Kotlin函数（三）

函数joinToString

函数joinToString想要打印列表的内容，需要传人四个参数：列表、分隔符、前缀和后缀
打印列表的内容：

fun <T> joinToString(collection: Collection<T>,
                     separator: String,
                     prefix: String,
                     postfix: String): String {
    val result = StringBuilder(prefix)
    for ((index, element) in collection.withIndex()) {
        if (index > 0) result.append(separator)
        result.append(element)
    }
    result.append(postfix)
    return result.toString()
}

测试：

fun printList() {
    val list = listOf(2, 4, 0)
    //不标明参数名
    println(joinToString(list, " - ", "[", "]"))
    //显示的标明参数名称
    println(joinToString(list, separator = " - ", prefix = "[", postfix = "]"))
}

定义函数的时候还可以给函数默认的参数
打印列表的内容：（带有默认的参数，可以避免java的函数重载）

fun <T> joinToString2(collection: Collection<T>,
                      separator: String = ", ",
                      prefix: String = "",
                      postfix: String = ""): String {
    val result = StringBuilder(prefix)
    for ((index, element) in collection.withIndex()) {
        if (index > 0) result.append(separator)
        result.append(element)
    }
    result.append(postfix)
    return result.toString()
}

测试：

fun printList3() {
    val list = listOf(2, 4, 0)
    println(joinToString2(list, " - "))
    println(joinToString2(list, " , ", "["))
}