1.创建DTOs(POJOs/POCOs)
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1
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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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3
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fun foo(a: Int =
0
, b: String){
println(
"a: ${a}, b: ${b}"
)
}
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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
-> ...
}
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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: ${v}"
)
}
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7. 使用'范围'
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for
(i in
1
..
100
) {
print(
"${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"
)
}
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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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2
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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"
}
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14. if != null的快速写法
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val files = listOf(
"a"
,
"b"
,
"c"
)
println(files?.size)
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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"
)
}
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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
})
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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"
}
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21. 使用构造者模式
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fun arrayMinusOnes(size: Int):IntArray {
return
IntArray(size).apply { fill(-
1
) }
}
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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"
}
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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)}
}
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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())
}
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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
}
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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
