一、饿汉式的实现

Kotlin版本

object SingletonDemoKt/***  背后的逻辑代码：public final class SingletonDemoKt {public static final SingletonDemoKt INSTANCE;private SingletonDemoKt() {}static {SingletonDemoKt var0 = new SingletonDemoKt();INSTANCE = var0;}}*/

Java版本

public class SingletonDemo {private static SingletonDemo mInstance = new SingletonDemo();private SingletonDemo() {}public static SingletonDemo getInstance() {return mInstance;}
}

二、懒汉式的实现

Kotlin版本

class SingletonDemo2Kt {companion object {private var mInstance : SingletonDemo2Kt? = nullget() {if (field == null) {field = SingletonDemo2Kt()}return field}fun getInstance() = mInstance!!}fun show() {println("SingletonDemo2Kt show")}
}fun main() {SingletonDemo2Kt.getInstance().show()
}/*** 背后逻辑代码：public final class SingletonDemo2Kt {private static SingletonDemo2Kt mInstance;public static final SingletonDemo2Kt.Companion Companion = new SingletonDemo2Kt.Companion((DefaultConstructorMarker)null);public final void show() {String var1 = "SingletonDemo2Kt show";boolean var2 = false;System.out.println(var1);}...public static final class Companion {private final SingletonDemo2Kt getMInstance() {if (SingletonDemo2Kt.mInstance == null) {SingletonDemo2Kt.mInstance = new SingletonDemo2Kt();}return SingletonDemo2Kt.mInstance;}private final void setMInstance(SingletonDemo2Kt var1) {SingletonDemo2Kt.mInstance = var1;}@NotNullpublic final SingletonDemo2Kt getInstance() {SingletonDemo2Kt var10000 = ((SingletonDemo2Kt.Companion)this).getMInstance();if (var10000 == null) {Intrinsics.throwNpe();}return var10000;}private Companion() {}// $FF: synthetic methodpublic Companion(DefaultConstructorMarker $constructor_marker) {this();}}}*/

Java版本

public class SingletonDemo2 {private static SingletonDemo2 mInstance;private SingletonDemo2() {}public static SingletonDemo2 getInstance() {if (mInstance == null) {mInstance = new SingletonDemo2();}return mInstance;}public static void show() {System.out.println("SingletonDemo2 show");}public static void main(String[] args) {SingletonDemo2.getInstance().show();}
}

三、安全 懒汉式的实现

Kotlin实现

class SingletonDemo3Kt {companion object {private var mInstance : SingletonDemo3Kt? = nullget() {if (field == null) {field = SingletonDemo3Kt()}return field}@Synchronizedfun getInstance() = mInstance!!}fun show() {println("SingletonDemo3Kt show")}
}fun main() {SingletonDemo3Kt.getInstance().show()
}/*** 背后逻辑代码：public final class SingletonDemo2Kt {private static SingletonDemo2Kt mInstance;public static final SingletonDemo2Kt.Companion Companion = new SingletonDemo2Kt.Companion((DefaultConstructorMarker)null);public final void show() {String var1 = "SingletonDemo2Kt show";boolean var2 = false;System.out.println(var1);}...public static final class Companion {private final SingletonDemo2Kt getMInstance() {if (SingletonDemo2Kt.mInstance == null) {SingletonDemo2Kt.mInstance = new SingletonDemo2Kt();}return SingletonDemo2Kt.mInstance;}private final void setMInstance(SingletonDemo2Kt var1) {SingletonDemo2Kt.mInstance = var1;}@NotNullpublic final SingletonDemo2Kt getInstance() {SingletonDemo2Kt var10000 = ((SingletonDemo2Kt.Companion)this).getMInstance();if (var10000 == null) {Intrinsics.throwNpe();}return var10000;}private Companion() {}// $FF: synthetic methodpublic Companion(DefaultConstructorMarker $constructor_marker) {this();}}}*/

Java版本

public class SingletonDemo3 {private static SingletonDemo3 mInstance;private SingletonDemo3() {}public static synchronized SingletonDemo3 getInstance() {if (mInstance == null) {mInstance = new SingletonDemo3();}return mInstance;}public static void show() {System.out.println("SingletonDemo3 show");}public static void main(String[] args) {SingletonDemo3.getInstance().show();}
}

四、双重校验DCL 的实现

Kotlin实现

class SingletonDemo4Kt private constructor() {companion object {val mInstance : SingletonDemo4Kt by lazy (mode = LazyThreadSafetyMode.SYNCHRONIZED) { SingletonDemo4Kt() }}fun show() {println("SingletonDemo4Kt show")}
}
fun main() {SingletonDemo4Kt.mInstance.show()
}

Java实现

public class SingletonDemo4 {private volatile static SingletonDemo4 mInstance;private SingletonDemo4() {}public static SingletonDemo4 getInstance() {if (mInstance == null) {synchronized (SingletonDemo4.class) {if (mInstance == null) {mInstance = new SingletonDemo4();}}}return mInstance;}public void show() {System.out.println("show");}public static void main(String[] args) {SingletonDemo4.getInstance().show();}
}