读取assets中的文本内容

resources.assets.open("test.txt").let {
    it.buffered().reader().use { reader ->
        Log.e("test", "${reader.readText()}")
    }
}

统计字符出现的次数("io.reactivex:rxjava:1.2.1")

/**
 * filter中过滤掉空字符
 * groupBy 分组
 * o.count 进行统计，得到的是一个observable
 */
//    Observable.from(txt.toCharArray().asIterable()).filter { !it.isWhitespace() }.groupBy { it }.map(::println)
Observable.from(txt.toCharArray().asIterable()).filter { !it.isWhitespace() }.groupBy { it }.map { o ->
    o.count().subscribe {
        println("key = ${o.key} , count = $it")
    }
}.subscribe()

retrofit发送get请求

interface GithubService {
    @GET("/repos/enbandari/Kotlin-Tutorials/stargazers")
    fun getUserInfos(): Call<List<User>>
}

// object单例类
object ServiceManager {
    val apiService: GithubService by lazy {
        Retrofit.Builder().baseUrl("https://api.github.com")
            .addConverterFactory(GsonConverterFactory.create()).build().create(GithubService::class.java)
    }
}

data class User(val login: String, val id: Long, val avatar_url: String)

单例类的5种实现方式对比

java

第一种方式

public class LazyNotThreadSafe {
    private static LazyNotThreadSafe INSTANCE;

    private LazyNotThreadSafe() {
    }

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

第二种方式

public class LazyThreadSafeDoubleCheck {
    private static LazyThreadSafeDoubleCheck INSTANCE;

    private LazyThreadSafeDoubleCheck() {
    }

    public static LazyThreadSafeDoubleCheck getInstance() {
        if (INSTANCE == null) {
            synchronized (LazyThreadSafeDoubleCheck.class) {
                if (INSTANCE == null) {
                    //初始化时分为实例化和赋值两步, 尽管我们把这一步写成下面的语句,
                    // 但Java虚拟机并不保证其他线程『眼中』这两步的顺序究竟是怎么样的
                    INSTANCE = new LazyThreadSafeDoubleCheck();
                }
            }
        }
        return INSTANCE;
    }
}

第三种方式

public class LazyThreadSafeStaticInnerClass {
    private static class Holder {
        private static LazyThreadSafeStaticInnerClass INSTANCE = new LazyThreadSafeStaticInnerClass();
    }

    private LazyThreadSafeStaticInnerClass() {
    }

    public static LazyThreadSafeStaticInnerClass getInstance() {
        return Holder.INSTANCE;
    }
}

第四种方式

public class LazyThreadSafeSynchronized {
    private static LazyThreadSafeSynchronized INSTANCE;

    private LazyThreadSafeSynchronized() {
    }

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

第五种方式

public class PlainOldSingleton {
    private static PlainOldSingleton INSTANCE = new PlainOldSingleton();

    private PlainOldSingleton() {
    }

    public static PlainOldSingleton getInstance() {
        return INSTANCE;
    }
}

kotlin

第一种方式

class LazyNotThreadSafe private constructor(){
    companion object {
        val instance by lazy {
            LazyNotThreadSafe()
        }

        // 下面是另一种等价的写法, 获取单例使用 get 方法
        private var instance2: LazyNotThreadSafe? = null

        fun get(): LazyNotThreadSafe {
            if (instance2 == null)
                instance2 = LazyNotThreadSafe()
            return instance2!!
        }
    }
}

第二种方式

class LazyThreadSafeDoubleCheck private constructor() {
    companion object {
        val instance by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) {
            LazyThreadSafeDoubleCheck()
        }

        private @Volatile
        var instance2: LazyThreadSafeDoubleCheck? = null

        fun get(): LazyThreadSafeDoubleCheck {
            if (instance2 == null) {
                synchronized(this) {
                    if (instance2 == null) {
                        instance2 = LazyThreadSafeDoubleCheck()
                    }
                }
            }
            return instance2!!
        }
    }
}

第三种方式

class LazyThreadSafeStaticInnerClass private constructor() {
    companion object {
        fun getInstance() = Holder.instance
    }

    private object Holder {
        val instance= LazyThreadSafeStaticInnerClass()
    }
}

第四种方式

class LazyThreadSafeSynchronized private constructor() {
    companion object {
        private var instance: LazyThreadSafeSynchronized? = null

        @Synchronized
        fun get(): LazyThreadSafeSynchronized {
            if (instance == null)
                instance = LazyThreadSafeSynchronized()
            return instance!!
        }
    }
}

第五种方式

/**
 * 定义的类本身就是单例类
 */
object PlainOldSingleton

动态代理之解决reified不足的问题

{
  "code": 0,
  "message": "ok",
  "content": {
    "id": 1,
    "name": "Unknown",
    "songs": [
      {
        "id": 0,
        "name": "Rada"
      },
      {
        "id": 1,
        "name": "Olympic Dream"
      },
      {
        "id": 2,
        "name": "The Escapist"
      }
    ]
  }
}

Gson的扩展方法

// 通常情况下使用inline+reified解决泛型不被擦
inline fun <reified T : Any> Gson.fromJson(json: String): T {
    return fromJson(json, T::class.java)
}

通过动态代理获取到Singer类型

interface Api {
    fun getSingerFromJson(json: String): BaseResult<Singer>
}

object ApiFactory {
    val api: Api by lazy {
        Proxy.newProxyInstance(
            ApiFactory.javaClass.classLoader,
            arrayOf(Api::class.java)
        ) { proxy, method, args ->
            // 获取方法的返回值类型
            val responseType = method.genericReturnType
            val adapter = Gson().getAdapter(TypeToken.get(responseType))
            adapter.fromJson(args[0].toString())
        } as Api
    }
}

代码示例：

val text = File("result_singer.json").readText()
val result: BaseResult<Singer> = gson.fromJson(text)

BaseResult(code=0, message=ok, content={id=1.0, name=Unknown, songs=[{id=0.0, name=Rada}, {id=1.0, name=Olympic Dream}, {id=2.0, name=The Escapist}]})

代码示例

val result2: BaseResult<Singer> = ApiFactory.api.getSingerFromJson(text)
println(result2)

BaseResult(code=0, message=ok, content=Singer(id=1, name=Unknown, songs=[Song(id=0, name=Rada), Song(id=1, name=Olympic Dream), Song(id=2, name=The Escapist)]))

使用高阶函数替换java中的回调接口

java代码

public class TaskExecutor {
    private OnCompletionListener onCompletionListener;

    public interface OnCompletionListener {
        void onDone(long time);
    }

    public void setListener(OnCompletionListener listener) {
        this.onCompletionListener = listener;
    }

    public void execute() {
        Executors.newSingleThreadExecutor().execute(() -> {
            for (int i = 0; i < 5; i++) {
                System.out.println("time num " + i);
            }
            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            if (onCompletionListener != null) {
                onCompletionListener.onDone(new Date().getTime());
            }
        });
    }
}

调用

val taskExecutor = TaskExecutor()
taskExecutor.setListener {
    object : TaskExecutor.OnCompletionListener {
        override fun onDone(time: Long) {
            println("time = $time")
        }
    }
}
//    taskExecutor.execute()
println()

taskExecutor.setListener {
    TaskExecutor.OnCompletionListener { time -> println("time = $time") }
}
//    taskExecutor.execute()
//    println()

kotlin代码

class KTTaskExecutor {
    // 定义lambda表达式
    private var listener: (Long) -> Unit = {}

    // 设置接口
    fun setListener(e: (Long) -> Unit) {
        this.listener = e
    }

    fun exec(e: (Long) -> Unit) {
        this.listener = e
        Executors.newSingleThreadExecutor().execute {
            for (i in 1..5) {
                println("index at $i")
            }
            Thread.sleep(500)
            e(Date().time) // 调用函数并传入数据
        }
    }
}

未改造前

class Request(val url: String) {
    public fun run(callback: Callback) {
        async {
            val readText = URL(url).readText()
            println("${javaClass.simpleName} , $readText")
            uiThread {
                println("${javaClass.simpleName} , $readText")
                callback.done(readText)
            }
        }
    }

    public interface Callback {
        fun done(data: String)
    }
}

改造后

class AdvRequest(val url: String) {
    // 匿名接口，需要传入一个数据
    var listener: (String) -> Unit = {}
        private set

    fun run(e: (String) -> Unit) {
        async {
            val readText = URL(url).readText()
            println("${javaClass.simpleName} , $readText")
            uiThread {
                println("${javaClass.simpleName} , $readText")
                e(readText)
            }
        }
    }
}

调用

KTTaskExecutor().exec { time ->
    println("kttime = $time")
}


btn_exec_net_req.onClick {
    rl_loading2.visibility = View.VISIBLE
    Request(AppConst.API_REQ_STARTS).run(object : Request.Callback {
        override fun done(data: String) {
            tv_result.text = data
            rl_loading2.visibility = View.GONE
        }
    })
}

btn_exec_net_req2.onClick {
    rl_loading2.visibility = View.VISIBLE
    AdvRequest(AppConst.API_REQ_STARTS).run { e ->
        tv_result.text = e
        rl_loading2.visibility = View.GONE
    }
}