Kotlin快速入门（二） 函数、boolean、字符串、if、when、loop、range、list和map

前言：作为一个安卓开发的老鸟，一步步从eclipse到AS开发安卓app，再到NDK开发，不断的更新，不断的学习，现如今Google把安卓的第一开发语言换成了Kotlin，所以我们也要紧跟Google步伐，转战kotlin，接下来我会带领大家快速入门kotlin开发。

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1.1函数

fun main(args:Array<String>){
	printstar(10)
	printstar(15)
	printstar()
}

fun printstar(i:Int){
	println("*"+i)
}

fun printstar(){
	println("**")
}

1.2函数-加减乘除

fun main(args:Array<String>){
	var m = 10
	var n = 5
	
	var p = plus(m, n)
	println("m+n = "+p)
	var s = sub(m, n)
	println("m-n = "+s)
	var mu = mutl(m, n)
	println("mxn = "+mu)
	var d = div(m, n)
	println("m/n = "+d)
}

//fun 函数名字(第一个int参数，第二个int参数)返回一个int值
fun plus(a:Int, b:Int):Int{
	return a+b;
}

fun sub(a:Int, b:Int):Int{
	return a-b;
}

fun mutl(a:Int, b:Int):Int{
	return a*b;
}

fun div(a:Int, b:Int):Int{
	return a/b;
}

2.boolean类型

fun main(args:Array<String>){
	var num1 = 4
	var num2 = 6
	println(num1 < num2)
	println(num1 > num2)
	
	var num3 = Math.sqrt(5.0) - Math.sqrt(4.0)
	var num4 = Math.sqrt(4.0) - Math.sqrt(3.0)
	println("num3 = "+num3)
	println("num4 = "+num4)
	println(num3 > num4)
	println(num3 < num4)
	
}

3.字符串操作（日记生成）

fun main(args:Array<String>){
	var diary = diaryGenerater("北京")
	println(diary);
    diary = diaryGenerater("杭州西湖")
	println(diary);
}

fun diaryGenerater(placeName:String):String{
	var temp = "我想去${placeName},所以要在百度搜<<${placeName}>> ${placeName.length}个字。"
	return temp
}

4.1if语句

//if else
fun main(args:Array<String>){
	var m = 10
	var n = 20
	println("${m}和${n}中大的数字是${retunBigNumber(m,n)}")
}


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

4.2if语句2

fun main(args:Array<String>){
	var face = checkFace(90)
	println(face)
	
	face = checkFace(60)
	println(face)
}

fun checkFace(score:Int):String{
	if(score>80){
		return "帅哥或者美女"
	}else{
		return "不是帅哥也不是美女"
	}
}

5.字符串比较

fun main(args:Array<String>){
	var str1 = "fly"
	var str2 = "FLY"
	
	println(str1.equals(str2)) 
	println(str1.equals(str2,true)) //忽略大小写
}

6.空值处理

fun main(args:Array<String>){
	var str1 = heat("123")
	println(str1)
	
	var str2 = heat(null)
	println(str2) //忽略大小写
}

//添加一个问号，表示可以传入一个null字符串
fun heat(str:String?):String{
	return "heat："+str
}

7.when语句

fun main(args:Array<String>){
	gradeStudent(90)
}

fun gradeStudent(score:Int){
	
	when(score){
		90 -> println("优秀")
		70 -> println("还可以")
		else -> println("加油")
	}
}

8.1loop和Range

fun main(args: Array<String>){
	var nums = 1 .. 100
	var result = 0
	for(num in nums){
		println(num)
		result = result + num
	}
	println("1到100的结果是${result}")
}

8.2loop和Range

fun main(args: Array<String>){
	var nums = 1 until 100
	var result = 0
	for(num in nums){
		println(num)
		result = result + num
	}
	println("1 until 100的结果是${result}")
}

8.3loop和Range

fun main(args: Array<String>){
	var nums = 1 .. 100
	for(num in nums step 2){
		println(num)
	}
	
	var nums2 = nums.reversed();
	for(num2 in nums2){
		println(num2)
	}
	
}

9.list

fun main(args: Array<String>){
	var lists = listOf("北京","上海","杭州","深圳")
	
	for ((i,e) in lists.withIndex()){
		println("$i  $e")
	}
}

10.map

import java.util.TreeMap

fun main(args: Array<String>){
	var map = TreeMap<String, String>()
	map["好好"] = "good good"
	map["学习"] = "study"
	map["天天"] = "day day"
	map["向上"] = "up"
	
	println(map["学习"])
}

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结束。。。。明天继续。