尝试在MVC示例中使用Java lambda表达式，don'；I don’我不知道我还能做什么？

下面的MVC示例来自Head First Design Patterns一书。

此MVC示例关注观察者模式（模型与视图/控制器之间） 策略模式（控制器为策略）。

今天我想尝试使用lambda表达式来改进代码， 我只能将视图中的Actionperformed部分更改为lambda表达式。

我不知道在本例中是否还有更多地方可以使用lambda表达式？

示例的开头

型号零件：
主题：

public interface BeatModelInterface {
    void initialize();

    void on();

    void off();

    void setBPM(int bpm);

    int getBPM();

    void registerObserver(BeatObserver o);

    void removeObserver(BeatObserver o);

    void registerObserver(BPMObserver o);

    void removeObserver(BPMObserver o);
}

public interface BeatObserver {
    void updateBeat();
}
public interface BPMObserver {
    void updateBPM();
}

import javax.sound.midi.*;

import java.util.*;

public class BeatModel implements BeatModelInterface, MetaEventListener {
    Sequencer sequencer;
    ArrayList<BeatObserver> beatObservers = new ArrayList<BeatObserver>();

    ArrayList<BPMObserver> bpmObservers = new ArrayList<BPMObserver>();
    int bpm = 90;
    Sequence sequence;
    Track track;

    public void initialize() {
        setUpMidi(); 
        buildTrackAndStart();
    }

    public void on() {
        System.out.println("Starting the sequencer");
        sequencer.start();
        setBPM(90);
    }

    public void off() {
        setBPM(0);
        sequencer.stop(); 
    }

    public void setBPM(int bpm) {
        this.bpm = bpm;   
        sequencer.setTempoInBPM(getBPM()); 
        notifyBPMObservers();  
    }

    public int getBPM() {
        return bpm;
    }

    void beatEvent() {
        notifyBeatObservers();
    }


    public void registerObserver(BeatObserver o) {
        beatObservers.add(o);
    }

    public void notifyBeatObservers() {
        for(int i = 0; i < beatObservers.size(); i++) {
            BeatObserver observer = (BeatObserver)beatObservers.get(i);
            observer.updateBeat();
        }
    }

    public void registerObserver(BPMObserver o) {
        bpmObservers.add(o);
    }

    public void notifyBPMObservers() {
        for(int i = 0; i < bpmObservers.size(); i++) {
            BPMObserver observer = (BPMObserver)bpmObservers.get(i);
            observer.updateBPM();
        }
    }


    public void removeObserver(BeatObserver o) {
        int i = beatObservers.indexOf(o);
        if (i >= 0) {
            beatObservers.remove(i);
        }
    }



    public void removeObserver(BPMObserver o) {
        int i = bpmObservers.indexOf(o);
        if (i >= 0) {
            bpmObservers.remove(i);
        }
    }


    public void meta(MetaMessage message) {
        if (message.getType() == 47) {
            beatEvent();
            sequencer.start();
            setBPM(getBPM());
        }
    }


    public void setUpMidi() {
        try {
            sequencer = MidiSystem.getSequencer();
            sequencer.open();
            sequencer.addMetaEventListener(this);
            sequence = new Sequence(Sequence.PPQ,4);
            track = sequence.createTrack();
            sequencer.setTempoInBPM(getBPM());
            sequencer.setLoopCount(Sequencer.LOOP_CONTINUOUSLY);
        } catch(Exception e) {
            e.printStackTrace();
        }
    } 

    public void buildTrackAndStart() {
        int[] trackList = {35, 0, 46, 0};

        sequence.deleteTrack(null);
        track = sequence.createTrack();

        makeTracks(trackList);
        track.add(makeEvent(192,9,1,0,4));      
        try {
            sequencer.setSequence(sequence);                    
        } catch(Exception e) {
            e.printStackTrace();
        }
    } 

    public void makeTracks(int[] list) {        

        for (int i = 0; i < list.length; i++) {
            int key = list[i];

            if (key != 0) {
                track.add(makeEvent(144,9,key, 100, i));
                track.add(makeEvent(128,9,key, 100, i+1));
            }
        }
    }

    public  MidiEvent makeEvent(int comd, int chan, int one, int two, int tick) {
        MidiEvent event = null;
        try {
            ShortMessage a = new ShortMessage();
            a.setMessage(comd, chan, one, two);
            event = new MidiEvent(a, tick);

