1.创建DTOs(POJOs/POCOs)
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data class Customer(val name: String, val email: String)
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创建一个Customer类需要提供下面功能：
getters 为所有的属性提供getters(为var类型提供setters, val类型不可变，不需要提供)
equals()
hashcode()
toString()
copy()
component1(), component2(), …, for all properties (see Data classes)
2. 为函数提供默认参数
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fun foo(a: Int = 0, b: String){
println("a: ${a}, b: ${b}")
} |
3. 过滤一个列表
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var posi = lists.filter { a->a.startsWith('a') }
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或者更简洁：
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posi = lists.filter { it.startsWith('a') }
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4. String插入
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println("Name $name")
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5. 示例检查
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when (x) { is Foo -> ...
is Bar -> ...
else -> ...
} |
6. 打印map和或者list
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var maps = mapOf("a" to 1, "b" to 2, "c" to 3)
for((k,v) in maps){
println("k: ${k}, v: ${v}")
} |
7. 使用'范围'
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for(i in 1..100) {
print("${i} ")
} for(i in 1 until 10) {
} for(x in 1..10 step 2) {
} for(x in 10 downTo 1) {
} var x = 3
if (x in 1..10) {
println("xxx in")
} |
8. 只读list（注意var和val区别）
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val list = listOf("a", "b", "c")
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9. 只读map
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val map = mapOf("a" to 1, "b" to 2, "c" to 3)
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10. 访问map
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var maps = mapOf("a" to 1, "b" to 2, "c" to 3)
println(maps["b"])
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11. 懒汉式属性？
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val p: String by lazy { // compute the string
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12. 扩展功能（个人觉得比较强大，类似于注入？）
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fun String.testAddMethod(){ println(this)
} "abcd".testAddMethod()
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13. 单例
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object Resource { val name = "name Resource"
} |
14. if != null的快速写法
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val files = listOf("a", "b", "c")
println(files?.size) |
15. if else 快速写法
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fun getNil():String?{ return null
}fun main(args: Array<String>) { var files = getNil()
println(files?.length?: "empty")
} |
16. 如果为null执行一段语句
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files?:println("is null")
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17. 如果不为null执行一段语句
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files?.let { println("not null") }
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18. 通过when语句返回
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var string = "b"
println(when(string) { "a" ->0
"b" ->1
else -> 100
}) |
19. try/catch表达式
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fun test() { val result = try {
count()
} catch (e: ArithmeticException) {
throw IllegalStateException(e)
} // Working with result}
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20. if表达式
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val a = 2
var result = if(a == 1) {
"one"
} else if(a == 2) {
"two"
}else {
"three"
} |
21. 使用构造者模式
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fun arrayMinusOnes(size: Int):IntArray { return IntArray(size).apply { fill(-1) }
} |
22. 单一表达式函数
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fun single(size: Int) = size * 10
相当于是：fun single(size: Int): Int { return size * 4
}这个可以和其他约定一起组合，产生更简短的代码，比如when表达式：fun transfrom(color: Int):String = when (color) { 1-> "red"
2-> "blue"
else-> "other color"
} |
23. 调用一个对象的多个方法使用with
省略了obj.xxx()
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fun main(args: Array<String>) { val kotlin = RunKotlin()
with(kotlin) {
penDown()
println("zzz")
forward(2.0)
}
}class RunKotlin {
fun penDown(){println("penDown")}
fun penUp(){println("penUp")}
fun turn(degress: Double){println(degress)}
fun forward(pixels: Double){println(pixels)}
} |
24. Java 7's try with resources
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val stream = Files.newInputStream(Paths.get("/some/file.txt"))
stream.buffered().reader().use { reader -> println(reader.readText())
} |
25. Convenient form for a generic function that requires the generic type information
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/ public final class Gson {
// ...// public <T> T fromJson(JsonElement json, Class<T> classOfT) throws JsonSyntaxException {// ...inline fun <reified T: Any> Gson.fromJson(json): T = this.fromJson(json, T::class.java)
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26. 构造可能为null的布尔值
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val b: Boolean? = ...if (b == true) {
...
} else {
// `b` is false or null
} |
本文转自rongwei84n 51CTO博客，原文链接：http://blog.51cto.com/483181/1931893，如需转载请自行联系原作者