How do I write character class subtraction regex?

By Wayan in Regex 0 Comment

You can use subtraction to negate one or more nested character classes. This example creates a single character class that matches everything from a to z, except the vowels (‘a’, ‘i’, ‘u’, ‘e’, ‘o’). This can be written in a subtraction pattern as [a-z&&[^aiueo]].

package org.kodejava.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class CharacterClassSubtractionDemo {
    public static void main(String[] args) {
        // Define regex that will search characters from 'a' to 'z'
        // and excluding vowels.
        String regex = "[a-z&&[^aiueo]]";

        // Compiles the given regular expression into a pattern and
        // Creates a matcher that will match the given input against
        // this pattern.
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher("The quick brown fox.");

        // Find every match and print it
        while (matcher.find()) {
            System.out.format("Text \"%s\" found at %d to %d.%n",
                    matcher.group(), matcher.start(), matcher.end());
        }
    }
}

Here are the result of the program:

Text "h" found at 1 to 2.
Text "q" found at 4 to 5.
Text "c" found at 7 to 8.
Text "k" found at 8 to 9.
Text "b" found at 10 to 11.
Text "r" found at 11 to 12.
Text "w" found at 13 to 14.
Text "n" found at 14 to 15.
Text "f" found at 16 to 17.
Text "x" found at 18 to 19.

How do I write simple character class regex?

By Wayan in Regex 0 Comment

A character class in the context of regular expression is a set of characters enclosed within a square brackets "[]". It specifies the characters that will successfully match a single character from the given input.

A simple class, the most basic form of character class, is formed simply by placing a set of characters side-by-side within square brackets. For example the regular expression b[ai]t will match the words "bit" or "bat" because the pattern defines a character class accepting either "i" or "a" as the middle character.

package org.kodejava.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class CharacterClassesSimpleClassDemo {
    public static void main(String[] args) {
        // Creating a simple class type of character classes.
        // The regular expression below will search all sequences
        // of string that begins with 'b', ends with 't' and have
        // a middle letter of 'a' or 'i'.
        String regex = "b[ai]t";

        // Compiles the pattern and obtains the matcher object.
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher =
                pattern.matcher("I'm a little bit afraid of bats " +
                        "but not cats.");

        // Find every match and prints it.
        while (matcher.find()) {
            System.out.format("Text \"%s\" found at %d to %d.%n",
                    matcher.group(), matcher.start(), matcher.end());
        }
    }
}

The program will print the following output:

Text "bit" found at 13 to 16.
Text "bat" found at 27 to 30.

How do I write negated character class regex?

By Wayan in Regex 0 Comment

A negation class is a character class that begins with a ^ metacharacter which will exclude a set of defined characters within a square brackets. For example the negation class h[^ao]t in the example below match only the word hit and exclude the words hat and hot.

package org.kodejava.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class CharacterClassesNegationClassDemo {
    public static void main(String[] args) {
        // Defines a regular expression that will search all
        // sequences of string that begin with 'h' and end with 't'
        // and have a middle letter except those appearing to the
        // right of the ^ character within the square brackets
        // ('a' and 'o')
        String regex = "h[^ao]t";

        // Compiles the pattern and obtains the matcher object.
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher =
                pattern.matcher("Wow, that hot hat will make a hit");

        // Find every match and prints it.
        while (matcher.find()) {
            System.out.format("Text \"%s\" found at %d to %d.%n",
                    matcher.group(), matcher.start(), matcher.end());
        }
    }
}

The program output the following result:

Text "hit" found at 30 to 33.

How do I write range character class regex?

By Wayan in Regex 0 Comment

To define a character class that includes a range of values, put - metacharacter between the first and last character to be matched. For example [a-e]. You can also specify multiple ranges like this [a-zA-Z]. This will match any letter of the alphabet from a to z (lowercase) or A to Z (uppercase).

