Field Trip #22

Creating an Excel Spreadsheet with JavaBy Keith Lynn

Java Frame

To contain the contents of the Excel document, we will create a JFrame

A JFrame is a graphical interface It can contains components that hold the data

of the spreadsheet It can also contain a menu bar which gives an

interface to the user

LayoutManager

When we create a JFrame, we can specify how components will be layed out

There are built-in layout managers like FlowLayout which will arrange components in a arow and GridLayout which will arrange components in a grid

We set a layout with setLayout

JMenuItem

We can create a JMenuItem and add it to a JMenu

We can add the JMenu to a JMenuBar We can display the JMenuBar with the method

setMenuBar The Menus appear in the upper left corner

Handling Events

When we select a menu item, it creates an event

In order to detect and act on the event, we attach an ActionListener to the JMenuItem

ActionListener is an interface in the java.awt.event package that contains the method actionPerformed

Interfaces

An interface is a special type of Java program that lists methods

In order to use the interface, we must implement all of the methods in the interface

ActionListener is found in the java.awt.event package

When we attach an ActionListener to a JmenuItem, and select the item, the actionPerformed method is called

We can determine the label of the JmenuItem, we use the method getActionCommand()

Packages

Packages are collections of related classes In order to use the classes in a package, we

can import them into our class It is not necessary to import packages We can use the fully qualified name of the class This is necessary if there are two packages we

are using and there is a class in each package with the same name

Note the import statement is not recursive

CLASSPATH

The CLASSPATH is an environment variable that determines what directories are searched to find a class

Jar files are archive files that contain Java classes

If we want to include a class from a jar file in our class, we place the absolute path of the jar file in the CLASSPATH

POI POI, Poor Obfuscation Interface, is a project

that aims to provide a Java API to read various file formats based on the Office Open XML Standard

In order to read and write Excel documents, we can import the org.apache.poi.xssf.usermodel package

In order to open an Excel document, we create a FileInputStream to open the document

We create an instance of an XSSFWorkbook using the FileInputStream

XSSFWorkbook represents the entire document

Sheets

The XSSFWorkbook is made up of one or more XSSFSheet objects

Each XSSFSheet represents a worksheet The XSSFSheet is composed of XSSFRow

objects Each XSSFRow object is composed of

XSSFCell objects

JTable

To display the information on the JFrame, we will create an instance of a JTable

In order to create the JTable, we need to specify a one dimensional array containing column names and a two dimensional array containing the data

We then access the data of the worksheet and place that information in the JTable

Creating a Chart

To create a new chart, we create a new instance of an XSSFWorkbook

We then create a new XSSFSheet When then create rows and place data in cells We can create a new cell and set its value with

setCellValue

Writing the Spreadsheet

In order to write the spreadsheet, we create an instance of a FileOutputStream attached to a file

After we create the XSSFWorkbook, we call the write method and send the FileOutputStream