1.也是有三种方法，与创建list和set集合类似

fun main(args: Array<String>) {
    //固定不可变的map
    val map = mapOf<String, String>("中国" to "China", "英国" to "England", "美国" to "USA")
    map.forEach { println(it) }
    //可变的map
    val mutableListOf = mutableMapOf<String, String>("中国" to "China", "英国" to "England")
    mutableListOf["美国"] = "USA"
    mutableListOf.put("124", "124")
    mutableListOf.forEach { println(it) }
    //java中的map
    val hashtable = Hashtable<String, String>()
    hashtable["中国"] = "China"
    hashtable["英国"] = "England"
    hashtable.put("124", "124")
    hashtable.forEach { println(it) }
}

2.map的四种遍历方式

fun main(args: Array<String>) {
    //固定不可变的map
    val map = mapOf<String, String>("中国" to "China", "英国" to "England", "美国" to "USA")
    //遍历所有的key值
    val keySet = map.keys
    keySet.forEach { println(it) }

    //遍历所有的value
    val values = map.values
    values.forEach { println(it) }

    //key值和value值全部遍历出来
    map.forEach { key, value -> println("key=$key  Value=$value") }

    for ((key: String, value: String) in map) {
        println("key=$key  Value=$value")
    }
}