第3章 Kotlin语言基础 《Kotlin 极简教程》

第3章 Kotlin语言基础

3.1 包（package）

package

package com.abc.fastjson

package com.bbc.jackjson

com.abc.fastjson.JSON.toJSONString()
com.bbc.jackjson.JSON.parseJSONObject()

package

*.kt

package

package com.easy.kotlin

/**
* Created by jack on 2017/6/8.
*/

fun what(){
println("This is WHAT ?")
}

class Motorbike{
fun drive(){
println("Drive The Motorbike ...")
}
}

fun main(args:Array<String>){
println("Hello,World!")
}

com.easy.kotlin

what()

Motorbike

src/test/kotlin

src/main/kotlin

package com.easy.kotlin

package com.easy.kotlin

import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

/**
* Created by jack on 2017/6/8.
*/

@RunWith(JUnit4::class)
class PackageDemoTest {

@Test
fun testWhat() {
what()
}

@Test
fun testDriveMotorbike(){
val motorbike = Motorbike()
motorbike.drive()
}

}

what()

PackageDemoTest

import

Motorbike

PackageDemoTest

src/test/kotlin

package com.easy.kotlin.test

package com.easy.kotlin

package com.easy.kotlin.test

import com.easy.kotlin.Motorbike
import com.easy.kotlin.what
import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

/**
* Created by jack on 2017/6/8.
*/

@RunWith(JUnit4::class)
class PackageDemoTest {

@Test
fun testWhat() {
what()
}

@Test
fun testDriveMotorbike() {
val motorbike = Motorbike()
motorbike.drive()
}

}

import com.easy.kotlin.Motorbike

import com.easy.kotlin.what

build.gradle

testCompile group: 'junit', name: 'junit', version: '4.12'

src/main/kotlin

import java.util.*

/**
* Created by jack on 2017/6/8.
*/

fun now() {
println("Now Date is: " + Date())
}

class Car{
fun drive(){
println("Drive The Car ... ")
}

}

src/test/kotlin

import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

/**
* Created by jack on 2017/6/8.
*/

@RunWith(JUnit4::class)
class DefaultPackageDemoTest {

@Test
fun testDefaultPackage() {
now()
val car = Car()
car.drive()
}

}

now()

Car

src/test/kotlin/com/easy/kotlin/PackageDemoTest.kt

now()

Car

import now
import Car

package com.easy.kotlin

import now
import Carimport org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

/**
* Created by jack on 2017/6/8.
*/

@RunWith(JUnit4::class)
class PackageDemoTest {

@Test
fun testWhat() {
what()
}

@Test
fun testDriveMotorbike(){
val motorbike = Motorbike()
motorbike.drive()
}

@Test
fun testDefaultPackage() {
now()
val car = Car()
car.drive()
}

}

3.2 声明变量和值

var

val

var

val

package com.easy.kotlin

import java.util.*

/**
* Created by jack on 2017/6/8.
*/

class VariableVSValue {
fun declareVar() {
var a = 1
a = 2
println(a)
println(a::class)
println(a::class.java)

var x = 5 // 自动推断出 `Int` 类型
x += 1

println("x = $x")
}

fun declareVal() {
val b = "a"
//b  = "b" //编译器会报错： Val cannot be reassigned
println(b)
println(b::class)
println(b::class.java)

val c: Int = 1  // 立即赋值
val d = 2   // 自动推断出 `Int` 类型
val e: Int  // 如果没有初始值类型不能省略
e = 3       // 明确赋值
println("c = $c, d = $d, e = $e")
}
}

val

3.3 变量类型推断

3.3.1 省去变量类型

fun typeInference(){
val str = "abc"
println(str)
println(str is String)
println(str::class)
println(str::class.java)

//        abc
//        true
//        class java.lang.String (Kotlin reflection is not available)
//        class java.lang.String

val d = Date()
println(d)
println(d is Date)
println(d::class)
println(d::class.java)

//        Fri Jun 09 00:06:33 CST 2017
//        true
//        class java.util.Date (Kotlin reflection is not available)
//        class java.util.Date

val bool = true
println(bool)
println(bool::class)
println(bool::class.java)

