Kotlin 基础语法

变量声明

常量: val + 常量名

变量: var + 变量名

val a = 10
var b = 10

输出

var a = 10 
println("a = $a")

集合

List系列

声明方法

只读 List 声明 val listname = listOf()

可变List 声明 val listname:MutableList<String> = mutableListOf()

// Read only list
val readOnlyShapes = listOf("triangle", "square", "circle")
println(readOnlyShapes)
// [triangle, square, circle]

// Mutable list with explicit type declaration
val shapes: MutableList<String> = mutableListOf("triangle", "square", "circle")
println(shapes)
// [triangle, square, circle]

相关方法

条件控制

if表达式

var a:int = 10
var b:int = 11
if(a < b ){
    println("a大")
}else{
    println("b大")
}

可以赋值给变量

val max = if (a > b) {
    print("Choose a")
    a
} else {
    print("Choose b")
    b
}

判断区间

var a:int = 10

if ( a in 9..11){
    println("True")
}

When表达式

when (x) {
    1 -> print("x == 1")
    2 -> print("x == 2")
    else -> { // 注意这个块
        print("x 不是 1 ，也不是 2")
    }
}

相当于C语言里的switch

还可以用in检测是否在一个区间中

when (x) {
    in 1..10 -> print("x is in the range")
    in validNumbers -> print("x is valid")
    !in 10..20 -> print("x is outside the range")
    else -> print("none of the above")
}

循环

指定步长

for (i in 1..10){
    println(i)
}
// 1234 .... 10

for (i in 1..10 step 2){
    println(i)
}
// 13579

for (i in 1 until 10){
    println(i)
}
// 12345..9

迭代对象

for(item in items){
    println(item)
}

同样也有break continue return