        } catch(Exception e) {
            e.printStackTrace(); 
        }
        return event;
    }
        }

具体主题：

public interface BeatModelInterface {
    void initialize();

    void on();

    void off();

    void setBPM(int bpm);

    int getBPM();

    void registerObserver(BeatObserver o);

    void removeObserver(BeatObserver o);

    void registerObserver(BPMObserver o);

    void removeObserver(BPMObserver o);
}

public interface BeatObserver {
    void updateBeat();
}
public interface BPMObserver {
    void updateBPM();
}

import javax.sound.midi.*;

import java.util.*;

public class BeatModel implements BeatModelInterface, MetaEventListener {
    Sequencer sequencer;
    ArrayList<BeatObserver> beatObservers = new ArrayList<BeatObserver>();

    ArrayList<BPMObserver> bpmObservers = new ArrayList<BPMObserver>();
    int bpm = 90;
    Sequence sequence;
    Track track;

    public void initialize() {
        setUpMidi(); 
        buildTrackAndStart();
    }

    public void on() {
        System.out.println("Starting the sequencer");
        sequencer.start();
        setBPM(90);
    }

    public void off() {
        setBPM(0);
        sequencer.stop(); 
    }

    public void setBPM(int bpm) {
        this.bpm = bpm;   
        sequencer.setTempoInBPM(getBPM()); 
        notifyBPMObservers();  
    }

    public int getBPM() {
        return bpm;
    }

    void beatEvent() {
        notifyBeatObservers();
    }


    public void registerObserver(BeatObserver o) {
        beatObservers.add(o);
    }

    public void notifyBeatObservers() {
        for(int i = 0; i < beatObservers.size(); i++) {
            BeatObserver observer = (BeatObserver)beatObservers.get(i);
            observer.updateBeat();
        }
    }

    public void registerObserver(BPMObserver o) {
        bpmObservers.add(o);
    }

    public void notifyBPMObservers() {
        for(int i = 0; i < bpmObservers.size(); i++) {
            BPMObserver observer = (BPMObserver)bpmObservers.get(i);
            observer.updateBPM();
        }
    }


    public void removeObserver(BeatObserver o) {
        int i = beatObservers.indexOf(o);
        if (i >= 0) {
            beatObservers.remove(i);
        }
    }



    public void removeObserver(BPMObserver o) {
        int i = bpmObservers.indexOf(o);
        if (i >= 0) {
            bpmObservers.remove(i);
        }
    }


    public void meta(MetaMessage message) {
        if (message.getType() == 47) {
            beatEvent();
            sequencer.start();
            setBPM(getBPM());
        }
    }


    public void setUpMidi() {
        try {
            sequencer = MidiSystem.getSequencer();
            sequencer.open();
            sequencer.addMetaEventListener(this);
            sequence = new Sequence(Sequence.PPQ,4);
            track = sequence.createTrack();
            sequencer.setTempoInBPM(getBPM());
            sequencer.setLoopCount(Sequencer.LOOP_CONTINUOUSLY);
        } catch(Exception e) {
            e.printStackTrace();
        }
    } 

    public void buildTrackAndStart() {
        int[] trackList = {35, 0, 46, 0};

        sequence.deleteTrack(null);
        track = sequence.createTrack();

        makeTracks(trackList);
        track.add(makeEvent(192,9,1,0,4));      
        try {
            sequencer.setSequence(sequence);                    
        } catch(Exception e) {
            e.printStackTrace();
        }
    } 

    public void makeTracks(int[] list) {        

        for (int i = 0; i < list.length; i++) {
            int key = list[i];

            if (key != 0) {
                track.add(makeEvent(144,9,key, 100, i));
                track.add(makeEvent(128,9,key, 100, i+1));
            }
        }
    }

    public  MidiEvent makeEvent(int comd, int chan, int one, int two, int tick) {
        MidiEvent event = null;
        try {
            ShortMessage a = new ShortMessage();
            a.setMessage(comd, chan, one, two);
            event = new MidiEvent(a, tick);

