How do I create JComboBox?

By I Wayan Saryada in Swing 0 Comment

A JComboBox allows user to select a value from a drop-down items available in the component. When the combo box set to editable user can enter their own value by typing it directly in the combo box editor. The code below demonstrate how you can create a simple combo box component.

package org.kodejava.swing;

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

public class ComboBoxCreate extends JFrame {
    public ComboBoxCreate() {
        initialize();
    }

    private void initialize() {
        setSize(500, 500);
        setTitle("JComboBox Demo");
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT));

        JLabel label1 = new JLabel("Month  :");
        JLabel label2 = new JLabel("Number :");

        // Create some items for our JComboBox component. In this example we are
        // going to pass an array of string which are the name of the month.
        String[] months = {"January", "February", "March", "April", "Mei", "June",
                "July", "August", "September", "October", "November", "December"};

        // Create a month selection combo box.
        JComboBox<String> comboBox = new JComboBox<>(months);

        // Below, instead of passing directly a string array we create a ComboBoxModel
        // as the combo box data model. Using a model we can for example define the
        // selected item of the combo box.
        ComboBoxModel<String> model =
                new DefaultComboBoxModel<>(new String[]{"1", "2", "3", "4", "5"});
        model.setSelectedItem("3");
        JComboBox<String> numberComboBox = new JComboBox<>(model);

        // We also set the combo box to be editable so that user can enter their own
        // value other that those defined in the combo box.
        numberComboBox.setEditable(true);

        // Add the entire component to out frame content pane.
        getContentPane().add(label1);
        getContentPane().add(comboBox);

        getContentPane().add(label2);
        getContentPane().add(numberComboBox);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new ComboBoxCreate().setVisible(true));
    }
}

How do I format cell style in Excel document?

By I Wayan Saryada in Apache POI 7 Comments

This example demonstrate how to use HSSFCellStyle and HSSFFont to format the cell style in Excel document. Using this class we can define cell border, foreground and background color. We can also define the font we used to display the cell value.

package org.kodejava.poi;

import org.apache.poi.hssf.usermodel.*;
import org.apache.poi.hssf.util.HSSFColor;
import org.apache.poi.ss.usermodel.BorderStyle;
import org.apache.poi.ss.usermodel.FillPatternType;

import java.io.FileOutputStream;
import java.io.IOException;

public class ExcelCellFormat {
    public static void main(String[] args) {
        // Create an instance of workbook and sheet
        try (HSSFWorkbook workbook = new HSSFWorkbook()) {
            HSSFSheet sheet = workbook.createSheet();

            // Create an instance of HSSFCellStyle which will be used to format the
            // cell. Here we define the cell top and bottom border, and we also
            // define the background color.
            HSSFCellStyle style = workbook.createCellStyle();
            style.setBorderTop(BorderStyle.DOUBLE);
            style.setBorderBottom(BorderStyle.THIN);
            style.setFillForegroundColor(
                    HSSFColor.HSSFColorPredefined.GREY_25_PERCENT.getIndex());
            style.setFillPattern(FillPatternType.SOLID_FOREGROUND);

            // We also define the font that we are going to use for displaying the
            // data of the cell. We set the font to ARIAL with 20pt in size and
            // make it BOLD and give blue as the color.
            HSSFFont font = workbook.createFont();
            font.setFontName(HSSFFont.FONT_ARIAL);
            font.setFontHeightInPoints((short) 20);
            font.setBold(true);
            font.setColor(HSSFColor.HSSFColorPredefined.BLUE.getIndex());
            style.setFont(font);

            // We create a simple cell, set its value and apply the cell style.
            HSSFRow row = sheet.createRow(1);
            HSSFCell cell = row.createCell(1);
            cell.setCellValue(new HSSFRichTextString("Hi there... It's me again!"));
            cell.setCellStyle(style);
            sheet.autoSizeColumn((short) 1);

            // Finally, we write out the workbook into an Excel file.
            try (FileOutputStream fos = new FileOutputStream("ExcelDemo.xls")) {
                workbook.write(fos);
            } catch (IOException e) {
                e.printStackTrace();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi</artifactId>
    <version>5.2.5</version>
</dependency>

Maven Central

How do I create an Excel document using Apache POI?

By I Wayan Saryada in Apache POI 2 Comments

This example demonstrate how to create an Excel document using Apache POI library. In this example we create a simple document containing two sheets which have a value on their first cell.

package org.kodejava.poi;

import org.apache.poi.hssf.usermodel.*;

import java.io.FileOutputStream;
import java.io.IOException;

public class CreateExcelDemo {
    public static void main(String[] args) {
        // Creating an instance of HSSFWorkbook.
        try (HSSFWorkbook workbook = new HSSFWorkbook()) {

            // Create two sheets in the Excel document and name it First Sheet and
            // Second Sheet.
            HSSFSheet firstSheet = workbook.createSheet("FIRST SHEET");
            HSSFSheet secondSheet = workbook.createSheet("SECOND SHEET");

