目前java中的单例模式有多种写法，kotlin中的写法更多一点，本篇会总结全部的到单例模式写法。
一、懒人写法（恶汉式）
java中
public class Singleton{
public static final Singleton instance = new Singleton();
public Singleton getInstance() {
return instance;
}
}
kotlin中
最简单的写法，直接用object声明
object Singleton{}
二、基本懒加载（未实现线程同步）
注：这种方式实现了懒加载，但是不是线程安全的，可能在多个线程中创建多个不同的实例
java中
public class Singleton {
public static Singleton instance = null;
private Singleton (){}
public Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
kotlin中
class Singleton private constructor{
companion object {
val intance by lazy(LazyThreadSafetyMode.NONE) { Singleton() }
}
}
三、线程同步单例1
注：其实kotlin这种写法可以说是java直译过来的，虽说是线程安全的，但是太影响效率，主要看下面这种
java中
public class Singleton {
private static Singleton instance = null;
private Singleton (){}
public static synchronized Singleton getInstance() {
if (instance == null) {
instance = new Singleton();
}
return instance;
}
}
kotlin中
class Singleton private constructor(){
companion object {
lateinit var instance: Singleton
@Synchronized
fun get(): Singleton {
if (instance == null) {
instance = Singleton();
}
return instance!!
}
}
}
四、线程同步单例2
注：线程同步，懒加载，无同步引起的效率问题
java中双检锁单例
public class Singleton {
private static Singleton instance = null;
private Singleton (){}
public static Singleton getInstance() {
if (instance == null) {
synchronized (Singleton.class) {
if (instance == null) {
instance = new Singleton();
}
}
}
return instance;
}
}
kotlin
class Singleton private constructor(){
companion object {
val intance by lazy(LazyThreadSafetyMode.SYNCHRONIZED) { Singleton() }
}
}
五、静态内部类单例
java中
public class Singleton {
private Singleton (){}
private static class Holder {
private static Singleton instance = new Singleton();
}
public static Singleton getInstance(){
return Holder.instance;
}
}
kotlin中
class Singleton private constructor(){
companion object {
fun getInstance(): Singleton {
return Holder.instance
}
}
private object Holder {
val instance = Singleton()
}
}
最后，希望此篇博客对大家有所帮助，欢迎提出问题及建议共同探讨，如有兴趣可以关注我的博客，谢谢！