//        true
//        boolean (Kotlin reflection is not available)
//        boolean

val array = arrayOf(1,2,3)
println(array)
println(array is Array)
println(array::class)
println(array::class.java)

//        [Ljava.lang.Integer;@7b5eadd8
//        true
//        class [Ljava.lang.Integer; (Kotlin reflection is not available)
//        class [Ljava.lang.Integer;
}

fun Int2Long(){
val x:Int = 10
val y:Long = x // Type mismatch
}

fun Int2Long(){
val x:Int = 10
//        val y:Long = x // Type mismatch
val y: Long = x.toLong()
}

3.3.2 使用

is

运算符进行类型检测

is

fun getLength(obj: Any): Int? {
var result = 0
if (obj is String) {
// `obj` 在该条件分支内自动转换成 `String`
println(obj::class) //class java.lang.String
result = obj.length
println(result)
}
// 在离开类型检测分支后，`obj` 仍然是 `Any` 类型
println(obj::class) // class java.lang.Object
return result
}

@Test
fun testGetLength() {
val obj = "abcdef"
val len = variableVSValue.getLength(obj)
Assert.assertTrue(len == 6)

val obj2:Any = Any()
variableVSValue.getLength(obj2)

}

3.4 字符串与其模板表达式

package com.easy.kotlin

/**
* Created by jack on 2017/6/9.
*/

fun main(args: Array<String>) {
val rawString = """
fun helloWorld(val name : String) {
println("Hello, world!")
}
"""
println(rawString)

}

val fooTemplateString = "$rawString has ${rawString.length} characters"
println(fooTemplateString)

3.5 流程控制语句

if

when

for

while

return

break

continue

throw

3.5.1 if表达式

package com.easy.kotlin

/**
* Created by jack on 2017/6/9.
*/

fun main(args: Array<String>) {
println(max(1, 2))
}

fun max(a: Int, b: Int): Int {

// 作为表达式
val max = if (a > b) a else b
return max //  return if (a > b) a else b
}

fun max1(a: Int, b: Int): Int {
// 传统用法
var max1 = a
if (a < b) max1 = b
return max1

}

fun max2(a: Int, b: Int): Int {

// With else
var max2: Int
if (a > b) {
max2 = a
} else {
max2 = b
}
return max2
}

fun max3(a: Int, b: Int): Int {
val max = if (a > b) {
print("Max is a")
a
} else {
print("Max is b")
b
}
return max
}

true? 1: 0

if else

if(true) 1 else 0

>>> val x = if(1==1) true
>>> x
kotlin.Unit
>>> val y = if(1==1) true else false
>>> y
true

>>> if("a") 1
error: type mismatch: inferred type is String but Boolean was expected
if("a") 1
^

>>> if(1) println(1)
error: the integer literal does not conform to the expected type Boolean
if(1)
^

>>> if(true) println(1) else println(0)
1
>>> if(true) { println(1)}  else{ println(0)}
1

3.5.2 when表达式

fun cases(obj: Any) {
when (obj) {
1 -> print("第一项")
"hello" -> print("这个是字符串hello")
is Long -> print("这是一个Long类型数据")
!is String -> print("这不是String类型的数据")
else -> print("else类似于Java中的default")
}
}

fun switch(x: Any) {
when (x) {
-1, 0 -> print("x == -1 or x == 0")
1 -> print("x == 1")
2 -> print("x == 2")
else -> { // 注意这个块
print("x is neither 1 nor 2")
}
}
}

fun switch(x: Int) {
val s = "123"
when (x) {
-1, 0 -> print("x == -1 or x == 0")
1 -> print("x == 1")
2 -> print("x == 2")
8 -> print("x is 8")
parseInt(s) -> println("x is 123")
else -> { // 注意这个块
print("x is neither 1 nor 2")
}
}
}

val x = 1
val validNumbers = arrayOf(1, 2, 3)
when (x) {
in 1..10 -> print("x is in the range")
in validNumbers -> print("x is valid")
!in 10..20 -> print("x is outside the range")
else -> print("none of the above")
}

