使用外观模式实现教室设备的统一操作，包括上课和下课两个按钮，设备包括电脑、幕布、投影仪、话筒、黑板灯。

首先，我们需要定义一个统一的接口，用于控制教室设备的开关：

public interface ClassroomEquipment {
    void turnOn();
    void turnOff();
}

然后，我们需要定义具体的设备类，实现该接口：

public class Computer implements ClassroomEquipment {
    public void turnOn() {
        System.out.println("Computer is turned on.");
    }
    public void turnOff() {
        System.out.println("Computer is turned off.");
    }
}

public class Projector implements ClassroomEquipment {
    public void turnOn() {
        System.out.println("Projector is turned on.");
    }
    public void turnOff() {
        System.out.println("Projector is turned off.");
    }
}

public class Mic implements ClassroomEquipment {
    public void turnOn() {
        System.out.println("Mic is turned on.");
    }
    public void turnOff() {
        System.out.println("Mic is turned off.");
    }
}

public class BlackboardLight implements ClassroomEquipment {
    public void turnOn() {
        System.out.println("Blackboard light is turned on.");
    }
    public void turnOff() {
        System.out.println("Blackboard light is turned off.");
    }
}

public class Screen implements ClassroomEquipment {
    public void turnOn() {
        System.out.println("Screen is turned on.");
    }
    public void turnOff() {
        System.out.println("Screen is turned off.");
    }
}

接下来，我们需要定义一个外观类，封装这些设备的操作：

public class ClassroomFacade {
    private Computer computer;
    private Projector projector;
    private Mic mic;
    private BlackboardLight blackboardLight;
    private Screen screen;

    public ClassroomFacade() {
        computer = new Computer();
        projector = new Projector();
        mic = new Mic();
        blackboardLight = new BlackboardLight();
        screen = new Screen();
    }

    public void startClass() {
        computer.turnOn();
        projector.turnOn();
        mic.turnOn();
        blackboardLight.turnOn();
        screen.turnOn();
    }

    public void endClass() {
        computer.turnOff();
        projector.turnOff();
        mic.turnOff();
        blackboardLight.turnOff();
        screen.turnOff();
    }
}

最后，我们可以在客户端中使用外观类来控制设备的开关：

public class Client {
    public static void main(String[] args) {
        ClassroomFacade facade = new ClassroomFacade();
        facade.startClass();
        // 上课中...
        facade.endClass();
    }
}

通过外观类的封装，我们可以方便地控制教室设备的开关，而不需要直接操作每个设备。这种设计模式可以简化代码，提高代码的可维护性和可读性。