kotlin笔记_基础

变量和函数

package com.example.helloworld

import kotlin.math.max

// val, var, fun
fun main()
{
//    println("Hello Kotlin!")

//    val a = 10
//    println("a = " + a)

//    var a: Int = 10
//    a = a * 10
//    println("a = " + a)

    val a = 37
    val b = 40
    val value = largerNumber1(a, b)
    println("larget number is " + value)
}

fun largerNumber1(num1: Int, num2: Int) = max(num1, num2)
//fun largerNumber1(num1: Int, num2: Int): Int = max(num1, num2)
//fun largerNumber1(num1: Int, num2: Int): Int
//{
//    return max(num1, num2)
//}

if语句

package com.example.helloworld

// if
fun main()
{
    println(largerNumber2(10, 11))
}

// 1
//fun largerNumber2(num1: Int, num2: Int): Int
//{
//    var value = 0
//    if (num1 > num2) {
//        value = num1
//    } else {
//        value = num2
//    }
//    return value
//}

// 2
//fun largerNumber2(num1: Int, num2: Int): Int
//{
//    val value = if (num1 > num2) {
//        num1
//    } else {
//        num2
//    }
//    return value
//}

// 3
//fun largerNumber2(num1: Int, num2: Int): Int
//{
//    return if (num1 > num2) {
//        num1
//    } else {
//        num2
//    }
//}

// 4
//fun largerNumber2(num1: Int, num2: Int) = if (num1 > num2) {
//    num1
//} else {
//    num2
//}
fun largerNumber2(num1: Int, num2: Int) = if (num1 > num2) num1 else num2

when语句

package com.example.helloworld

// when
fun main()
{
    println(getScore("Tom"))
    println(getScore2("Tommy"))


    println(checkNumber(10))
    println(checkNumber(10L))

}

// 1
//fun getScore(name: String) = if (name == "Tom") {
//    86
//} else if (name == "Jim") {
//    77
//} else if (name == "Jack") {
//    95
//} else if (name == "Liky") {
//    100
//} else {
//    0
//}

// 2
fun getScore(name: String) = when (name) {
    "Tom" -> 86
    "Jim" -> 77
    "Jack" -> 95
    "Lily" -> 100
    else -> 0
}

fun checkNumber(num: Number)
{
    when (num) {
        is Int -> println("number is Int")
        is Double -> println("number is Double")
        else -> println("number not support")
    }
}

// 所有以"Tom"开头的名字都是86
fun getScore2(name: String) = when {
    name.startsWith("Tom") -> 86
    name == "Jim" -> 77
    name == "Jack" -> 95
    name == "Lily" -> 100
    else -> 0
}

循环语句

package com.example.helloworld

// for
fun main()
{
//    for (i in 0..10) {
//        println(i)
//    }

//    for (i in 0 until 10) {
//        println(i)
//    }

//    for (i in 0..10 step 2) {
//        println(i)
//    }

//    for (i in 10 downTo 1) {
//        println(i)
//    }

    for (i in 10 downTo 1 step 2) {
        println(i)
    }
}

参考

郭霖. 《第一行代码 Android 第3版》