Java AWT draws to the screen in a Frame and within it a Canvas or lately, with Swing, within a JFrame and a JPanel. In the program below we create a JFrame (that includes the window title bar) and within this we create a JPanel on which to draw (that doesn't include the window title bar).

A Java graphics context is the environment in which Java's graphics routines operate when drawing to the screen. A Graphics object is responsible for controlling this drawing to the screen within a graphics context. To use it, the Graphics object needs to be passed as a parameter to a paint() (or paintComponent()) method.

The paint() or paintComponent() method is not usually called directly by the programmer. It will be called automatically when the window is created, resized or uncovered. If a programmer wants to force a call to paint() they may do so by calling repaint() which requests an update of the window... and calls paint().

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.imageio.*;

public class ImageDisplayer extends JFrame
{
   public static void main(String[] args)
   {
      new ImageDisplayer();
   }

   ImageDisplayer()
   {
      super("Image Displayer");

      // Set up the window to receive a quit event that closes it
      addWindowListener(new WindowAdapter()
             { public void windowClosing(WindowEvent e) {System.exit(0);} } );
      
      // Set the size of the new JFrame
      setSize (300,300);
      
      // Place a new CanvasImageDisplayer (defined below) in the frame
      add("Center", new PanelImageDisplayer());
      
      // Make the new window visible
      setVisible(true);
   }
}

// Make a subclass of the JPanel
class PanelImageDisplayer extends JPanel
{
   // The paintComponent method of the canvas class is automatically 
   // called when the window is created or resized
   public void paintComponent(Graphics g)
   {
      // Get the dimensions of the JPanel so that if
      // the window is resized we can re-position the image
      Dimension d = getSize();
      int maxX = d.width - 1;
      int maxY = d.height - 1;

      String fileName1 = "tent.GIF";  // Java will read GIFs
      String fileName2 = "tree.PNG";  // Java will read PNGs (and JPEGs) too
      try
      {
         // Try to load an image from the file and display it
         // Note: the origin of the JPanel is the top left corner
         Image image1 = ImageIO.read(new File (fileName1));
         g.drawImage(image1, (int)(maxX*0.3), (int)(maxY*0.3), null);

         Image image2 = ImageIO.read(new File (fileName2));
         g.drawImage(image2, (int)(maxX*0.7), (int)(maxY*0.7), null);
      }
      catch (IOException e)
      {
         System.out.println("ERROR: " + e.getMessage());
      }
   }
}

import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.imageio.*;
import javax.swing.*;

public class VectorDisplayer extends JFrame
{
   public static void main(String[] args)
   {
      new VectorDisplayer();
   }
   
   VectorDisplayer()
   {
      super("Vector Displayer");
      addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } });
      setSize (300, 300);
      add("Center", new PanelVectorDisplayer());
      
      // You can change the cursor over the JFrame as you like... 
      setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
   
      setVisible(true);
   }
}

class PanelVectorDisplayer extends JPanel 
{
   public void paintComponent(Graphics g)
   {
      Dimension d = getSize();
      int maxX = d.width-1;
      int maxY = d.height-1;
    
      g.drawString("d.width = " + d.width, 10, 30);   // write a string to the display
      g.drawString("d.height = " + d.height, 10, 60);
    
      g.setColor(Color.red);                          // set the colour using predefined color objects
      g.drawLine(150, 120, 180, 140);                 // draw lines (start_x, start_y, finish_x, finish_y)
      g.drawLine(180, 140, 120, 140);
      g.drawLine(120, 140, 150, 120);
   
      g.setColor(new Color(120, 95, 200));           // set the colour using a programmer-defined color object
      g.fillRect(130, 140, 40, 30);                  // draw a filled rectangle (start_x, start_y, width, height)
   
      g.setColor(Color.green);
      g.drawLine(100, 170, 200, 170);
   }
}

import java.awt.*;
import java.io.*;
import javax.imageio.*;
import java.awt.image.*; // import the names of the image classes

public class ImageSaver
{
   public static void main(String[] args) throws IOException
   {
      int size = 300;
      
      // Create space in which to store some pixels (a buffered image)
      // and create something into which to draw 2D graphics to place in the BufferedImage.
      // Graphics2D is a subclass of the basic Graphics class that provides extra functionality.
      BufferedImage image = new BufferedImage(size, size, BufferedImage.TYPE_INT_ARGB);
      Graphics2D g = image.createGraphics();

      // Draw the house picture into the graphics object
      g.setColor(Color.red);
      g.drawLine(150, 120, 180, 140);
      g.drawLine(180, 140, 120, 140);
      g.drawLine(120, 140, 150, 120);
   
      g.setColor(new Color(120, 95, 200));
      g.fillRect(130, 140, 40, 30);
   
      g.setColor(Color.green);
      g.drawLine(100, 170, 200, 170);
   
      // Save the image using the ImageIO routines into a png file
      File file = new File("ImageSaved.png");
      ImageIO.write(image, "png", file);
   
      System.out.println("Saved image: " + file);
   }
}