I am unable to post a picture with this post, so can you just try the code out yourself.
I want an image of a triangle to take up the whole bottom of my GUI.
How would I go about doing this?
Here is the code:

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

public class TriangleCalculator extends JFrame{

private JLabel sideALabel, sideBLabel, sideCLabel, triangleImage;
private JTextField sideAInput,sideBInput, sideCInput;
private JRadioButton sideAOption, sideBOption, sideCOption;
private JButton calculateButton, clearButton;
private JPanel buttonPane, mainPanel;
private GridBagConstraints gbc;

public TriangleCalculator(){
super("TriangleCalculator");
addComponents();
setSize(350, 500);
setResizable(false);
setVisible(true);

}

public void addComponents()
{
gbc = new GridBagConstraints();

sideALabel = new JLabel("Enter the value of side A: ");
sideBLabel = new JLabel("Enter the value of side B: ");
sideCLabel = new JLabel("Enter the value of side C: ");

sideAInput = new JTextField(10);
sideBInput = new JTextField(10);
sideCInput = new JTextField(10);

sideAOption = new JRadioButton();
sideBOption = new JRadioButton();
sideCOption = new JRadioButton();

calculateButton = new JButton("Calculate");
clearButton = new JButton("Clear");

buttonPane = new JPanel(new GridLayout(0, 2));
mainPanel = new JPanel();
add(buttonPane, BorderLayout.SOUTH);
add(mainPanel, BorderLayout.CENTER);

gbc.gridx = 0;
gbc.gridy = 0;
mainPanel.add(sideALabel, gbc);

gbc.gridx = 1;
gbc.gridy = 0;
mainPanel.add(sideAInput, gbc);

gbc.gridx = 2;
gbc.gridy = 0;
mainPanel.add(sideAOption);

gbc.gridx = 1;
gbc.gridy = 1;
mainPanel.add(sideBLabel, gbc);

gbc.gridx = 1;
gbc.gridy = 1;
mainPanel.add(sideBInput, gbc);

gbc.gridx = 2;
gbc.gridy = 1;
mainPanel.add(sideBOption);

gbc.gridx = 0;
gbc.gridy = 2;
mainPanel.add(sideCLabel, gbc);

gbc.gridx = 1;
gbc.gridy = 2;
mainPanel.add(sideCInput, gbc);

gbc.gridx = 2;
gbc.gridy = 3;
mainPanel.add(sideCOption);

buttonPane.add(clearButton);
buttonPane.add(calculateButton);

}


}