Kotlin for 循环写法整理

Posted android阿杜

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1、Map 的 in 运算符方式:

fun forMap1() 
    val map = hashMapOf<String, String>("name" to "Hili", "age" to "93")
    for ((k, v) in map) 
        println("$k -> $v")
    

输出:

name -> Hili
age -> 93

 

 

2、List 的 in 运算符方式:

fun forList1() 
    val list = listOf("apple", "banana", "kiwifruit")

    for (item in list) 
        println(item)
    

输出:

apple
banana
kiwifruit

 

 

3、List 的 in 运算符方式,带上数据类型:

fun forList2() 
    val list = listOf("apple", "banana", "kiwifruit")

    for (item: String in list) 
        println(item)
    

输出:

apple
banana
kiwifruit

 

 

4、List 的 indices 索引方式:

fun forList3() 
    val list = listOf("apple", "banana", "kiwifruit")

    for (index in list.indices) 
        val str = "item at $index is $list[index]"
        println(str)
    

输出:

item at 0 is apple
item at 1 is banana
item at 2 is kiwifruit

 

 

5、List 的 withIndex() 库函数方式:

fun forList4() 
    val list = listOf("apple", "banana", "kiwifruit")

    // 库函数 withIndex() 获取索引
    for ((i, v) in list.withIndex()) 
        val str = "the element at $i is $v"
        println(str)
    

输出:

the element at 0 is apple
the element at 1 is banana
the element at 2 is kiwifruit

 

 

6、Array 的 in 运算符方式(同 List):

fun forArray1() 
    val array = arrayOf("java", "c plus plus", "kotlin", "python")

    for (item in array) 
        println(item)
    

输出:

java
c plus plus
kotlin
python

 

 

7、Array 的 in 运算符方式,带上数据类型(同 List):

fun forArray2() 
    val array = arrayOf("java", "c plus plus", "kotlin", "python")

    for (item: String in array) 
        println(item)
    

输出:

java
c plus plus
kotlin
python

 

 

8、Array 的 indices 索引方式(同 List):

fun forArray3() 
    val array = arrayOf("java", "c plus plus", "kotlin", "python")

    for (index in array.indices) 
        val str = "item at $index is $array[index]"
        println(str)
    

输出:

item at 0 is java
item at 1 is c plus plus
item at 2 is kotlin
item at 3 is python

 

 

9、Array 的 withIndex() 库函数方式(同 List):

fun forArray4() 
    val array = arrayOf("java", "c plus plus", "kotlin", "python")

        // 库函数 withIndex() 获取索引
    for ((i, v) in array.withIndex()) 
        val str = "the element at $i is $v"
        println(str)
    

输出:

the element at 0 is java
the element at 1 is c plus plus
the element at 2 is kotlin
the element at 3 is python

 

 

10、.. (rangeTo()) 方式:

fun forRange1() 
    for (item in 1..5) 
        print(item)
    

输出:

1
2
3
4
5

 

 

11、.. (rangeTo())  step 方式:

fun forRange2() 
    for (item in 0..10 step 3) 
        print(item)
    

输出:

0
3
6
9

 

 

12、.. (rangeTo())  downTo 方式:

fun forRange3() 
    for (item in 10 downTo 0) 
        print(item)
    

输出:

10
9
8
7
6
5
4
3
2
1
0

 

 

13、.. (rangeTo())  downTo step方式:

fun forRange4() 
    for (item in 10 downTo 0 step 3) 
        print(item)
    

输出:

10
7
4
1

 

 

14、until [闭,开) 区间方式:

fun forRange5() 
    for (item in 0 until 10) 
        print(item)
    

输出:

0
1
2
3
4
5
6
7
8
9

 

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