        } catch(Exception e) {
            e.printStackTrace(); 
        }
        return event;
    }
        }

实施战略：

public class BeatController implements ControllerInterface {
    BeatModelInterface model; 
    DJView view;

    public BeatController(BeatModelInterface model) {
        this.model = model;
        view = new DJView(this, model);  
        view.createView();
        view.createControls();
        view.disableStopMenuItem();
        view.enableStartMenuItem();
        model.initialize();
    }

    public void start() {                  
        model.on();
        view.disableStartMenuItem();    
        view.enableStopMenuItem();
    }

    public void stop() {
        model.off();
        view.disableStopMenuItem();
        view.enableStartMenuItem();
    }

    public void increaseBPM() {
        int bpm = model.getBPM();
        model.setBPM(bpm + 1);
    }

    public void decreaseBPM() {
        int bpm = model.getBPM();
        model.setBPM(bpm - 1);
    }

    public void setBPM(int bpm) {   
        model.setBPM(bpm);
    }
}

最后我们将MVC结合在一起：

public class DJTestDrive {

    public static void main (String[] args) {
        BeatModelInterface model = new BeatModel();
    ControllerInterface controller = new BeatController(model);      
    }
}

----示例的结尾-----
问题：

我只能将视图中的actionperformed部分更改为lambda表达式，如下所示：
原件：

        menuBar = new JMenuBar();
        menu = new JMenu("DJ Control");
        startMenuItem = new JMenuItem("Start");
        menu.add(startMenuItem);
        startMenuItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                controller.start();
            }
        });
        stopMenuItem = new JMenuItem("Stop");
        menu.add(stopMenuItem); 
        stopMenuItem.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                controller.stop();
            }
        });
        JMenuItem exit = new JMenuItem("Quit");
        exit.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                System.exit(0);
            }
        });

到lambda表达式：

        menuBar = new JMenuBar();
        menu = new JMenu("DJ Control");
        startMenuItem = new JMenuItem("Start");
        menu.add(startMenuItem);
        startMenuItem.addActionListener((ActionEvent event) -> {
            controller.start();
        });
        stopMenuItem = new JMenuItem("Stop");
        menu.add(stopMenuItem); 
        stopMenuItem.addActionListener((ActionEvent event) -> {
            controller.stop();
        });
        JMenuItem exit = new JMenuItem("Quit");
        exit.addActionListener((ActionEvent event) -> {
            System.exit(0);
        });   

在这种复杂的示例中，还有其他地方可以使用lambda表达式吗？或者我不应该在这样复杂的情况下使用lambda表达式

---

非常感谢您的耐心

在lambda中，参数的类型不是强制性的，括号是可选的，因为只声明了一个参数。因此您可以编写

startMenuItem.addActionListener（事件->{controller.start（）；}）

@davidxxx非常感谢您的建议：）如果您认为本例中有更多地方我可以换成lambda，请随时通知我。我是这个领域的新手，我会非常感谢你的帮助！提示：一般来说，当您的接口只包含一个方法时，它是一个功能接口（可以注释为

@functioninterface

），基本上可以与lambda互换使用。@Joel非常感谢您的提示！因此，在这个包含多个方法的多个接口的复杂示例中，我不应该使用lambda，对吗？@YSL这不是我的意思-您可以随时使用lambda（或者说：随时编译）。实际上，乍一看，我认为您的

BeatObserver

/

BPMObserver

可以被视为功能接口，但考虑到它们的实现方式，这是不正确的