val oneToTen = 0..10

for(i in 0..100) {
 println(i)
}

>> 0
>> 1
>> 2
...
>> 100

/* Java */
for(int i = 0; i <= 100; i++) {
 println(i);
}

for(i in 100 downTo 0 step 2) {
 println(i)
}

>> 100
>> 98
>> 96
...
>> 0

/* Java */
for(int i = 100; i >= 0; i-=2) {
 println(i);
}

/* Java */
 HashMap<Integer, String> map = new HashMap<>();
map.put(1, "100");
map.put(2, "200");

Set<Integer> keySet = map.keySet();

for (int key : keySet) {
 System.out.println(" key:" + key + " value:" + map.get(key));
}

>> key:1 value:100
>> key:2 value:200

/* Kotlin */
val map = hashMapOf<Int, String>()\
map[1] = "100"
map[2] = "200"
for((key, value) in map) {
 println(" key:$key value:$value")
}

>> key:1 value:100
>> key:2 value:200

/* Java */
ArrayList<String> ls = new ArrayList<>();
ls.add("100");
ls.add("200");

// 只是迭代集合，打印集合中的数据
for(String str : ls) {
 System.out.println(str);
}

>> 100
>> 200

// 打印集合数据同时明确数据对应的下标
for(int i = 0; i < ls.size(); i++) {
 System.out.println("index:" + i + " value:" + ls.get(i));
}

>> index: 0 value: 100
>> index: 1 value: 200

/* Kotlin */
val ls = arrayListOf<String>()
ls.add("100")
ls.add("200")

for (i in 0 until ls.size) {
 println("index:$i value:${ls[i]}")
}

>> index: 0 value: 100
>> index: 1 value: 200

for ((index, value) in ls.withIndex()) {
 println("index:$index value:$value")
}

>> index: 0 value: 100
>> index: 1 value: 200

fun checkChar(c: Char) = when(c) {
 in '0'..'9' -> "number"
 in 'a'..'z', in 'A'..'Z' -> "string"
 else -> "don't know"
}

val num = if(n in 0..100) {
   n
   } else {
   throw IllegalArgumentException("The num value must between 0 and 100!")
   }

// 将一个字符串转换成数字，若不是数字，返回 null
fun transform(str: String) : Int? {
 try {
 return str.toInt()
 } catch(e: NumberFormatException) {
 return null
 }
}

// 上面的方法可以写作表达式体函数
fun transform(str: String) = try {
  str.toInt()
 } catch(e: NumberFormatException) {
  null
 }