Accessing object through variable in JAVA for Window based application

So, I am developing a GUI based application that reads data from Excel using Apache POI and displays it using JAVA AWT/SWING based Window Application. So, to start with I have integrated Apache POI in GUI based JAVA project.

So, now I am trying to access a particular cell data from excel and print it in the GUI App.
I have sorted out how to get particular cell data from excel to Java and how to use Jlabel. To proceed it with I need to send the cell data to JLabel.

I have done the following to get Cell data: Clearly, we have cell object from Cell class. How do I send this cell data to JLabel?

I have the following code for JLabel.

try (InputStream inp = new FileInputStream("C:\\Users\\mohin\\OneDrive\\Desktop\\a.xlsx")) {  
            Workbook wb = WorkbookFactory.create(inp);  
            Sheet sheet = wb.getSheetAt(0);  
            Row row = sheet.getRow(2);  
            Cell cell = row.getCell(2);
            if (cell != null)  
                System.out.println("Data: "+cell);  
            else  
                System.out.println("Cell is empty");  
    }catch(Exception e) {  
        System.out.println(e);  
    } 

Clearly we have cell object from Cell class. How do I send this cell data to JLable?

I have the following code for JLable.

Here after we press the button the content of the Lable changes.

lblNewLabel = new JLabel("Hey there. Your GPA is");
		lblNewLabel.setFont(new Font("Tahoma", Font.PLAIN, 18));
		lblNewLabel.setBounds(100, 46, 298, 55);
		frame.getContentPane().add(lblNewLabel);


JButton btnNewButton = new JButton("Show me!");
		btnNewButton.setForeground(Color.BLUE);
		btnNewButton.setFont(new Font("Microsoft YaHei UI", Font.BOLD, 16));
		btnNewButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				//JOptionPane.showMessageDialog(null, "Hello World!");
				lblNewLabel.setText(cell);
			}
		});

lblNewLabel.setText(cell);

But it's showing error. I even declared a new string and passed it using cell object. But it didn't work either.

I am looking for a way to pass the output from Cell to JLabel.

Both are in the main function only.

Below is the entire code.

package com;

import java.io.FileInputStream;  
import java.io.InputStream;  
import org.apache.poi.ss.usermodel.Cell;  
import org.apache.poi.ss.usermodel.Row;  
import org.apache.poi.ss.usermodel.Sheet;  
import org.apache.poi.ss.usermodel.Workbook;  
import org.apache.poi.ss.usermodel.WorkbookFactory;  
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.Font;
import java.awt.Color;
import javax.swing.JTextField;
import javax.swing.JLabel;

public class GUI {

	private JFrame frame;
	private JLabel lblNewLabel;
	private JTextField textField;
	private JTextField textField_1;
	private JLabel lblNewLabel_1;
	private JTextField textField_2;
	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		try (InputStream inp = new FileInputStream("C:\\Users\\mohin\\OneDrive\\Desktop\\a.xlsx")) {  
            Workbook wb = WorkbookFactory.create(inp);  
            Sheet sheet = wb.getSheetAt(0);  
            Row row = sheet.getRow(2);  
            Cell cell = row.getCell(2);
            if (cell != null)  
                System.out.println("Data: "+cell);  
            else  
                System.out.println("Cell is empty");  
    }catch(Exception e) {  
        System.out.println(e);  
    }  
		
		
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					GUI window = new GUI();
					window.frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the application.
	 */
	public GUI() {
		initialize();
	}

	/**
	 * Initialize the contents of the frame.
	 */
	private void initialize() {
		frame = new JFrame();
		frame.setBounds(100, 100, 605, 418);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.getContentPane().setLayout(null);
		
		JButton btnNewButton = new JButton("Show me!");
		btnNewButton.setForeground(Color.BLUE);
		btnNewButton.setFont(new Font("Microsoft YaHei UI", Font.BOLD, 16));
		btnNewButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				//JOptionPane.showMessageDialog(null, "Hello World!");
				lblNewLabel.setText(cell);
			}
		});
		btnNewButton.setBounds(147, 133, 130, 31);
		frame.getContentPane().add(btnNewButton);
		
		lblNewLabel = new JLabel("Hey there. Your GPA is");
		lblNewLabel.setFont(new Font("Tahoma", Font.PLAIN, 18));
		lblNewLabel.setBounds(100, 46, 298, 55);
		frame.getContentPane().add(lblNewLabel);
		
		textField = new JTextField();
		textField.setBounds(63, 214, 96, 19);
		frame.getContentPane().add(textField);
		textField.setColumns(10);
		
		textField_1 = new JTextField();
		textField_1.setBounds(342, 214, 96, 19);
		frame.getContentPane().add(textField_1);
		textField_1.setColumns(10);
		
		lblNewLabel_1 = new JLabel("Answer-");
		lblNewLabel_1.setFont(new Font("Tahoma", Font.PLAIN, 24));
		lblNewLabel_1.setBounds(139, 323, 122, 48);
		frame.getContentPane().add(lblNewLabel_1);
		
		textField_2 = new JTextField();
		textField_2.setBounds(301, 329, 174, 42);
		frame.getContentPane().add(textField_2);
		textField_2.setColumns(10);
		