3.5.3 for循环

for (item in collection) {
print(item)
}

for (i in intArray) {
...
}

/**
* For loop iterates through anything that provides an iterator.
* See http://kotlinlang.org/docs/reference/control-flow.html#for-loops */
fun main(args: Array<String>) {
for (arg in args)
println(arg)
// or
println()
for (i in args.indices)
println(args[i])
}

for (i in array.indices) {
print(array[i])
}

withIndex

for ((index, value) in array.withIndex()) {
println("the element at $index is $value")
}

3.5.4 while循环

package com.easy.kotlin

/**
* Created by jack on 2017/6/9.
*/

fun main(args: Array<String>) {
var x = 10
while (x > 0) {
x--
println(x)
}

var y = 10
do {
y = y + 1
println(y)
} while (y < 20) // y的作用域包含此处
}

3.5.5 break 和 continue

break

continue

1.break

false

break

break

fun breakDemo_1() {
for (i in 1..10) {
println(i)
if (i % 2 == 0) {
break
}
} // break to here
}

@Test
fun testBreakDemo_1(){
breakDemo_1()
}

1
2

2.continue

continue

break

fun continueDemo() {
for (i in 1..10) {
if (i % 2 == 0) {
continue
}
println(i)
}
}

@Test
fun testContinueDemo() {
continueDemo()
}

1
3
5
7
9

3.5.6 return返回

return

fun sum(a: Int,b: Int): Int{
return a+b
}

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

=

>>> fun sum(a: Int,b: Int) = a + b
>>> fun max(a: Int, b: Int) = if (a > b) a else b

>>> sum(1,10)
11

>>> max(1,2)
2

>>> val sum=fun(a:Int, b:Int) = a+b
>>> sum
(kotlin.Int, kotlin.Int) -> kotlin.Int
>>> sum(1,1)
2

>>> val sumf = fun(a:Int, b:Int) = {a+b}
>>> sumf
(kotlin.Int, kotlin.Int) -> () -> kotlin.Int
>>> sumf(1,1)
() -> kotlin.Int
>>> sumf(1,1).invoke()
2

{}

>>> fun sumf(a:Int,b:Int) = {a+b}
>>> sumf(1,1)
() -> kotlin.Int
>>> sumf(1,1).invoke
error: function invocation 'invoke()' expected
sumf(1,1).invoke
^
>>> sumf(1,1).invoke()
2
>>> fun maxf(a:Int, b:Int) = {if(a>b) a else b}
>>> maxf(1,2)
() -> kotlin.Int
>>> maxf(1,2).invoke()
2

sumf

maxf

() -> kotlin.Int
() -> kotlin.Int

{}

scala> def maxf(x:Int, y:Int) = { if(x>y) x else y }
maxf: (x: Int, y: Int)Int

scala> def maxv(x:Int, y:Int) = if(x>y) x else y
maxv: (x: Int, y: Int)Int

scala> maxf(1,2)
res4: Int = 2

scala> maxv(1,2)
res6: Int = 2

maxf: (x: Int, y: Int)Int

maxv: (x: Int, y: Int)Int

invoke()

()

return

fun returnDemo_1() {
println(" START " + ::returnDemo_1.name)
val intArray = intArrayOf(1, 2, 3, 4, 5)
intArray.forEach {
if (it == 3) return
println(it)
}
println(" END " + ::returnDemo_2.name)
}

//1
//2

fun returnDemo_2() {
println(" START " + ::returnDemo_2.name)
val intArray = intArrayOf(1, 2, 3, 4, 5)
intArray.forEach(fun(a: Int) {
if (a == 3) return
println(a)
})
println(" END " + ::returnDemo_2.name)
}

//1
//2
//4
//5

returnDemo_1

break

1
2

returnDemo_2

continue

1
24
5

returnDemo_2

return

@Label

3.5.7 标签（label）

@

abc@

jarOfLove@

return

break

continue

returnDemo_2()

fun returnDemo_3() {
println(" START " + ::returnDemo_3.name)
val intArray = intArrayOf(1, 2, 3, 4, 5)
intArray.forEach here@ {
if (it == 3) return@here // 指令跳转到 lambda 表达式标签 here@ 处。继续下一个it=4的遍历循环
println(it)
}
println(" END " + ::returnDemo_3.name)
}

