Java 和 Kotlin 单例模式写法对比

目录

1、饿汉模式

Java 写法：

Kotlin 写法：

Kotlin 这段代码反编译&简化后如下：

2、懒汉模式，静态同步方法

Java 写法：

Kotlin 写法：

Kotlin 这段代码反编译&简化后如下：

3、懒汉模式，双重检查 + 同步代码块

Java 写法：

Kotlin 写法：

Kotlin 这段代码反编译&简化后如下：

4、枚举方式

Java 写法：

Kotlin 写法：

5、静态内部类 + 静态代码块

Java 写法：

Kotlin 写法之一：

Kotlin 这段代码反编译&简化后 如下：

6、其他写法

Java 的一种写法：

Kotlin 的一种写法：

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1、饿汉模式

Java 写法：

public class SingletonDemo1 {private static SingletonDemo1 INSTANCE = new SingletonDemo1();private SingletonDemo1() {}public static SingletonDemo1 getInstance() {return INSTANCE;}}

Kotlin 写法：

object SingletonDemo1 {}

Kotlin 这段代码反编译&简化后如下：

public final class SingletonDemo1 {@NotNullpublic static final SingletonDemo1 INSTANCE = new SingletonDemo1();private SingletonDemo1() {}
}

2、懒汉模式，静态同步方法

Java 写法：

public class SingletonDemo2 {private volatile static SingletonDemo2 INSTANCE;private SingletonDemo2() {}public synchronized static SingletonDemo2 getInstance() {if (INSTANCE == null) {INSTANCE = new SingletonDemo2();}return INSTANCE;}}

Kotlin 写法：

class SingletonDemo2 private constructor() {companion object {private var INSTANCE: SingletonDemo2? = nullget() {if (field == null) {field = SingletonDemo2()}return field}@Synchronizedfun get(): SingletonDemo2 {return INSTANCE!!}}}

Kotlin 这段代码反编译&简化后如下：

public final class SingletonDemo2 {@NotNullpublic static final Companion Companion = new Companion();private static SingletonDemo2 INSTANCE;private SingletonDemo2() {}public static final class Companion {private Companion() {}@NotNullpublic final synchronized SingletonDemo2 get() {if (SingletonDemo2.INSTANCE == null) {SingletonDemo2.INSTANCE = new SingletonDemo2();}return SingletonDemo2.INSTANCE;}}public static void main(String[] args) {//调用方式SingletonDemo2 sd = SingletonDemo2.Companion.get();}
}

3、懒汉模式，双重检查 + 同步代码块

Java 写法：

public class SingletonDemo3 {private volatile static SingletonDemo3 INSTANCE;private SingletonDemo3() {}public static SingletonDemo3 getInstance() {if (INSTANCE == null) {synchronized (SingletonDemo3.class) {if (INSTANCE == null) {INSTANCE = new SingletonDemo3();}}}return INSTANCE;}}

Kotlin 写法：

这段代码涉及到高阶函数和属性委托。

Lazy 内部实现类中包含了双重判断和同步锁代码块。

class SingletonDemo3 private constructor() {companion object {val INSTANCE: SingletonDemo3 by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) {SingletonDemo3()}}}

Kotlin 这段代码反编译&简化后如下：

public final class SingletonDemo2 {@NotNullpublic static final SingletonDemo2.Companion Companion = new SingletonDemo2.Companion();@NotNullprivate static final Lazy INSTANCE$delegate;private SingletonDemo2() {}static {INSTANCE$delegate = LazyKt.lazy(LazyThreadSafetyMode.SYNCHRONIZED, (Function0)null.INSTANCE);}public static final class Companion {private Companion() {}@NotNullpublic final SingletonDemo2 getINSTANCE() {Lazy var1 = SingletonDemo2.INSTANCE$delegate;Object var2 = null;return (SingletonDemo2)var1.getValue();}}
}

4、枚举方式

Java 写法：

public enum SingletonDemo4 {INSTANCE;public void otherMethod() {}}

Kotlin 写法：

enum class SingletonDemo4 {INSTANCE;fun otherMethod() {}
}

枚举就不反编译了，没什么区别。

5、静态内部类 + 静态代码块

Java 写法：

public class SingletonDemo5 {private static class SingletonHolder {private static final SingletonDemo5 INSTANCE = new SingletonDemo5();}private SingletonDemo5() {}public static final SingletonDemo5 getInstance() {return SingletonHolder.INSTANCE;}}

Kotlin 写法之一：

class SingletonDemo5 private constructor() {companion object {val INSTANCE = SingletonHolder.holder}private object SingletonHolder {val holder = SingletonDemo5()}}

Kotlin 这段代码反编译&简化后 如下：

public final class SingletonDemo100 {@NotNullpublic static final SingletonDemo100.Companion Companion = new SingletonDemo100.Companion();@NotNullprivate static final SingletonDemo100 INSTANCE;private SingletonDemo100() {}static {INSTANCE = SingletonDemo100.SingletonHolder.INSTANCE.getHolder();}public static final class Companion {private Companion() {}@NotNullpublic final SingletonDemo100 getINSTANCE() {return SingletonDemo100.INSTANCE;}}private static final class SingletonHolder {@NotNullpublic static final SingletonDemo100.SingletonHolder INSTANCE = new SingletonDemo100.SingletonHolder();@NotNullprivate static final SingletonDemo100 holder = new SingletonDemo100();@NotNullpublic final SingletonDemo100 getHolder() {return holder;}}
}

6、其他写法

Java 的一种写法：

通过静态代码块方式，借助虚拟机在类加载时创建对象。

public class SingletonDemo6 {private volatile static SingletonDemo6 INSTANCE;static {INSTANCE = new SingletonDemo6();}private SingletonDemo6() {}public static SingletonDemo6 getInstance() {return INSTANCE;}}

Kotlin 的一种写法：

网上看别人写的，有创意，但是也很奇怪，无法完整反编译。

class SingletonDemo10 private constructor(private val property: Int) {companion object {@Volatileprivate var INSTANCE: SingletonDemo10? = nullfun getInstance(property: Int): SingletonDemo10 {return INSTANCE ?: synchronized(this) {INSTANCE ?: SingletonDemo10(property).also { INSTANCE = it }}}}}