Kotlin中常见的List使用示例教程

fun main()
{
    val numbers = listOf(1, -2, 3, -4, 5, -6)
    val positives = numbers.filter { x -> x > 0 }
    val negatives = numbers.filter { it < 0 }      // 这里我们可以使用 it 
    println("positive values: ${positives}")        // 打印 positive values: [1, 3, 5]
    println("negative values: ${negatives}")        // 打印 positive values: [-2, -4, -6]
}

fun main()
{
    val numbers = listOf(1, -2, 3, -4, 5, -6)     
    val doubled = numbers.map { x -> x * 2 }
    val tripled = numbers.map { it * 3 }          
    println("doubled values: ${doubled}")       // 打印 doubled values: [2, -4, 6, -8, 10, -12]
    println("tripled values: ${tripled}")       // 打印 tripled values: [3, -6, 9, -12, 15, -18]
}

fun main()
{
    val numbers = listOf(1, -2, 3, -4, 5, -6)
    val totalCount = numbers.count() //集合中的元素总数                    
    val evenCount = numbers.count { it % 2 == 0 }  //与给定条件匹配的元素数      
    println("totalCount: ${totalCount}")    // 打印 totalCount: 6
    println("evenCount: ${evenCount}")      // 打印 evenCount: 3
}

fun main()
{
    val numbers = listOf(1, -2, 3, -4, 5, -6)            
    val first = numbers.first()                          
    val last = numbers.last()                            
    val firstEven = numbers.first { it % 2 == 0 }        
    val lastOdd = numbers.last { it % 2 != 0 }                  
    println("first element: ${first}")          // 打印 first element: 1
    println("last element: ${last}")            // 打印 last element: -6
    println("first Even element: ${firstEven}") // first Even element: -2
    println("last Odd element: ${lastOdd}")     // last Odd element: 5
}

fun main()
{
    val numbers = listOf(1, -2, 3, -4, 5, -6)            
    val anyNegative = numbers.any { it < 0 }             
    val anyGT6 = numbers.any { it > 6 }                  
    val allEven = numbers.all { it % 2 == 0 }            
    val allLess6 = numbers.all { it < 6 }  
    val allEven = numbers.none { it % 2 == 1 }           
    val allLess6 = numbers.none { it > 6 }               
    println("any negative elements: ${anyNegative}")    // 打印 any negative elements: true
    println("any elements larger than six: ${anyGT6}")  // any elements larger than six: false
    println("是否所有元素都是双数：${allEven}")           // 是否所有元素都是双数：false
    println("是否所有元素都小于6: ${allLess6}")           // 是否所有元素都小于6: true
}

fun main(string: Array<String>) {
    val test = listOf("one", "two", "three", "four", "five", "six")
    //从开头查询，字符长度大3的元素
    println(test.find {
        it.length > 2
    })
    println(test.findLast { it.length > 3 })
}
//输出
one
five

fun main(string: Array<String>) {
    val numbers = listOf(1, 2, 3, 4, 2, 5)
    println(numbers.indexOf(2))
    println(numbers.lastIndexOf(2))
}
//输出
1
4

fun main(string: Array<String>) {
    val numbers = mutableListOf("A", "B", "B", "C", "C", "A", "C")
    println(numbers.indexOfFirst { it == "A" })
    println(numbers.indexOfLast { it == "A" })
}
//输出
0
5

fun main(string: Array<String>) {
    //我们得到一个字符串数组
    val test = listOf("A", "B", "C", "D", "E", "F", "G")
    val temp = test.slice(listOf(1,4,3))
    println(temp)
}
//输出
[B, E, D]

fun main(string: Array<String>) {
    //我们得到一个字符串数组
    val test = listOf("A", "B", "C", "D", "E", "F", "G")
    //截取 下标从2 到4的 集合集
    val temp = test.slice(2..4)
    println(temp)
	//截取 步长为2的 指定区间的参数
    val temp1 = test.slice(2..4 step 2)
    println(temp1)
}
//输出
[C, D, E]
[C, E]

fun main(string: Array<String>) {
    //我们得到一个字符串数组
    val test = listOf("A", "B", "C", "D", "E", "F", "G")
    //从头截取
    val temp = test.take(5)
    println(temp)
    //从下标2的元素开始， 包括下标2的元素本身
    val temp1 = test.drop(2)
    println(temp1)
}
//输出
[A, B, C, D, E]
[C, D, E, F, G]