In the example below we are matching the word that begins with bat and ends with a single number that have a value range from 3 to 7.

package org.kodejava.regex;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class CharacterClassesRangeClassDemo {
    public static void main(String[] args) {
        // Defines regex that will search all sequences of string
        // that begin with bat and number which range [3-7]
        String regex = "bat[3-7]";
        String input =
                "bat1, bat2, bat3, bat4, bat5, bat6, bat7, bat8";

        // Compiles the given regular expression into a pattern.
        Pattern pattern = Pattern.compile(regex);

        // Creates a matcher that will match the given input
        // against this pattern.
        Matcher matcher = pattern.matcher(input);

        // Find every match and prints it.
        while (matcher.find()) {
            System.out.format("Text \"%s\" found at %d to %d.%n",
                    matcher.group(), matcher.start(),
                    matcher.end());
        }
    }
}

The program will match the following string from the input:`

Text "bat3" found at 12 to 16.
Text "bat4" found at 18 to 22.
Text "bat5" found at 24 to 28.
Text "bat6" found at 30 to 34.
Text "bat7" found at 36 to 40.

How do I set and get the contents of JTextArea?

By Wayan in Swing 0 Comment

To set and get the contents of a JTextArea you can use the setText(String text) and getText() methods. In the code below we create a JTextArea and sets its contents after we create a new instance of JTextArea. To get the contents we use the action on a button. When the button is pressed the contents of the JTextArea is read using the getText() method. This method return a String object.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class TextAreaGetContent extends JPanel {
    public TextAreaGetContent() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new TextAreaGetContent();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTextArea Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(TextAreaGetContent::showFrame);
    }

    private void initializeUI() {
        this.setLayout(new BorderLayout());
        this.setPreferredSize(new Dimension(500, 200));

        final JTextArea textArea = new JTextArea();

        // Set the contents of the JTextArea.
        String text = "The quick brown fox jumps over the lazy dog.";
        textArea.setText(text);
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);

        JScrollPane pane = new JScrollPane(textArea);
        pane.setPreferredSize(new Dimension(500, 200));
        pane.setVerticalScrollBarPolicy(
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        JButton button = new JButton("Get Contents");
        button.addActionListener(e -> {
            // Get the contents of the JTextArea component.
            String contents = textArea.getText();
            System.out.println("contents = " + contents);
        });

        this.add(pane, BorderLayout.CENTER);
        this.add(button, BorderLayout.SOUTH);
    }
}

The output of the code snippet above is:

Set and Get the Content of JTextArea

How do I set the tab size in JTextArea?

By Wayan in Swing 0 Comment

In this example you will be shown how to set or change the tab size for the JTextArea component. You can use the setTabSize(int size) to define the tab size. For this demo we create a combo box that have some integer values which will be used to define the tab size. When you change the selected item in the combo box the JTextArea tab size will be change immediately.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class TextAreaSetTabSize extends JPanel {
    public TextAreaSetTabSize() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new TextAreaSetTabSize();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTextArea Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(TextAreaSetTabSize::showFrame);
    }

    private void initializeUI() {
        this.setLayout(new BorderLayout());
        this.setPreferredSize(new Dimension(500, 200));

        JLabel label = new JLabel("Tab size: ");
        Object[] items = {2, 4, 8, 10, 20};
        final JComboBox<Object> comboBox = new JComboBox<>(items);

        JPanel tabPanel = new JPanel(new FlowLayout());
        tabPanel.add(label);
        tabPanel.add(comboBox);

        this.add(tabPanel, BorderLayout.NORTH);

        final JTextArea textArea = new JTextArea();
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);

        // Sets the number of characters to expand tabs to.
        textArea.setTabSize((Integer) comboBox.getSelectedItem());
        comboBox.addItemListener(e -> textArea.setTabSize(
                (Integer) comboBox.getSelectedItem()));

        JScrollPane pane = new JScrollPane(textArea);
        pane.setPreferredSize(new Dimension(500, 200));
        pane.setVerticalScrollBarPolicy(
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        this.add(pane, BorderLayout.CENTER);
    }
}

The output of the code snippet above is:

JTextArea Tab Size Demo

How do I use the || operator in Java?

