collator.getCollationKey(countries[i]);
        }

        // Sort the keys array
        Arrays.sort(keys);

        // Print out the sorted array
        System.out.println("sorted result: ");
        StringBuilder sb = new StringBuilder();
        for (CollationKey key : keys) {
            sb.append(key.getSourceString()).append(",");
        }
        System.out.println(sb);
    }
}

Below is the result of the program:

original:
[German, United Kingdom, United States, French, Japan, Myanmar, India]
sorted result: 
French,German,India,Japan,Myanmar,United Kingdom,United States,

How do I sort an array of string data using RuleBasedCollator class?

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

We can 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.

If the predefined collation rules do not meet your needs, you can design your own rules and assign them to a RuleBasedCollator object. Customized collation rules are contained in a String object that is passed to the RuleBasedCollator constructor.

package org.kodejava.text;

import java.text.ParseException;
import java.text.RuleBasedCollator;
import java.util.Arrays;

public class RuleBasedCollatorDemo {
    public static void main(String[] args) {
        String rule1 = ("< a < b < c");
        String rule2 = ("< c < b < a");
        String rule3 = ("< c < a < b");

        String[] words = {
                "apple",
                "banana",
                "carrot",
                "apricot",
                "blueberry",
                "cabbage"
        };

        try {
            RuleBasedCollator rb1 = new RuleBasedCollator(rule1);
            RuleBasedCollator rb2 = new RuleBasedCollator(rule2);
            RuleBasedCollator rb3 = new RuleBasedCollator(rule3);

            System.out.println("original: ");
            System.out.println(Arrays.toString(words));

            // Sort based on rule1
            Arrays.sort(words, rb1);
            System.out.println("rule: " + rb1.getRules());
            System.out.println(Arrays.toString(words));

            // Sort based on rule2
            Arrays.sort(words, rb2);
            System.out.println("rule: " + rb2.getRules());
            System.out.println(Arrays.toString(words));

            // Sort based on rule3
            Arrays.sort(words, rb3);
            System.out.println("rule: " + rb3.getRules());
            System.out.println(Arrays.toString(words));
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }
}

Below is the result of sorting strings using a different RuleBasedCollator

original: 
[apple, banana, carrot, apricot, blueberry, cabbage]
rule: < a < b < c
[apple, apricot, banana, blueberry, cabbage, carrot]
rule: < c < b < a
[cabbage, carrot, banana, blueberry, apple, apricot]
rule: < c < a < b
[cabbage, carrot, apple, apricot, banana, blueberry]