Kotlin学习（1）概述

变量和常量

//String类型，自动判断类型(不可变变量Value)val laugh = "lalalalala"//浮点类型，默认Doubleval PI = 3.1415//Float类型val PI_FLOAT = 3.1415F//一旦赋值后不能改变，但是可以条件赋值val msg: Int = min(2,1)//可变类型(Variable)var status = 0fun block(){    //但类型不能改变,以下语句报错    //status = "aaa"}

函数

//参数和返回值都是写在: 后面fun max(a: Int, b: Int): Int {    //if...else可代替？：    return if (a > b) a else b}//函数也不用写在里面//短函数块，还是能用=fun min(a: Int, b: Int): Int = if (a > b) b else a

类的定义

/**class Test(val name: String = "Test")==>等价于public class Person{    private final String name;    public Person(String name){        this.name = name;    }    public String getName(){        return name;    }}//val只有getter方法//var有getter和setter方法 *///这是个默认构造器,并且可以赋个默认值class Test(val name: String = "Test") {    //参数和返回值都是写在: 后面    fun max(a: Int, b: Int): Int {        //if...else可代替？：        return if (a > b) a else b    }}class Rectangle(val height: Int, val width: Int){    //自定义getter方法    val isSquare: Boolean        get() = height == width}fun createRec(): Rectangle{    val random = Random()    return Rectangle(random.nextInt(),random.nextInt())}

main函数和模板字符串

//main函数已经不能写在Class里面了fun main(args: Array<String>) {    val max = Test().max(1,2)  //和Java类似    //字符串模板    println("The max is $max")    println("The min is ${min(1,2)}")    println(max is Int)               //类似于instanceof}

继承和接口

interface Exprclass Num(val value: Int) : Exprclass Sum(val left: Expr, val right: Expr) : Exprfun eval(e: Expr): Int{    if (e is Num){        //此处不用显性类型转化        val n = e //as Num        return n.value    }    if (e is Sum){        //在e is Sum为True时，该作用域内自动转化        return eval(e.left) + eval(e.right)    }    throw IllegalArgumentException()}fun eval2(e: Expr): Int =        when (e){            is Num -> {                println("num: ${e.value}")                e.value            }            is Sum -> {                val left = eval2(e.left)                val right = eval2(e.right)                println("sum: $left + $right")                left + right            }            else -> throw IllegalArgumentException()        }fun main(args: Array<String>){    val a = eval2(Sum(Sum(Num(1),Num(2)),Num(4)))    println(a)}

Enum和when

//枚举类enum class Color (        val r: Int,        val g: Int,        val b: Int){    RED(255,0,0),    ORANGE(255,165,0),    GREEN(0,255,0),    YELLOW(0,0,255),    BLUE(0,0,255),    JAOSDHO(161,18,25);    fun rgb() = (r * 256 + g) * 256 + b    //when来代替switch    fun getMnemonic(color: Color) =            when (color){                BLUE -> "Blue"                GREEN -> "Green"                ORANGE,RED -> "Red or Orange"                else -> "fuck color"            }    fun mixColor(c1: Color, c2: Color) =            when (setOf<Color>(c1, c2)){                setOf(RED,YELLOW) -> ORANGE                setOf(YELLOW,BLUE) -> GREEN                else -> throw Exception("Unknown Color")            }    fun maxColor2(c1: Color, c2: Color): Color{        when{            (c1 == RED && c2 == YELLOW) ||                    (c1 == YELLOW && c2 == RED) ->            return ORANGE            else -> throw Exception("Unknown Color")        }    }}

迭代和in

可以使用传统的while(){…}或do{…}while()

fun main(args: Array<String>){    //class kotlin.ranges.IntRange    val oneToTen = 1..10            //包括10    val oneToSize = 1 until 10      //不包括10    val tenToOne = 10 downTo 1      //包括1    val stepTwo = 1..10 step 2      //1,3,5,7,9    //class kotlin.ranges.CharRange    val charIter = 'A'..'F'    //test IntRange    for (i in stepTwo){        //println(i)    }    //Map上的迭代    val sortedMap = TreeMap<Char,String>()    //test Map    for (c in 'A'..'F'){        //可以以Python的方式访问和赋值        sortedMap[c] = Integer.toBinaryString(c.toInt())    }    for ((k,v) in sortedMap){        println("$k = $v")    }    //List上的迭代    val list = arrayListOf("10","11","1001")    for ((index,ele) in list.withIndex()){        println("$index : $ele")    }    //使用in来判断,使用的是Comparable接口的c    fun isLetter(c: Char) = c in 'a'..'z' || c in 'A'..'Z'    fun isNotDigit(c: Char) = c !in '0'..'9'    println("KCK" in "J".."L")                  //true,K在J,L中间    println("Kotlin" in setOf("Java","Scala"))  //false}

try…catch…finally

可以和Java一样的用法

或作为表达式

fun readNumber(read: BufferedReader){    //try{}作为表达式    val number = try {        Integer.parseInt(readLine())    }catch (e: NumberFormatException){        return    }}