By Wayan in Basic, Core API 0 Comment

The || operator or conditional OR operator operates on two boolean expressions. This operator exhibit “short-circuiting” behavior, which means that the second operand is evaluated only if needed.

The || operator evaluate only boolean values. For an OR (||) expression it will return true if either of the operand is true. If the first operand resolves true, then the second operand will not evaluate, because the complete expression will return true.

package org.kodejava.basic;

public class ConditionalORDemo {
    public static void main(String[] args) {
        // the second operand (5<3) is not evaluated, because the
        // first operand return true, the result of complete
        // expression will be true
        boolean a = (1 == 1) || (5 < 3);

        // the first operand return false, the second operand is
        // evaluated to check the result of the second expression.
        // If the second operand resolves to true, the complete
        // expression return true, otherwise return false.
        boolean b = (5 < 3) || (2 == 3);
        boolean c = (5 < 3) || (1 == 1);

        System.out.println("result a: " + a);
        System.out.println("result b: " + b);
        System.out.println("result c: " + c);
    }
}

The program prints the following output:

result a: true
result b: false
result c: true

How do I use the boolean negation (!) operator in Java?

By Wayan in Basic, Core API 0 Comment

The ! operator is a logical compliment operator. The operator inverts the value of a boolean expression.

package org.kodejava.basic;

public class NegationOperator {
    public static void main(String[] args) {
        // negate the result of boolean expressions
        boolean negate = !(2 < 3);
        boolean value = !false;

        System.out.println("result: " + negate);
        System.out.println("value : " + value);
    }
}

Here is the result of the program:

result: false
value : true

How do I wrap the text lines in JTextArea?

By Wayan in Swing 0 Comment

To wrap the lines of JTextArea we need to call the setLineWrap(boolean wrap) method and pass a true boolean value as the parameter. The setWrapStyleWord(boolean word) method wrap the lines at word boundaries when we set it to true.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class TextAreaWrapDemo extends JPanel {
    public TextAreaWrapDemo() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new TextAreaWrapDemo();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTextArea Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(TextAreaWrapDemo::showFrame);
    }

    private void initializeUI() {
        this.setLayout(new BorderLayout());
        this.setPreferredSize(new Dimension(500, 200));

        JTextArea textArea = new JTextArea(5, 40);

        String text = """
                The quick brown fox jumps over the lazy dog. \
                The quick brown fox jumps over the lazy dog. \
                The quick brown fox jumps over the lazy dog.
                """;

        textArea.setText(text);
        textArea.setFont(new Font("Arial", Font.BOLD, 18));

        // Wrap the lines of the JTextArea if it does not fit in the
        // current allocated with of the JTextArea.
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);
        JScrollPane scrollPane = new JScrollPane(textArea);

        this.add(scrollPane, BorderLayout.CENTER);
    }
}

The output of the code snippet above is:

JTextArea Wrap Text Line Demo

How do I match a regex pattern in case-insensitive?

By Wayan in Regex 0 Comment

Finding the next subsequence of the input sequence that matches the pattern while ignoring the case of the string in regular expression can simply apply by create a pattern using compile(String regex, int flags) method and specifies a second argument with PATTERN.CASE_INSENSITIVE constant.

package org.kodejava.regex;

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class RegexIgnoreCaseDemo {
    public static void main(String[] args) {
        String sentence =
                "The quick brown fox and BROWN tiger jumps over the lazy dog";

        Pattern pattern = Pattern.compile("brown", Pattern.CASE_INSENSITIVE);
        Matcher matcher = pattern.matcher(sentence);

        while (matcher.find()) {
            System.out.format("Text \"%s\" found at %d to %d.%n",
                    matcher.group(), matcher.start(), matcher.end());
        }
    }
}

Here is the result of the program:

Text "brown" found at 10 to 15.
Text "BROWN" found at 24 to 29.