		JButton btnNewButton_1 = new JButton("Multiply");
		btnNewButton_1.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				int a,b,ans;
				try {
					a=Integer.parseInt(textField.getText());
					b=Integer.parseInt(textField_1.getText());
					ans=a*b;
					textField_2.setText(Integer.toString(ans));
					
				}catch(Exception e1) {
					JOptionPane.showMessageDialog(null,"Enter valid number");
				}
			}
		});
		btnNewButton_1.setBounds(90, 264, 85, 21);
		frame.getContentPane().add(btnNewButton_1);
		
		JButton btnNewButton_2 = new JButton("Divide");
		btnNewButton_2.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				int a,b,ans;
				try {
					a=Integer.parseInt(textField.getText());
					b=Integer.parseInt(textField_1.getText());
					ans=a/b;
					textField_2.setText(Integer.toString(ans));
					
				}catch(Exception e2) {
					JOptionPane.showMessageDialog(null,"Enter valid number");
				}
			}
		});
		
		btnNewButton_2.setBounds(330, 264, 85, 21);
		frame.getContentPane().add(btnNewButton_2);
	}
}

Don't mind all other GUI code. They are just some bunch of buttons, text fields.

First you need to get the Cell cell in the scope of the initialize method or the Cell cell would must be a class member as JLabel lblNewLabel also is.

Another solution would be having a public method to get the cell content from the workbook which then can be called from within the initialize method.

Then, the setText method of a JLabel needs a String as the parameter. So you need converting the content of the cell to String.

So simplest solution would be

...
String cellContent = cell.toString();
...

But that is not the preferred way to do it. Instead do using DataFormatter of apache poi to get the cell content out of the Cell as a String. DataFormatter will get that String the same as Excel shows the cell content.

...
DataFormatter formatter = new DataFormatter();
...
String cellContent = formatter.formatCellValue(cell);
...

If there can be formula cells and you need the formula results instead of the formulas, then you will need FormulaEvaluator additionally.

...
DataFormatter formatter = new DataFormatter();
FormulaEvaluator evaluator = wb.getCreationHelper().createFormulaEvaluator();
...
String cellContent = formatter.formatCellValue(cell, evaluator);
...

So to extend your code you could have following method:

...
public String getCellContent() {
 String cellContent = "";
 try (InputStream inp = new FileInputStream("C:\\Users\\mohin\\OneDrive\\Desktop\\a.xlsx"); 
      Workbook wb = WorkbookFactory.create(inp)) {  
  DataFormatter formatter = new DataFormatter();
  FormulaEvaluator evaluator = wb.getCreationHelper().createFormulaEvaluator();
  Sheet sheet = wb.getSheetAt(0);  
  Row row = sheet.getRow(2);
  Cell cell = null;
  if (row != null) cell = row.getCell(2);
  cellContent = formatter.formatCellValue(cell, evaluator);
 } catch (Exception e) {
  e.printStackTrace();
 }
 return cellContent;
}
...

And then in your initialize method:

...
            public void actionPerformed(ActionEvent e) {
                //JOptionPane.showMessageDialog(null, "Hello World!");
                lblNewLabel.setText(getCellContent());
            }
...

But of course this will always get the same cell content from the sheet. So for practical usage the getCellContent would must have parameters to tell what concrete cell shall be read. And then the method should not open the workbook every single time a cell content shall got. So Workbook wb, DataFormatter formatter and FormulaEvaluator evaluator should be class members and created only once while initialize.

You are trying to access cell, but it is defined in another scope.
You could create method, which returns the cell-string.

public String getCell() {
        try (InputStream inp = new FileInputStream("C:\\Users\\mohin\\OneDrive\\Desktop\\a.xlsx")) {  
        Workbook wb = WorkbookFactory.create(inp);  
        Sheet sheet = wb.getSheetAt(0);  
        Row row = sheet.getRow(2);  
        Cell cell = row.getCell(2);
        if (cell != null)  
            return cell.toString(); 
}catch(Exception e) {  
    System.out.println(e);  
}  

return null;
}
and then access it like so:

JButton btnNewButton = new JButton("Show me!");
    btnNewButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            //JOptionPane.showMessageDialog(null, "Hello World!");
            lblNewLabel.setText(getCell());
        }
    });