//1
//2
//4
//5

here@

return@here

fun returnDemo_4() {
println(" START " + ::returnDemo_4.name)
val intArray = intArrayOf(1, 2, 3, 4, 5)
intArray.forEach {
if (it == 3) return@forEach // 从 lambda 表达式 @forEach 中返回。
println(it)
}

println(" END " + ::returnDemo_4.name)
}

return@forEach

fun breakDemo_1() {
println("---------------  breakDemo_1 ---------------")
for (outer in 1..5) {
println("outer=" + outer)
for (inner in 1..10) {
println("inner=" + inner)
if (inner % 2 == 0) {
break
}
}
}
}

---------------  breakDemo_1 ---------------
outer=1
inner=1
inner=2
outer=2
inner=1
inner=2
outer=3
inner=1
inner=2
outer=4
inner=1
inner=2
outer=5
inner=1
inner=2

fun breakDemo_2() {
println("---------------  breakDemo_2 ---------------")
outer@ for (outer in 1..5)
for (inner in 1..10) {
println("inner=" + inner)
println("outer=" + outer)
if (inner % 2 == 0) {
break@outer
}
}
}

---------------  breakDemo_2 ---------------
inner=1
outer=1
inner=2
outer=1

breakDemo_1()

fun breakDemo_3() {
println("---------------  breakDemo_3 ---------------")
for (outer in 1..5)
inner@ for (inner in 1..10) {
println("inner=" + inner)
println("outer=" + outer)
if (inner % 2 == 0) {
break@inner
}
}
}

3.5.8 throw表达式

void

>>> Nothing::class
class java.lang.Void

>>> fun fail(msg:String):Nothing{ throw IllegalArgumentException(msg) }
>>> fail("XXXX")
java.lang.IllegalArgumentException: XXXX
at Line57.fail(Unknown Source)

Nothing

>>> val ex = throw Exception("YYYYYYYY")
error: 'Nothing' property type needs to be specified explicitly
val ex = throw Exception("YYYYYYYY")
^

>>> val ex:Nothing = throw Exception("YYYYYYYY")
java.lang.Exception: YYYYYYYY

>>> println(ex)
error: overload resolution ambiguity:
@InlineOnly public inline fun println(message: Any?): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: Boolean): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: Byte): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: Char): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: CharArray): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: Double): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: Float): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: Int): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: Long): Unit defined in kotlin.io
@InlineOnly public inline fun println(message: Short): Unit defined in kotlin.io
println(ex)
^

>>> ex
exception: org.jetbrains.kotlin.codegen.CompilationException: Back-end (JVM) Internal error: Unregistered script: class Line62
Cause: Unregistered script: class Line62
File being compiled and position: (1,1) in /line64.kts
PsiElement: ex
The root cause was thrown at: ScriptContext.java:86
...

3.6 代码注释

// 这是一个行注释

/* 这是一个多行的
块注释。 */

/**
* hhhh
* /**
*  fff
*  /**
*    ggggg
*  */
* */
*
* abc
*
*/
fun main(args:Array<String>){
val f = Functions()
println(f.fvoid1())
println(f.fvoid2())
println(f.sum1(1,1))
println(f.sum2(1,1))
}

3.7 语法与标识符

3.7.1 修饰符

/**
## Modifiers
*/

modifiers
: (modifier | annotations)*
;

typeModifiers
: (suspendModifier | annotations)*
;

modifier
: classModifier
: accessModifier
: varianceAnnotation
: memberModifier
: parameterModifier
: typeParameterModifier
: functionModifier
: propertyModifier
;

classModifier 类修饰符
: "abstract" 抽象类
: "final" 不可被继承final类
: "enum" 枚举类
: "open" 可继承open类
: "annotation" 注解类
: "sealed" 密封类
: "data" 数据类
;

memberModifier
: "override" 重写函数
: "open" 可被重写
: "final" 不可被重写
: "abstract" 抽象函数
: "lateinit" 后期初始化
;

accessModifier 访问权限控制, 默认是public
: "private"
: "protected"
: "public"
: "internal"  整个模块内（模块(module)是指一起编译的一组 Kotlin 源代码文件: 例如，一个 IntelliJ IDEA 模块，一个 Maven 工程, 或 Gradle 工程，通过 Ant 任务的一次调用编译的一组文件等）可访问
;

varianceAnnotation 泛型可变性
: "in"
: "out"
;

parameterModifier
: "noinline"
: "crossinline"
: "vararg" 变长参数
;

typeParameterModifier
: "reified"
;

functionModifier
: "tailrec" 尾递归
: "operator"
: "infix"
: "inline"
: "external"
: suspendModifier
;

propertyModifier
: "const"
;

suspendModifier
: "suspend"
;

