Kotlin 基础语法实例详解

package com.test.hello

import android.os.Bundle

val a: Int = 1
val b = 1 //类型自动推断为Int
val c: Int //没有初始化时必须指定类型
c = 1 //初始化

var x = 10
x = 3

fun sum(a: Int, b: Int): Int {
  return a + b
}

fun sum(a: Int, b: Int) = a + b

fun test(arg: String) {
  println(arg)
}

fun test(arg: String): Unit {
  println(arg)
}

fun min(a: Int, b: Int): Int {
  if (a > b) {
    return b
  } else {
    return a
  }
}

for
fun main(args: Array<String>) {
  for (arg in args) {
    println(arg)
  }
}

for (i in args.indices) {
  println(args[i])
}

fun main(args: Array<String>) {
  var i = 0
  while (i < args.size) {
    println(args[i++])
  }
}

fun case(a: Int) {
  when (a) {
    1 -> println("1")
     2 -> println("2")
     else -> println("else")
  }
}

if (x in 1..10) {
  // do
}

if (x !in 0..10) {
  //
}

for (x in 0..10) {
  //
}

if (name in names) { //names.contains()
  //
}

for (name in names) {
  println(name)
}

fun parseInt(str: String): Int? {
  // todo
}

fun main(args: Array<String>) {
  var name: String?
  val x = parseInt(args[0])
  if (x != null) { // check null
    // todo
  }
}

fun getStringLength(obj: Any): Int? {
  if (obj is String && obj.length > 0) {
    return obj.length // obj as String after is
  }
  return null
}