kotlin方法命名

java的main方法

 public static void main(String args[]) { 
        System.out.println("Hello World!"); 
    }

kotlin的main方法

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

kotlin循环

 /**
     *  kotlin循环
     * */
    fun looptest(){
        var nums=1..10//表示1到100的数组
        var result=0
       for(num in nums){//同javafor循环遍历数组
           result=result+num
       }
        Log.i("kotlin","result=${result}")//打印可以直接${result} $符号后面的花括号里面的变量可以直接取值
    }

打印结果2020-08-20 11:01:24.360 12457-12457/com.example.myapplication I/kotlin: result=55

kotlin区间

/**
     *  kotlin区间
     * */
    fun qujianTest(){
        var nums=1 until  10  //1到10不包括10
        var result=0
        for(num in nums){
            Log.i("num=","${num}")
        }
        //奇数1到16里面的
        var num2=1..16
        for(a in num2 step 2){
            Log.i("a","${a}")
        }
        //数组的倒序，1到16变成16到1
        var num3=num2.reversed()
        for(b in num3 ){
            Log.i("b","${b}")
        }
        //查看数组里面元素个数
        Log.i("num3","${num3.count()}")
    }

1到10不包括10
2020-08-20 11:01:24.367 12457-12457/com.example.myapplication I/kotlin: num=1
2020-08-20 11:01:24.368 12457-12457/com.example.myapplication I/kotlin: num=2
2020-08-20 11:01:24.368 12457-12457/com.example.myapplication I/kotlin: num=3
2020-08-20 11:01:24.368 12457-12457/com.example.myapplication I/kotlin: num=4
2020-08-20 11:01:24.368 12457-12457/com.example.myapplication I/kotlin: num=5
2020-08-20 11:01:24.368 12457-12457/com.example.myapplication I/kotlin: num=6
2020-08-20 11:01:24.368 12457-12457/com.example.myapplication I/kotlin: num=7
2020-08-20 11:01:24.369 12457-12457/com.example.myapplication I/kotlin: num=8
2020-08-20 11:01:24.369 12457-12457/com.example.myapplication I/kotlin: num=9
1到16之间的奇数
2020-08-20 11:01:24.371 12457-12457/com.example.myapplication I/kotlin: a=1
2020-08-20 11:01:24.372 12457-12457/com.example.myapplication I/kotlin: a=3
2020-08-20 11:01:24.372 12457-12457/com.example.myapplication I/kotlin: a=5
2020-08-20 11:01:24.372 12457-12457/com.example.myapplication I/kotlin: a=7
2020-08-20 11:01:24.372 12457-12457/com.example.myapplication I/kotlin: a=9
2020-08-20 11:01:24.372 12457-12457/com.example.myapplication I/kotlin: a=11
2020-08-20 11:01:24.373 12457-12457/com.example.myapplication I/kotlin: a=13
2020-08-20 11:01:24.373 12457-12457/com.example.myapplication I/kotlin: a=15
3.1到16数组倒序
2020-08-20 11:01:24.373 12457-12457/com.example.myapplication I/kotlin: 16
2020-08-20 11:01:24.373 12457-12457/com.example.myapplication I/kotlin: 15
2020-08-20 11:01:24.373 12457-12457/com.example.myapplication I/kotlin: 14
2020-08-20 11:01:24.373 12457-12457/com.example.myapplication I/kotlin: 13
2020-08-20 11:01:24.373 12457-12457/com.example.myapplication I/kotlin: 12
2020-08-20 11:01:24.373 12457-12457/com.example.myapplication I/kotlin: 11
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 10
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 9
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 8
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 7
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 6
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 5
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 4
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 3
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 2
2020-08-20 11:01:24.374 12457-12457/com.example.myapplication I/kotlin: 1
1到16数组，数组的长度
2020-08-20 11:01:24.402 12457-12457/com.example.myapplication I/kotlin: 16

kotlin list入门

fun listTest(){
        var lists= listOf<String>("买鸡蛋","杜蕾斯","买土豆")
        for((i,e)in lists.withIndex()){
            Log.i("kotlin","${i} ${e}")
        }
    }

5.list数组第几项对应什么元素
2020-08-20 11:01:24.414 12457-12457/com.example.myapplication I/kotlin: 0 买鸡蛋
2020-08-20 11:01:24.414 12457-12457/com.example.myapplication I/kotlin: 1 杜蕾斯
2020-08-20 11:01:24.414 12457-12457/com.example.myapplication I/kotlin: 2 买土豆

kotlin map入门

 fun mapTest(){
        var map= TreeMap<String,String>()
        map["好"]="good"
        map["学"]="fuck"
        Log.i("kotlin","${map["好"]}")
    }

结果输出
2020-08-20 11:01:24.415 12457-12457/com.example.myapplication I/kotlin: good

kotlin 函数和函数表达式

 fun add(x:Int,y:Int):Int{
        Log.i("kotlin","${x+y}"+"函数表达式一")

       return x+y
    }
 fun addTwo(x:Int,y:Int):Int= x+y
 fun addThree(){
        var i={x:Int,y:Int ->x+y}
        var result=i(3,5)
        Log.i("kotlin","${result}"+"函数表达式三")
    }
 fun addFour(){
       var j:(Int,Int)->Int={x,y->x+y}
        var result=j(3,5)
        Log.i("kotlin","${result}"+"函数表达式四")
    }

2020-08-20 11:01:24.415 12457-12457/com.example.myapplication I/kotlin: 8函数表达式一
2020-08-20 11:01:24.415 12457-12457/com.example.myapplication I/kotlin: 8函数表达式二
2020-08-20 11:01:24.416 12457-12457/com.example.myapplication I/kotlin: 8函数表达式三
2020-08-20 11:01:24.416 12457-12457/com.example.myapplication I/kotlin: 8函数表达式四

kotlin 默认参数和具名参数

 fun 获取长方形周长(a:Float,b:Float):Float{
        Log.i("kotlin","${a*b}"+"获取长方形周长")
        return a*b
        // a=3.3f,b=5.5
    }

2020-08-20 11:01:24.417 12457-12457/com.example.myapplication I/kotlin: 18.15获取长方形周长

   fun 获取圆周长(PI:Double,圆的半径:Float):Double{
        Log.i("kotlin","${2*PI*圆的半径}"+"获取圆周长")
        return 2*PI*圆的半径
    }
//  获取圆周长(PI,4.0f)

2020-08-20 11:40:00.409 16996-16996/com.example.myapplication I/kotlin: 25.132741228718345获取圆周长

    fun 获取圆柱体体积(PI:Double,圆的半径:Float,高:Float):Double{
        Log.i("kotlin","${PI*圆的半径*圆的半径*高}"+"获取圆柱体体积")
        return PI*圆的半径*圆的半径*高
    }
//    获取圆柱体体积(PI,4.0f,4.0f)

2020-08-20 11:40:00.410 16996-16996/com.example.myapplication I/kotlin: 201.06192982974676获取圆柱体体积

Demo github地址

kotlin学习笔记

kotlin学习笔记

kotlin方法命名