2.设计模式用例(一)

1. 工厂模式: 根据不同的歌手，生产出对应的歌。歌手是Visitor, 歌曲是Acceptor

package designPattern;

import static designPattern.Cast.JIANG_DA_WEI;
import static designPattern.Cast.XIAO_YUE_YUE;

enum Cast {
    XIAO_YUE_YUE, JIANG_DA_WEI;
}

interface Song {
    void showLyric();
}

class WuHuan implements Song {
    @Override
    public void showLyric() {
        System.out.println("啊~啊~~啊~五环，你比四环多一环");
    }
}

class MuDan implements Song {
    @Override
    public void showLyric() {
        System.out.println("啊~啊~~啊~牡丹，百花丛中最鲜艳");
    }
}

class SongFactory {
    Song getSong(Cast cast) {
        switch (cast) {
            case XIAO_YUE_YUE: return new WuHuan();
            case JIANG_DA_WEI: return new MuDan();
            default: return null;
        }
    }
}


public class FactoryStudy {
    public static void main(String[] args) {
        SongFactory songFactory = new SongFactory();
        Song wuHuan = songFactory.getSong(XIAO_YUE_YUE);
        Song mudan = songFactory.getSong(JIANG_DA_WEI);
        wuHuan.showLyric();
        mudan.showLyric();
    }
}
/// result
// 啊~啊~~啊~五环，你比四环多一环
// 啊~啊~~啊~牡丹，百花丛中最鲜艳

2. 访问者模式: Visitor 访问 不同的Element会有不同的操作 (添加了对象结构)

public interface Element {
    void accept(Visitor visitor);
}

public interface Visitor {
    void visit(Student student);
    void visit(Programmer programmer);
}

public class Student implements Element {
    private int score;
    private String name;

    public Student(int score, String name) {
        this.score = score;
        this.name = name;
    }

    public void accept(Visitor visitor) {
        visitor.visit(this);
    }

    public int getScore() {
        return score;
    }

    public String getName() {
        return name;
    }
}

public class Programmer implements Element {
    private int codeQuality;
    private String name;

    public Programmer(int codeQuality, String name) {
        this.codeQuality = codeQuality;
        this.name = name;
    }

    public void accept(Visitor visitor) {
        visitor.visit(this);
    }

    public int getCodeQuality() {
        return codeQuality;
    }

    public String getName() {
        return name;
    }
}

public class Critics implements Visitor {
    public void visit(Programmer programmer) {
        if (programmer.getCodeQuality() > 80) {
            System.out.println(programmer.getName() + " is a good programmer");
        } else {
            System.out.println(programmer.getName() + " is a bad programmer");
        }
    }

    public void visit(Student student) {
        if (student.getScore() > 80) {
            System.out.println(student.getName() + " is a good student");
        } else {
            System.out.println(student.getName() + " is a bad student");
        }
    }
}


public class ObjectStructure {
    private List<Element> elements = new ArrayList<>();
    public void accept(Visitor visitor) {
        for (Element element: elements) {
            element.accept(visitor);
        }
    }

    public void addElement(Element element) {
        elements.add(element);
    }
}

public class VisitorStudy {
    public static void main(String[] args) {
        ObjectStructure objectStructure = new ObjectStructure();
        objectStructure.addElement(new Student(50, "S1"));
        objectStructure.addElement(new Programmer(50, "P1"));
        objectStructure.addElement(new Student(80, "S2"));
        objectStructure.addElement(new Programmer(90, "P2"));
        objectStructure.addElement(new Student(90, "S3"));

        Critics critics = new Critics();
        objectStructure.accept(critics);
    }
}
/// output
// S1 is a bad student
// P1 is a bad programmer
// S2 is a bad student
// P2 is a good programmer
// S3 is a good student

3. 适配器模式

/**
 * 目标操作是 keyDown
 * 物理键盘能直接实现 按键的功能，而触屏只有tap的功能
 * 这时候创建一个触屏的Adapter，由Adapter实现keyDown的功能
 */
interface InputTool {
    void keyDown(String s);
}

class Keyboard implements InputTool{
    public void keyDown(String key) {
        System.out.println("Keyboard: Key " + key + " is pressed");
    }
}

class VirtualKeyboard {
    void tap(String s) {
        System.out.println("Phone: key " + s + " is touched");
    }
}

class VirtualKeyBoardAdapter implements InputTool {
    private VirtualKeyboard virtualKeyboard;

    VirtualKeyBoardAdapter(VirtualKeyboard virtualKeyboard) {
        this.virtualKeyboard = virtualKeyboard;
    }

    @Override
    public void keyDown(String s) {
        virtualKeyboard.tap(s);
    }
}

public class AdapterStudy {
    public static void main(String[] args) {
        InputTool inputTool = new VirtualKeyBoardAdapter(new VirtualKeyboard());
        inputTool.keyDown("1");
    }
}

4.享元模式

package designPattern;

import java.util.HashMap;

/**
 * make a guitar tab reader (guitar score)
 * The Note on each string will be saved into a hash map, whose key is the string's label (EADGBE)
 * When the string is plucked for the second time, the note will be retrieved from the hashmap instead of the constructor
 */
enum GuitarString {
    L_E, A, D, G, B, H_E
}
class TabNote {
    private GuitarString guitarString;
    private int fret;

    public GuitarString getGuitarString() {
        return guitarString;
    }

    public void setGuitarString(GuitarString guitarString) {
        this.guitarString = guitarString;
    }

    public int getFret() {
        return fret;
    }

    public void setFret(int fret) {
        this.fret = fret;
    }

    public void playSound() {
        System.out.println("Plays " + guitarString.name() + " string, fret " + fret + "~~ ");
    }
}

class TabNoteProvider {
    HashMap<GuitarString, TabNote> notePool = new HashMap<>();
    TabNote getNote(GuitarString s, int fret) {
        TabNote note;
        if (notePool.containsKey(s)) {
            note = notePool.get(s);
            note.setFret(fret);
        } else {
            note = new TabNote();
            note.setFret(fret);
            note.setGuitarString(s);
            notePool.put(note.getGuitarString(), note);
        }
        return note;
    }
}

public class FlyWeightStudy {
    public static void main(String[] args) {
        //there are 7 notes, but only two TabNote objects are created with the help of the hash map
        TabNoteProvider provider = new TabNoteProvider();
        provider.getNote(GuitarString.A, 3).playSound();
        provider.getNote(GuitarString.A, 3).playSound();
        provider.getNote(GuitarString.G, 0).playSound();
        provider.getNote(GuitarString.G, 0).playSound();
        provider.getNote(GuitarString.G, 2).playSound();
        provider.getNote(GuitarString.G, 2).playSound();
        provider.getNote(GuitarString.G, 0).playSound();
    }
}