- 变量的声明。
//java
int a;
int a=0;
final a=1;
//kotlin
var a
var a : Int
var a=0
var a : Int =0
val a=1
- 字符串拼接：
//java
int a=0;
int b=1;
String str="a="+a+",b="+b
//kotlin
var a=0
var b=1
var str:String ="a= $a,b= $b"
- 函数构建
//java
public int createFunction(int a,String b){
return a+b;
}
//kotlin “？”表示可以返回空值
fun createFunction(a:int=0,b:String="Hi" )：Int？{
return a+b
}
fun createFunction(a:Int,b:Int)=a+b
- 使用循环
//java
String[] strs={"aa","bb","cc","dd"};
for（int i=0;i<a.length;i++）{
}
for(String str:strs){
}
//kotlin
val items = listOf("apple", "banana", "kiwi")
for (item in items) {
println(item)
}
for (index in items.indices) {
println("item at $index is ${items[index]}")
}
- Kotlin的Win表达式
fun describe(obj: Any): String =
when (obj) {
1 -> "One"
"Hello" -> "Greeting"
is Long -> "Long"
!is String -> "Not a string"
else -> "Unknown"
}
fun main(args: Array<String>) {
println(describe(1))
println(describe("Hello"))
println(describe(1000L))
println(describe(2))
println(describe("other"))
}
- Kotlin的in关键字
//判断变量是否在range之中
fun main(args: Array<String>) {
val x = 10
val y = 9
if (x in 1..y+1) {
println("fits in range")
}
}
fun main(args: Array<String>) {
val list = listOf("a", "b", "c")
if (-1 !in 0..list.lastIndex) {
println("-1 is out of range")
}
if (list.size !in list.indices) {
println("list size is out of valid list indices range too")
}
}
//在范围内迭代：
for (x in 1..5) {
print(x)
}
//或者使用步进：
for (x in 1..10 step 2) {
print(x)
}
for (x in 9 downTo 0 step 3) {
print(x)
}
//使用 in 操作符检查集合中是否包含某个对象
val items = setOf("apple", "banana", "kiwi")
when {
"orange" in items -> println("juicy")
"apple" in items -> println("apple is fine too")
}