KtModifierKeywordToken[] MODIFIER_KEYWORDS_ARRAY =
new KtModifierKeywordToken[] {
ABSTRACT_KEYWORD, ENUM_KEYWORD, OPEN_KEYWORD, INNER_KEYWORD, OVERRIDE_KEYWORD, PRIVATE_KEYWORD,
PUBLIC_KEYWORD, INTERNAL_KEYWORD, PROTECTED_KEYWORD, OUT_KEYWORD, IN_KEYWORD, FINAL_KEYWORD, VARARG_KEYWORD,
REIFIED_KEYWORD, COMPANION_KEYWORD, SEALED_KEYWORD, LATEINIT_KEYWORD,
DATA_KEYWORD, INLINE_KEYWORD, NOINLINE_KEYWORD, TAILREC_KEYWORD, EXTERNAL_KEYWORD, ANNOTATION_KEYWORD, CROSSINLINE_KEYWORD,
CONST_KEYWORD, OPERATOR_KEYWORD, INFIX_KEYWORD, SUSPEND_KEYWORD, HEADER_KEYWORD, IMPL_KEYWORD
};

TokenSet MODIFIER_KEYWORDS = TokenSet.create(MODIFIER_KEYWORDS_ARRAY);

TokenSet TYPE_MODIFIER_KEYWORDS = TokenSet.create(SUSPEND_KEYWORD);
TokenSet TYPE_ARGUMENT_MODIFIER_KEYWORDS = TokenSet.create(IN_KEYWORD, OUT_KEYWORD);
TokenSet RESERVED_VALUE_PARAMETER_MODIFIER_KEYWORDS = TokenSet.create(OUT_KEYWORD, VARARG_KEYWORD);

TokenSet VISIBILITY_MODIFIERS = TokenSet.create(PRIVATE_KEYWORD, PUBLIC_KEYWORD, INTERNAL_KEYWORD, PROTECTED_KEYWORD);

3.7.2 关键字(保留字)

TokenSet KEYWORDS = TokenSet.create(PACKAGE_KEYWORD, AS_KEYWORD, TYPE_ALIAS_KEYWORD, CLASS_KEYWORD, INTERFACE_KEYWORD,
THIS_KEYWORD, SUPER_KEYWORD, VAL_KEYWORD, VAR_KEYWORD, FUN_KEYWORD, FOR_KEYWORD,
NULL_KEYWORD,
TRUE_KEYWORD, FALSE_KEYWORD, IS_KEYWORD,
IN_KEYWORD, THROW_KEYWORD, RETURN_KEYWORD, BREAK_KEYWORD, CONTINUE_KEYWORD, OBJECT_KEYWORD, IF_KEYWORD,
ELSE_KEYWORD, WHILE_KEYWORD, DO_KEYWORD, TRY_KEYWORD, WHEN_KEYWORD,
NOT_IN, NOT_IS, AS_SAFE,
TYPEOF_KEYWORD
);

