聊聊Kotlin 中 lateinit 和 lazy 的原理区别

 class InitTest() {
     lateinit var name: String
 ​
     public fun checkName(): Boolean = name.isNotEmpty()
 }

 AndroidRuntime: FATAL EXCEPTION: main
      Caused by: kotlin.UninitializedPropertyAccessException: lateinit property name has not been initialized
         at com.example.tiramisu_demo.kotlin.InitTest.getName(InitTest.kt:4)
         at com.example.tiramisu_demo.kotlin.InitTest.checkName(InitTest.kt:10)
         at com.example.tiramisu_demo.MainActivity.testInit(MainActivity.kt:365)
         at com.example.tiramisu_demo.MainActivity.onButtonClick(MainActivity.kt:371)
         ...

 class InitTest() {
     lateinit var name: String
 ​
     fun checkName(): Boolean {
         return if (::name.isInitialized) {
             name.isNotEmpty()
         } else {
             false
         }
     }
 }

 Init: testInit():false

 class InitTest() {
     lateinit var name: String
 ​
     fun injectName(name: String) {
         this.name = name
     }
 ​
     fun checkName(): Boolean {
         return if (::name.isInitialized) {
             name.isNotEmpty()
         } else {
             false
         }
     }
 }

 Init: testInit():true

 public final class InitTest {
    public String name;
        
    @NotNull
    public final String getName() {
       String var10000 = this.name;
       if (var10000 == null) {
          Intrinsics.throwUninitializedPropertyAccessException("name");
       }
 ​
       return var10000;
    }
 ​
     public final boolean checkName() {
       String var10000 = this.name;
       if (var10000 == null) {
          Intrinsics.throwUninitializedPropertyAccessException("name");
       }
 ​
       CharSequence var1 = (CharSequence)var10000;
       return var1.length() > 0;
    }
 }

 public class Intrinsics {
     public static void throwUninitializedPropertyAccessException(String propertyName) {
         throwUninitializedProperty("lateinit property " + propertyName + " has not been initialized");
     }
 ​
     public static void throwUninitializedProperty(String message) {
         throw sanitizeStackTrace(new UninitializedPropertyAccessException(message));
     }
 ​
     private static <T extends Throwable> T sanitizeStackTrace(T throwable) {
         return sanitizeStackTrace(throwable, Intrinsics.class.getName());
     }
 ​
     static <T extends Throwable> T sanitizeStackTrace(T throwable, String classNameToDrop) {
         StackTraceElement[] stackTrace = throwable.getStackTrace();
         int size = stackTrace.length;
 ​
         int lastIntrinsic = -1;
         for (int i = 0; i < size; i++) {
             if (classNameToDrop.equals(stackTrace[i].getClassName())) {
                 lastIntrinsic = i;
             }
         }
 ​
         StackTraceElement[] newStackTrace = Arrays.copyOfRange(stackTrace, lastIntrinsic + 1, size);
         throwable.setStackTrace(newStackTrace);
         return throwable;
     }
 }
 ​
 public actual class UninitializedPropertyAccessException : RuntimeException {
     ...
 }

 class InitTest() {
     val name: String = "test"
 ​
     public fun checkName(): Boolean = name.isNotEmpty()
 }

 public final class InitTest {
    @NotNull
    private String name = "test";
 ​
    @NotNull
    public final String getName() {
       return this.name;
    }
 ​
    public final boolean checkName() {
       CharSequence var1 = (CharSequence)this.name;
       return var1.length() > 0;
    }
 }

 public final class InitTest {
    public String name;
    ...
    public final boolean checkName() {
       boolean var2;
       if (((InitTest)this).name != null) {
          String var10000 = this.name;
          if (var10000 == null) {
             Intrinsics.throwUninitializedPropertyAccessException("name");
          }
 ​
          CharSequence var1 = (CharSequence)var10000;
          var2 = var1.length() > 0;
       } else {
          var2 = false;
       }
 ​
       return var2;
    }
 }

 class InitTest {
     val name by lazy {
         "test"
     }
     
     public fun checkName(): Boolean = name.isNotEmpty()
 }

 Init: testInit():true

 public final class InitTest {
    @NotNull
    private final Lazy name$delegate;
 ​
    @NotNull
    public final String getName() {
       Lazy var1 = this.name$delegate;
       return (String)var1.getValue();
    }
 ​
    public final boolean checkName() {
       CharSequence var1 = (CharSequence)this.getName();
       return var1.length() > 0;
    }
 ​
    public InitTest() {
       this.name$delegate = LazyKt.lazy((Function0)null.INSTANCE);
    }
 }

 public actual fun <T> lazy(initializer: () -> T): Lazy<T> = SynchronizedLazyImpl(initializer)
 ​
 private class SynchronizedLazyImpl<out T>(initializer: () -> T, lock: Any? = null) : Lazy<T>, Serializable {
     private var initializer: (() -> T)? = initializer
     @Volatile private var _value: Any? = UNINITIALIZED_VALUE
     // final field is required to enable safe publication of constructed instance
     private val lock = lock ?: this
 ​
     override val value: T
         get() {
             val _v1 = _value
             if (_v1 !== UNINITIALIZED_VALUE) {
                 @Suppress("UNCHECKED_CAST")
                 return _v1 as T
             }
 ​
             return synchronized(lock) {
                 val _v2 = _value
                 if (_v2 !== UNINITIALIZED_VALUE) {
                     @Suppress("UNCHECKED_CAST") (_v2 as T)
                 } else {
                     val typedValue = initializer!!()
                     _value = typedValue
                     initializer = null
                     typedValue
                 }
             }
         }
 ​
     override fun isInitialized(): Boolean = _value !== UNINITIALIZED_VALUE
 ​
     override fun toString(): String = if (isInitialized()) value.toString() else "Lazy value not initialized yet."
 ​
     private fun writeReplace(): Any = InitializedLazyImpl(value)
 }

 public class Singleton {
     private static volatile Singleton singleton;
 ​
     private Singleton() {
     }
 ​
     public static Singleton getInstance() {
         if (singleton == null) {
             synchronized (Singleton.class) {
                 if (singleton == null) {
                     singleton = new Singleton();
                 }
             }
         }
         return singleton;
     }
 }

     val name by lazy(lock) {
         "test"
     }

     val name by lazy(LazyThreadSafetyMode.PUBLICATION) {
         "test"
     }

     val name by lazy(LazyThreadSafetyMode.NONE) {
         "test"
     }