kotlin constructor init companion object 与初始化by lazy

冷不防 2023-10-12 13:17 51阅读 0赞

## kotlin constructor init companion object 与初始化by lazy ##

##  ##

class MyDemo(private var v: Int) {
        init {
            println("init $v")
        }
    
        constructor(m: Int, n: Int) : this(m) {
            println("constructor $m $n")
        }
    
        //只初始化一次
        companion object {
            private var TAG = "fly"
    
            init {
                println("companion object $TAG")
            }
    
            val instance: MyDemo by lazy {
                MyDemo(0)
            }
        }
    
        fun foo() {
            println("foo $v")
        }
    }
    
    fun main(args: Array<String>) {
        MyDemo(1)
        MyDemo.instance.foo()
        println("---")
        MyDemo(2, 3)
        MyDemo.instance.foo()
    }

> companion object fly  
> init 1  
> init 0  
> foo 0  
> \---  
> init 2  
> constructor 2 3  
> foo 0

[kotlin用object实现单例模式，companion object与java静态\_zhangphil的博客-CSDN博客kotlin中很容易使用object实现java中的单例模式。由于kotlin中没有static修饰词，可以用companion object实现Java中的static效果。kotlin用object实现单例模式，companion object与java静态。可以看到object定义的Singleton只初始化一次。方法 - mymethod。![favicon32.ico][]https://blog.csdn.net/zhangphil/article/details/129242135][kotlin_object_companion object_java_zhangphil_-CSDN_kotlin_object_java_kotlin_static_companion object_Java_static_kotlin_object_companion object_java_object_Singleton_ - mymethod_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_129242135]

[kotlin懒加载lazy与lateinit延迟初始化\_zhangphil的博客-CSDN博客lazy 用于单例模式，当且仅当变量被第一次调用时候，才会执行。lazy()第一次调用会执行并记录结果，后续调用只返回结果。lateinit 用于变量 var， lazy 用于常量 val。耗费很重资源初始化的类。![favicon32.ico][]https://blog.csdn.net/zhangphil/article/details/129262829][kotlin_lazy_lateinit_zhangphil_-CSDN_lazy _lazy_lateinit _ var_ lazy _ val_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_129262829]

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