TokenSet SOFT_KEYWORDS = TokenSet.create(FILE_KEYWORD, IMPORT_KEYWORD, WHERE_KEYWORD, BY_KEYWORD, GET_KEYWORD,
SET_KEYWORD, ABSTRACT_KEYWORD, ENUM_KEYWORD, OPEN_KEYWORD, INNER_KEYWORD,
OVERRIDE_KEYWORD, PRIVATE_KEYWORD, PUBLIC_KEYWORD, INTERNAL_KEYWORD, PROTECTED_KEYWORD,
CATCH_KEYWORD, FINALLY_KEYWORD, OUT_KEYWORD, FINAL_KEYWORD, VARARG_KEYWORD, REIFIED_KEYWORD,
DYNAMIC_KEYWORD, COMPANION_KEYWORD, CONSTRUCTOR_KEYWORD, INIT_KEYWORD, SEALED_KEYWORD,
FIELD_KEYWORD, PROPERTY_KEYWORD, RECEIVER_KEYWORD, PARAM_KEYWORD, SETPARAM_KEYWORD,
DELEGATE_KEYWORD,
LATEINIT_KEYWORD,
DATA_KEYWORD, INLINE_KEYWORD, NOINLINE_KEYWORD, TAILREC_KEYWORD, EXTERNAL_KEYWORD,
ANNOTATION_KEYWORD, CROSSINLINE_KEYWORD, CONST_KEYWORD, OPERATOR_KEYWORD, INFIX_KEYWORD,
SUSPEND_KEYWORD, HEADER_KEYWORD, IMPL_KEYWORD
);

KtKeywordToken PACKAGE_KEYWORD          = KtKeywordToken.keyword("package");
KtKeywordToken AS_KEYWORD               = KtKeywordToken.keyword("as");
KtKeywordToken TYPE_ALIAS_KEYWORD       = KtKeywordToken.keyword("typealias");
KtKeywordToken CLASS_KEYWORD            = KtKeywordToken.keyword("class");
KtKeywordToken THIS_KEYWORD             = KtKeywordToken.keyword("this");
KtKeywordToken SUPER_KEYWORD            = KtKeywordToken.keyword("super");
KtKeywordToken VAL_KEYWORD              = KtKeywordToken.keyword("val");
KtKeywordToken VAR_KEYWORD              = KtKeywordToken.keyword("var");
KtKeywordToken FUN_KEYWORD              = KtKeywordToken.keyword("fun");
KtKeywordToken FOR_KEYWORD              = KtKeywordToken.keyword("for");
KtKeywordToken NULL_KEYWORD             = KtKeywordToken.keyword("null");
KtKeywordToken TRUE_KEYWORD             = KtKeywordToken.keyword("true");
KtKeywordToken FALSE_KEYWORD            = KtKeywordToken.keyword("false");
KtKeywordToken IS_KEYWORD               = KtKeywordToken.keyword("is");
KtModifierKeywordToken IN_KEYWORD       = KtModifierKeywordToken.keywordModifier("in");
KtKeywordToken THROW_KEYWORD            = KtKeywordToken.keyword("throw");
KtKeywordToken RETURN_KEYWORD           = KtKeywordToken.keyword("return");
KtKeywordToken BREAK_KEYWORD            = KtKeywordToken.keyword("break");
KtKeywordToken CONTINUE_KEYWORD         = KtKeywordToken.keyword("continue");
KtKeywordToken OBJECT_KEYWORD           = KtKeywordToken.keyword("object");
KtKeywordToken IF_KEYWORD               = KtKeywordToken.keyword("if");
KtKeywordToken TRY_KEYWORD              = KtKeywordToken.keyword("try");
KtKeywordToken ELSE_KEYWORD             = KtKeywordToken.keyword("else");
KtKeywordToken WHILE_KEYWORD            = KtKeywordToken.keyword("while");
KtKeywordToken DO_KEYWORD               = KtKeywordToken.keyword("do");
KtKeywordToken WHEN_KEYWORD             = KtKeywordToken.keyword("when");
KtKeywordToken INTERFACE_KEYWORD        = KtKeywordToken.keyword("interface");

