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