Como inserir imagens num programa em java

// Fetch icon
    Icon icon = new ImageIcon("icon.gif");
    
    // Create a label with text and an icon; the icon appears to the left of the text
    JLabel label = new JLabel("Text Label", icon, JLabel.CENTER);
    
    // Create a label with only an icon
    label = new JLabel(icon);

This example adds or replaces the icon in an existing JLabel component: 
    // Add an icon to an existing label
    label.setIcon(icon);