《設(shè)計(jì)模式之美》(二：創(chuàng)造型模式)

單例模式
- 餓漢式
- 懶漢式:雙重校驗(yàn)->volatile 在jdk版本較低，禁止指令排序
- 內(nèi)部類
- 枚舉

單例的劣勢
1. 繼承、多態(tài)支持的不友好
2. 隱藏依賴關(guān)系
3. 擴(kuò)展性不好（比如要?jiǎng)?chuàng)建兩個(gè)對象）
4. 測試不友好
5. 不支持參數(shù)的構(gòu)造函數(shù)
先調(diào)用 init(paramA,paramB) 再調(diào)用 getInstance()
getInstance(paramA,paramB),有問題
配置靜態(tài)參數(shù)

線程單例
進(jìn)程單例：一般默認(rèn)方式
集群單例:多個(gè)進(jìn)程也是單例---->加鎖 回寫 釋放鎖 外部共享存儲區(qū)(比如文件)

code
//餓漢
public class A {
    private static A instance = new A();

    private A() {
    }

    public static A getInstance() {
        return instance;
    }
}

//懶漢
public class A {
    private static A instance ;
    
    public static A getInstance() {
        if (instance == null){
            synchronized (A.class){
                if (instance == null){
                    instance = new A();
                }
            }
        }
        return instance;
    }
}

//枚舉
public enum A {
    ONE(1),TWO(2),THREE(3),FOUR(4),FIVE(5);

    private int value;
    A(int i) {
        this.value = i;
    }
    public int getValue() {
        return value;
    }
}

//靜態(tài)內(nèi)部類
public class A {
    
    private static class B{
        private static A instance = new A();
    }

    public static A getInstance() {
        return B.instance;
    }
}

工廠

簡單工廠
工廠方法：在構(gòu)造對象比較復(fù)雜的時(shí)候味廊，工廠里創(chuàng)建工廠

DI:解析配置文件痹雅，工廠類創(chuàng)建對象(反射)

code
public interface IParseConfig {
    void parse(String input);
}
public class XMLParse implements IParseConfig {
    @Override
    public void parse(String input) {
        //xml 解析
    }
}

public class JsonParse implements IParseConfig {
    @Override
    public void parse(String input) {
        //Json 解析
    }
}

public class PropertyParse implements IParseConfig {
    @Override
    public void parse(String input) {
        //properties 解析
    }
}

public class ParseFactory {

    private static final HashMap<String,IParseConfig> cacheParse = new HashMap<>();
    static {
        cacheParse.put("json",new JsonParse());
        cacheParse.put("xml",new XMLParse());
        cacheParse.put("properties",new PropertyParse());
    }

    public  void parse(String filePath){
        //簡單工廠
        String fileExtension = getFileExtension(filePath);
        String input = "解析出來的文件流";
        IParseConfig parseConfig;
        if ("json".equals(fileExtension)){
            parseConfig = new JsonParse();
        }else if ("xml".equals(fileExtension)){
            parseConfig = new XMLParse();
        }else if ("properties".equals(fileExtension)){
            parseConfig = new PropertyParse();
        }else {
            throw new UnsupportedOperationException("UnSupport format");
        }
        parseConfig.parse(input);

        //節(jié)省創(chuàng)建時(shí)間 直接在緩存拿出來
        IParseConfig parseConfig1 = cacheParse.get(fileExtension);
        parseConfig1.parse(input);

        //工廠方法
        IParseFactory parseFactory;
        if ("json".equals(fileExtension)){
            parseFactory = new JsonParseFactory();
        }else if ("xml".equals(fileExtension)){
            parseFactory = new XMLParseFactory();
        }else if ("properties".equals(fileExtension)){
            parseFactory = new PropertyParseFactory();
        }else {
            throw new UnsupportedOperationException("UnSupport format");
        }
        parseConfig =  parseFactory.createParse();
        parseConfig.parse(input);

    }

    private String getFileExtension(String filePath){
        return "json";
    }
}

//xml properties相似 省略
public class JsonParseFactory implements IParseFactory {
    @Override
    public IParseConfig createParse() {
        return new JsonParse();
    }
}

//抽象工廠 工廠創(chuàng)建多個(gè)實(shí)例
public interface IConfigParseFactory {
    IParseFactory createRuleParser();
    ISystemFactory createSystemParser();
}

建造者模式

如果必填參數(shù)比較多，通過構(gòu)造函數(shù)不是很合適
各個(gè)參數(shù)有依賴關(guān)系，通過set不太好檢驗(yàn)
如果有需求臀规，對象創(chuàng)建之后，各個(gè)屬性不可變

public class Dialog {
    private String title;
    private int width;
    private int height;


    private Dialog(Builder builder) {
        title = builder.title;
        width = builder.width;
        height = builder.height;
    }

    public static class Builder{
        private  String title;
        private  int width;
        private  int height;

        public Builder setWidth(int width){
            if (width < 0){
                throw new UnsupportedOperationException("width should >= 0");
            }
            this.width = width;
            return Builder.this;
        }

        public Builder setHeight(int height){
            if (height < 0){
                throw new UnsupportedOperationException("width should >= 0");
            }
            this.height = height;
            return Builder.this;
        }

        public Builder setTitle(String title){
            this.title = title;
            return Builder.this;
        }

        public Dialog build(){
            if (title.isEmpty()){
                throw new IllegalArgumentException("title should not empty");
            }
            return new Dialog(this);
        }
    }

}

 Dialog dialog = new Dialog.Builder()
                .setTitle("標(biāo)題")
                .setWidth(100)
                .setHeight(100)
                .build();

原型模式
如果創(chuàng)建對象成本比較高栅隐，可以直接通過拷貝對象來獲取新對象塔嬉，拷貝對象有深拷貝和淺拷貝兩種，clone方法是淺拷貝租悄，只拷貝了索引和基本數(shù)據(jù)類型谨究，沒有拷貝對象，深拷貝是拷貝索引和引用
實(shí)現(xiàn)深拷貝的兩種方式
- 序列化對象
- 遞歸拷貝對象對象引用對象
  淺拷貝適用于不可變的數(shù)據(jù)