Understandnig Java Inner Classes

Member Inner Classes

public class ComputerSystem {
    private String systemName = "Desktop";
    
    private void displayMessage() {
        System.out.println("This is a computer system");
    }
    
    class HardwareComponent {
        String memory = "32GB";
        String storage = "SSD";
        
        void showDetails() {
            System.out.println(systemName);
            displayMessage();
        }
    }
}

public class Application {
    public static void main(String[] args) {
        ComputerSystem system = new ComputerSystem();
        ComputerSystem.HardwareComponent component = system.new HardwareComponent();
        component.showDetails();
    }
}

Static Nested Classes

public class ComputerSystem {
    private static String manufacturer = "TechCorp";
    private String systemName = "Desktop";
    
    private void displayMessage() {
        System.out.println("This is a computer system");
    }
    
    static class Peripheral {
        String display = "LED";
        
        void showInfo() {
            System.out.println(manufacturer);
        }
    }
}

// Usage
ComputerSystem.Peripheral peripheral = new ComputerSystem.Peripheral();

Local Inner Classes

public class ComputerSystem {
    int processData(int value) {
        class LocalComponent {
            String brandA = "Dell";
            String brandB = "HP";
        }
        
        LocalComponent component = new LocalComponent();
        return value * 2;
    }
}

Anoynmous Inner Classes

// Implementing interface with anonymous class
new DeviceOperation() {
    @Override
    public void powerOn() {
        System.out.println("Device powered on");
    }
    
    @Override
    public void powerOff() {
        System.out.println("Device powered off");
    }
    
    @Override
    public void restart() {
        System.out.println("Device restarting");
    }
};

public interface DeviceOperation {
    void powerOn();
    void powerOff();
    void restart();
}