用Kotlin-koans學Kotlin【四】 iii_conventions

HankeXu發表於2017-10-17
Kotlin

本節練習Kotlin中各種介面的使用

25. n25Comparison

為Mydate類實現Comparable介面，式其可以通過我們在Comparable介面中定義的規則直接比較

data class MyDate(val year: Int, val month: Int, val dayOfMonth: Int) : Comparable<MyDate> {
    override fun compareTo(other: MyDate): Int = when {
        year != other.year -> year - other.year
        month != other.month -> month - other.month
        else -> dayOfMonth - other.dayOfMonth
    }
}複製程式碼

26. n26InRange

為DateRange類實現方法，判斷某個Mydate物件是否在DateRange的範圍中

class DateRange(val start: MyDate, val endInclusive: MyDate){
    operator fun contains(item:MyDate):Boolean = start<=item&&item<=endInclusive
}複製程式碼

也可以

class DateRange(override val start: MyDate, override val endInclusive: MyDate) : ClosedRange<MyDate> {
    override fun contains(item: MyDate): Boolean = start <= item && item <= endInclusive
}複製程式碼

引數前新增了override是因為CloseRange介面中也定義了這兩個屬性，所以我們實現該介面也就複寫了這兩個引數

27. n27RangeTo

實現rangeTo介面，該介面的功能是返回一個從當前物件到目標物件的一個集合

operator fun MyDate.rangeTo(other: MyDate): DateRange =DateRange(this,other)複製程式碼

28. n28ForLoop

為DateRange實現Iterable介面
可以專門建立一個類，也可以用物件表示式

class DateRange(override val start: MyDate, override val endInclusive: MyDate) : ClosedRange<MyDate>, Iterable<MyDate> {
    override fun iterator(): Iterator<MyDate> = object : Iterator<MyDate> {
        var current: MyDate = start
        override fun next(): MyDate {
            val result = current
            current = current.nextDay()
            return result
        }
        override fun hasNext(): Boolean = current <= endInclusive

    }

    override fun contains(item: MyDate): Boolean = start <= item && item <= endInclusive
}複製程式碼
class DateRange(override val start: MyDate, override val endInclusive: MyDate) : ClosedRange<MyDate>, Iterable<MyDate> {
    override fun iterator(): Iterator<MyDate> =DateIterator(this)
    override fun contains(item: MyDate): Boolean = start <= item && item <= endInclusive
}

class DateIterator(val dateRange:DateRange) : Iterator<MyDate> {
    var current: MyDate = dateRange.start
    override fun next(): MyDate {
        val result = current
        current = current.nextDay()
        return result
    }
    override fun hasNext(): Boolean = current <= dateRange.endInclusive
}複製程式碼

29. n29OperatorsOverloading

過載操作符，僅+

operator fun MyDate.plus(timeInterval: TimeInterval) = addTimeIntervals(timeInterval,1)複製程式碼

為TimeInterval過載*，呼叫時一定要TimeInterval在前

class RepeatedTimeInterval(val ti: TimeInterval, val n: Int=1)
operator fun TimeInterval.times(number:Int) = RepeatedTimeInterval(this,number)
operator fun MyDate.plus(timeInterval: RepeatedTimeInterval) = addTimeIntervals(timeInterval.ti,timeInterval.n)複製程式碼

30. n30DestructuringDeclarations

用解構宣告解構物件

class MyDate(val year: Int, val month: Int, val dayOfMonth: Int) {
    operator fun component1(): Int =year
    operator fun component2(): Int =month
    operator fun component3(): Int =dayOfMonth
}複製程式碼

31. n31Invoke

統計呼叫次數，這裡使用了閉包

class Invokable{
    var numberOfInvocations: Int = 0
        private set
    operator fun invoke():Invokable  {
        numberOfInvocations++
        return this
    }
}複製程式碼

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