Question

如果存在多次改装调用，我如何进行改造的单例，以便在类中不会重复代码，从而摆脱不必要的代码。

Answer 1

这是一个例子，但是！虽然这可能是闪亮的，易于使用，但单身人士是邪恶的。尽可能避免使用它们。另一种方法是使用依赖注入。

反正。

public class Api {
    private static Api instance = null;
    public static final String BASE_URL = "your_base_url";

    // Keep your services here, build them in buildRetrofit method later
    private UserService userService;

    public static Api getInstance() {
        if (instance == null) {
            instance = new Api();
        }

        return instance;
    }

    // Build retrofit once when creating a single instance
    private Api() {
        // Implement a method to build your retrofit
        buildRetrofit(BASE_URL);
    }

    private void buildRetrofit() {
        Retrofit retrofit = ...

        // Build your services once
        this.userService = retrofit.create(UserService.class);
        ...
    }

    public UserService getUserService() {
        return this.userService;
    }
    ...
}

现在你把所有东西放在一个地方。使用它。

UserService userService = Api.getInstance().getUserService();

Answer 2

要实现单例类，最简单的方法是将类的构造函数设置为私有。

急切初始化：

在急切的初始化中，Singleton Class的实例是在类加载时创建的，这是创建单例类的最简单方法。

public class SingletonClass {

private static volatile SingletonClass sSoleInstance = new SingletonClass();

    //private constructor.
    private SingletonClass(){}

    public static SingletonClass getInstance() {
        return sSoleInstance;
    }
}

延迟初始化：

此方法将检查是否已创建该类的任何实例？如果是，那么我们的方法（getInstance（））将返回该旧实例，如果没有，则它在JVM中创建单例类的新实例并返回该实例。这种方法称为惰性初始化。

public class SingletonClass {

    private static SingletonClass sSoleInstance;

    private SingletonClass(){}  //private constructor.

    public static SingletonClass getInstance(){
        if (sSoleInstance == null){ //if there is no instance available... create new one
            sSoleInstance = new SingletonClass();
        }

        return sSoleInstance;
   }
}

还有更多的东西，比如 Java Reflection API，Thread Safe＆amp;序列化安全 Singleton。

请查看此参考，以获取更多详细信息并深入了解单例对象创建。

https://medium.com/@kevalpatel2106/digesting-singleton-design-pattern-in-java-5d434f4f322#.6gzisae2u

Answer 3

subsets(2)

Answer 4

public class Singleton  {

    private static Singleton INSTANCE = null;

    // other instance variables can be here

    private Singleton() {};

    public static Singleton getInstance() {
        if (INSTANCE == null) {
            INSTANCE = new Singleton();
        }
        return(INSTANCE);
    }

    // other instance methods can follow 
}



import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class RetrofitClient {

    private static Retrofit retrofit = null;

    public static Retrofit getClient(String baseUrl) {
        if (retrofit==null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(baseUrl)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }
}




@Module
public class NetworkModule {

    @Provides
    @Singleton
    public Gson gson() {
        GsonBuilder gsonBuilder = new GsonBuilder();
        return gsonBuilder.create();
    }

    @Provides
    @Singleton
    public HttpLoggingInterceptor loggingInterceptor() {
        HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor(
                message -> Timber.i(message));
        interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        return interceptor;
    }

    @Provides
    @Singleton
    public Cache cache(File cacheFile) {
        return new Cache(cacheFile, 10 * 1000 * 1000); //10MB Cache
    }

    @Provides
    @Singleton
    public File cacheFile(@ApplicationContext Context context) {
        return new File(context.getCacheDir(), "okhttp_cache");
    }

    @Provides
    @Singleton
    public OkHttpClient okHttpClient(HttpLoggingInterceptor loggingInterceptor, Cache cache) {
        return new OkHttpClient.Builder()
                .addInterceptor(loggingInterceptor)
                .cache(cache)
                .build();
    }

    @Provides
    @Singleton
    public Retrofit retrofit(OkHttpClient okHttpClient, Gson gson) {
        return new Retrofit.Builder()
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create(gson))
                .client(okHttpClient)
                .baseUrl("you/base/url")
                .build();
    }
}

Answer 5

我在 kotlin 中尝试过：

/:url([a-z/]*[A-Z]+[a-z/]*)/

然后：

var service：ServicesInterface？= RetrofitClient.getRetrofitObject（）?. create（ServicesInterface :: class.java）

如何为改造2制作单身？

5 个答案: