對(duì)象聲明就是單例了杨凑。object DataProviderManager就可以理解為創(chuàng)建了類DataProviderManager并且實(shí)現(xiàn)了單例模式。
測(cè)試代碼

class test {
    object DataProviderManager {
        fun registerDataProvider(provider: String) {
            // ……
        }

        val allDataProviders: Collection<String>
            get() = listOf("a")

    }

    fun test() {
        DataProviderManager.registerDataProvider("")
    }
}

class MyClass {
    companion object {
          var a: String = ""
        
        fun create(): MyClass = MyClass()
    }

    fun test() {
        MyClass.create()
    }
}

class MyClass1 {

    companion object {

         @JvmStatic
        var a: String = ""

        @JvmStatic
        fun create(): MyClass1 = MyClass1()
    }

    fun test() {
        MyClass1.create()
    }
}

查看kotlin最終生成的java代碼
Tools->Kotlin -> Decompile Kotlin to Java
然后點(diǎn)擊上面的Decompile按鈕忌锯，會(huì)得到轉(zhuǎn)化后的java文件礼殊，如下

// MyClass.java

import kotlin.Metadata;
import kotlin.jvm.internal.DefaultConstructorMarker;
import org.jetbrains.annotations.NotNull;

public final class MyClass {
   public static final MyClass.Companion Companion = new MyClass.Companion((DefaultConstructorMarker)null);

   public final void test() {
      Companion.create();
   }

   public static final class Companion {
     @NotNull
      public final String getA() {
         return MyClass.a;
      }

      public final void setA(@NotNull String var1) {
         Intrinsics.checkParameterIsNotNull(var1, "<set-?>");
         MyClass.a = var1;
      }

      @NotNull
      public final MyClass create() {
         return new MyClass();
      }

      private Companion() {
      }

      // $FF: synthetic method
      public Companion(DefaultConstructorMarker $constructor_marker) {
         this();
      }
   }
}
// test.java

import java.util.Collection;
import kotlin.Metadata;
import kotlin.collections.CollectionsKt;
import kotlin.jvm.internal.Intrinsics;
import org.jetbrains.annotations.NotNull;

public final class test {
   public final void test() {
      test.DataProviderManager.INSTANCE.registerDataProvider("");
   }

   public static final class DataProviderManager {
      public static final test.DataProviderManager INSTANCE;

      public final void registerDataProvider(@NotNull String provider) {
         Intrinsics.checkParameterIsNotNull(provider, "provider");
      }

      @NotNull
      public final Collection getAllDataProviders() {
         return (Collection)CollectionsKt.listOf("a");
      }

      private DataProviderManager() {
         INSTANCE = (test.DataProviderManager)this;
      }

      static {
         new test.DataProviderManager();
      }
   }
}
// MyClass1.java

import kotlin.Metadata;
import kotlin.jvm.JvmStatic;
import kotlin.jvm.internal.DefaultConstructorMarker;
import org.jetbrains.annotations.NotNull;

public final class MyClass1 {
  @NotNull
   private static String a = "";
   public static final MyClass1.Companion Companion = new MyClass1.Companion((DefaultConstructorMarker)null);

   public final void test() {
      Companion.create();
   }

@NotNull
   public static final String getA() {
      return Companion.getA();
   }

   public static final void setA(@NotNull String var0) {
      Intrinsics.checkParameterIsNotNull(var0, "<set-?>");
      Companion.setA(var0);
   }

   @JvmStatic
   @NotNull
   public static final MyClass1 create() {
      return Companion.create();
   }

   public static final class Companion {
      @JvmStatic
      @NotNull
      public final MyClass1 create() {
         return new MyClass1();
      }

      private Companion() {
      }

      // $FF: synthetic method
      public Companion(DefaultConstructorMarker $constructor_marker) {
         this();
      }
   }
}

1. 看生成的test.java泌参，里面的DataProviderManager就是個(gè)單例盖溺。object DataProviderManager就可以理解為創(chuàng)建了類DataProviderManager并且實(shí)現(xiàn)了單例模式。
   調(diào)用DataProviderManager.registerDataProvider("")對(duì)應(yīng)的java代碼就是DataProviderManager.INSTANCE.registerDataProvider("")

常見(jiàn)調(diào)用單例類方法代碼DataProviderManager.getInstance().registerDataProvider("")，只是獲得instance方式不一樣而已

2. Companion object就不是單例哮内，就把它當(dāng)做靜態(tài)變量就好了。加了@JvmStatic之后MyClass1中多了private static String a = "";和public static final MyClass1 create() {

在 JVM 平臺(tái)，如果使用 @JvmStatic 注解，你可以將伴生對(duì)象的成員生成為真正的靜態(tài)方法和字段。

有同學(xué)會(huì)問(wèn)驳棱，我怎么實(shí)現(xiàn)一個(gè)單例類給其他類用呢？

就像上面說(shuō)的一樣，object className就相當(dāng)于定義了一個(gè)實(shí)現(xiàn)單例模式的類。所以我們?cè)谀硞€(gè)kt文件中寫(xiě)如下代碼

object UserHelper{
    var username:String = ""
}

class LoginActivity{

    fun doLogin(name:String){
        UserHelper.username = name
    }
}

我們創(chuàng)建了一個(gè)UserHelper單例類拆祈，用來(lái)保存登錄用戶的信息老玛；LoginActivity里面用戶登錄逻炊，讓返回的name賦值給UserHelper互亮、
Decompile kotlin to java

public final class LoginActivity {
   public final void doLogin(@NotNull String name) {
      Intrinsics.checkParameterIsNotNull(name, "name");
      UserHelper.INSTANCE.setUsername(name);
   }
}
// UserHelper.java
package com.xstudy.assistteacher.module.inclass;

import kotlin.Metadata;
import kotlin.jvm.internal.Intrinsics;
import org.jetbrains.annotations.NotNull;

public final class UserHelper {
   @NotNull
   private static String username;
   public static final UserHelper INSTANCE;

   @NotNull
   public final String getUsername() {
      return username;
   }

   public final void setUsername(@NotNull String var1) {
      Intrinsics.checkParameterIsNotNull(var1, "<set-?>");
      username = var1;
   }

   private UserHelper() {
      INSTANCE = (UserHelper)this;
      username = "";
   }

   static {
      new UserHelper();
   }
}