廢話不多說，直接上程式碼，記錄一下，方便以後使用

class ImageClassifyUtil private constructor(){

    /**
     * 餓漢
     */
    companion object {
        val instance = ImageClassifyUtil()
    }

    /**
     * 懶漢
     */
    companion object {
        private var instance: ImageClassifyUtil? = null

            get() {
                if (field == null) {
                    field = ImageClassifyUtil()
                }
                return field
            }
        fun get(): ImageClassifyUtil {
            return instance!!
        }

    }

    /**
     * 執行緒安全的懶漢
     */
    companion object {
        private var instance: ImageClassifyUtil? = null

            get() {
                if (field == null) {
                    field = ImageClassifyUtil()
                }
                return field
            }
        @Synchronized
        fun get(): ImageClassifyUtil {
            return instance!!
        }

    }


    /**
     * 雙重校驗
     */
    companion object {
        val instance: ImageClassifyUtil by lazy(mode = LazyThreadSafetyMode.SYNCHRONIZED) {
            ImageClassifyUtil()
        }
    }

    /**
     * 靜態內部類
     */
    companion object {
        val instance = ImageClassifyHolder.holder
    }

    private object ImageClassifyHolder {
        val holder = ImageClassifyUtil()
    }
    
}
 

ps:歷史給人的唯一教訓，就是人們從未在歷史中吸取過任何教訓

ps:秦人不暇自哀，而後人哀之；後人哀之而不鑑之，亦使後人而復哀後人也”基本同義。