            // Manipulate the first sheet by creating an HSSFRow which represent a
            // single row in Excel sheet, the first row started from 0 index. After
            // the row is created we create a HSSFCell in this first cell of the row
            // and set the cell value with an instance of HSSFRichTextString
            // containing the words FIRST SHEET.
            HSSFRow rowA = firstSheet.createRow(0);
            HSSFCell cellA = rowA.createCell(0);
            cellA.setCellValue(new HSSFRichTextString("FIRST SHEET"));

            HSSFRow rowB = secondSheet.createRow(0);
            HSSFCell cellB = rowB.createCell(0);
            cellB.setCellValue(new HSSFRichTextString("SECOND SHEET"));

            // To write out the workbook into a file we need to create an output
            // stream where the workbook content will be written to.
            try (FileOutputStream fos = new FileOutputStream("CreateExcelDemo.xls")) {
                workbook.write(fos);
            } catch (IOException e) {
                e.printStackTrace();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi</artifactId>
    <version>5.2.5</version>
</dependency>

Maven Central

How do I create a PDF document using iText PDF?

By I Wayan Saryada in iText PDF 0 Comment

This example is the first example of the iText PDF series, we are going to start by learning to use the iText PDF library to create a PDF document. We will see how to use the Document class, getting an instance of PdfWriter, creating a simple Paragraph and set the text alignment and the font.

The basic steps to produce a PDF documents are:

  • Create a Document object that represents a PDF document.
  • The PdfWrite object that need the Document and an OutputStream object write the content of the PDF we added to the Document into a PDF file.
  • We add a paragraph into the Document instance using the Paragraph object.
  • Finally, we need to close the document by calling the Document.close() method.

And here is a code example that demonstrate the creation of a PDF document.

package org.kodejava.itextpdf;

import com.itextpdf.text.*;
import com.itextpdf.text.pdf.PdfWriter;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;

public class DocumentCreate {
    public static void main(String[] args) {
        // Create a new document.
        Document document = new Document();
        try {
            // Get an instance of PdfWriter and create a HelloWorld.pdf
            // file as an output.
            PdfWriter.getInstance(document,
                    new FileOutputStream("HelloWorld.pdf"));
            document.open();

            // Create our first paragraph for the pdf document to be
            // created. We also set the alignment and the font of the
            // paragraph.
            String text = "Kode Java website provides beginners to Java " +
                    "programming some examples to use the Java API " +
                    "(Application Programming Interface) to develop " +
                    "applications. Learning from some examples will " +
                    "hopefully decrease the time required to learn " +
                    "Java.";
            Paragraph paragraph = new Paragraph(text);
            paragraph.setAlignment(Element.ALIGN_JUSTIFIED);
            paragraph.setFont(new Font(
                    Font.FontFamily.HELVETICA, 10, Font.NORMAL));

            document.add(paragraph);
        } catch (DocumentException | FileNotFoundException e) {
            e.printStackTrace();
        } finally {
            document.close();
        }
    }
}

Maven Dependencies

<!-- https://search.maven.org/remotecontent?filepath=com/itextpdf/itextpdf/5.5.13.3/itextpdf-5.5.13.3.jar -->
<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13.3</version>
</dependency>

Maven Central

How do I detect non-ASCII characters in string?

By I Wayan Saryada in Core API, IO 0 Comment

The code below detect if a given string has a non ASCII characters in it. We use the CharsetDecoder class from the java.nio package to decode string to be a valid US-ASCII charset.

package org.kodejava.io;

import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharacterCodingException;
import java.nio.CharBuffer;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;

public class NonAsciiValidation {
    public static void main(String[] args) {
        // This string contains a non ASCII character which will produce exception
        // in this program. While the second string has a valid ASCII only characters.
        byte[] invalidBytes = "Copyright © 2021 Kode Java Org".getBytes();
        byte[] validBytes = "Copyright (c) 2021 Kode Java Org".getBytes();

        // Returns a charset object for the named charset.
        CharsetDecoder decoder = StandardCharsets.US_ASCII.newDecoder();
        try {
            CharBuffer buffer = decoder.decode(ByteBuffer.wrap(validBytes));
            System.out.println(Arrays.toString(buffer.array()));

            buffer = decoder.decode(ByteBuffer.wrap(invalidBytes));
            System.out.println(Arrays.toString(buffer.array()));
        } catch (CharacterCodingException e) {
            System.err.println("The information contains a non ASCII character(s).");
            e.printStackTrace();
        }
    }
}

Below is the result of the program:

[C, o, p, y, r, i, g, h, t,  , (, c, ),  , 2, 0, 2, 1,  , K, o, d, e,  , J, a, v, a,  , O, r, g]
The information contains a non ASCII character(s).
java.nio.charset.MalformedInputException: Input length = 1
    at java.base/java.nio.charset.CoderResult.throwException(CoderResult.java:274)
    at java.base/java.nio.charset.CharsetDecoder.decode(CharsetDecoder.java:820)
    at org.kodejava.io.NonAsciiValidation.main(NonAsciiValidation.java:23)