目录
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 {
@NotNull
public 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? = null
get() {
if (field == null) {
field = SingletonDemo2()
}
return field
}
@Synchronized
fun get(): SingletonDemo2 {
return INSTANCE!!
}
}
}Kotlin 这段代码反编译&简化后如下：
public final class SingletonDemo2 {
@NotNull
public static final Companion Companion = new Companion();
private static SingletonDemo2 INSTANCE;
private SingletonDemo2() {
}
public static final class Companion {
private Companion() {
}
@NotNull
public 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 {
@NotNull
public static final SingletonDemo2.Companion Companion = new SingletonDemo2.Companion();
@NotNull
private static final Lazy INSTANCE$delegate;
private SingletonDemo2() {
}
static {
INSTANCE$delegate = LazyKt.lazy(LazyThreadSafetyMode.SYNCHRONIZED, (Function0)null.INSTANCE);
}
public static final class Companion {
private Companion() {
}
@NotNull
public 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 {
@NotNull
public static final SingletonDemo100.Companion Companion = new SingletonDemo100.Companion();
@NotNull
private static final SingletonDemo100 INSTANCE;
private SingletonDemo100() {
}
static {
INSTANCE = SingletonDemo100.SingletonHolder.INSTANCE.getHolder();
}
public static final class Companion {
private Companion() {
}
@NotNull
public final SingletonDemo100 getINSTANCE() {
return SingletonDemo100.INSTANCE;
}
}
private static final class SingletonHolder {
@NotNull
public static final SingletonDemo100.SingletonHolder INSTANCE = new SingletonDemo100.SingletonHolder();
@NotNull
private static final SingletonDemo100 holder = new SingletonDemo100();
@NotNull
public 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 {
@Volatile
private var INSTANCE: SingletonDemo10? = null
fun getInstance(property: Int): SingletonDemo10 {
return INSTANCE ?: synchronized(this) {
INSTANCE ?: SingletonDemo10(property).also { INSTANCE = it }
}
}
}
}