// Reserved for future use:
KtKeywordToken TYPEOF_KEYWORD           = KtKeywordToken.keyword("typeof");
...
KtKeywordToken FILE_KEYWORD    = KtKeywordToken.softKeyword("file");
KtKeywordToken FIELD_KEYWORD     = KtKeywordToken.softKeyword("field");
KtKeywordToken PROPERTY_KEYWORD     = KtKeywordToken.softKeyword("property");
KtKeywordToken RECEIVER_KEYWORD     = KtKeywordToken.softKeyword("receiver");
KtKeywordToken PARAM_KEYWORD     = KtKeywordToken.softKeyword("param");
KtKeywordToken SETPARAM_KEYWORD  = KtKeywordToken.softKeyword("setparam");
KtKeywordToken DELEGATE_KEYWORD  = KtKeywordToken.softKeyword("delegate");
KtKeywordToken IMPORT_KEYWORD    = KtKeywordToken.softKeyword("import");
KtKeywordToken WHERE_KEYWORD     = KtKeywordToken.softKeyword("where");
KtKeywordToken BY_KEYWORD        = KtKeywordToken.softKeyword("by");
KtKeywordToken GET_KEYWORD       = KtKeywordToken.softKeyword("get");
KtKeywordToken SET_KEYWORD       = KtKeywordToken.softKeyword("set");
KtKeywordToken CONSTRUCTOR_KEYWORD = KtKeywordToken.softKeyword("constructor");
KtKeywordToken INIT_KEYWORD        = KtKeywordToken.softKeyword("init");

KtModifierKeywordToken ABSTRACT_KEYWORD  = KtModifierKeywordToken.softKeywordModifier("abstract");
KtModifierKeywordToken ENUM_KEYWORD      = KtModifierKeywordToken.softKeywordModifier("enum");
KtModifierKeywordToken OPEN_KEYWORD      = KtModifierKeywordToken.softKeywordModifier("open");
KtModifierKeywordToken INNER_KEYWORD     = KtModifierKeywordToken.softKeywordModifier("inner");
KtModifierKeywordToken OVERRIDE_KEYWORD  = KtModifierKeywordToken.softKeywordModifier("override");
KtModifierKeywordToken PRIVATE_KEYWORD   = KtModifierKeywordToken.softKeywordModifier("private");
KtModifierKeywordToken PUBLIC_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("public");
KtModifierKeywordToken INTERNAL_KEYWORD  = KtModifierKeywordToken.softKeywordModifier("internal");
KtModifierKeywordToken PROTECTED_KEYWORD = KtModifierKeywordToken.softKeywordModifier("protected");
KtKeywordToken CATCH_KEYWORD     = KtKeywordToken.softKeyword("catch");
KtModifierKeywordToken OUT_KEYWORD       = KtModifierKeywordToken.softKeywordModifier("out");
KtModifierKeywordToken VARARG_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("vararg");
KtModifierKeywordToken REIFIED_KEYWORD   = KtModifierKeywordToken.softKeywordModifier("reified");
KtKeywordToken DYNAMIC_KEYWORD   = KtKeywordToken.softKeyword("dynamic");
KtModifierKeywordToken COMPANION_KEYWORD = KtModifierKeywordToken.softKeywordModifier("companion");
KtModifierKeywordToken SEALED_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("sealed");

KtModifierKeywordToken DEFAULT_VISIBILITY_KEYWORD = PUBLIC_KEYWORD;

KtKeywordToken FINALLY_KEYWORD   = KtKeywordToken.softKeyword("finally");
KtModifierKeywordToken FINAL_KEYWORD     = KtModifierKeywordToken.softKeywordModifier("final");

KtModifierKeywordToken LATEINIT_KEYWORD = KtModifierKeywordToken.softKeywordModifier("lateinit");

KtModifierKeywordToken DATA_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("data");
KtModifierKeywordToken INLINE_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("inline");
KtModifierKeywordToken NOINLINE_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("noinline");
KtModifierKeywordToken TAILREC_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("tailrec");
KtModifierKeywordToken EXTERNAL_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("external");
KtModifierKeywordToken ANNOTATION_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("annotation");
KtModifierKeywordToken CROSSINLINE_KEYWORD    = KtModifierKeywordToken.softKeywordModifier("crossinline");
KtModifierKeywordToken OPERATOR_KEYWORD = KtModifierKeywordToken.softKeywordModifier("operator");
KtModifierKeywordToken INFIX_KEYWORD = KtModifierKeywordToken.softKeywordModifier("infix");

KtModifierKeywordToken CONST_KEYWORD = KtModifierKeywordToken.softKeywordModifier("const");

KtModifierKeywordToken SUSPEND_KEYWORD = KtModifierKeywordToken.softKeywordModifier("suspend");

KtModifierKeywordToken HEADER_KEYWORD = KtModifierKeywordToken.softKeywordModifier("header");
KtModifierKeywordToken IMPL_KEYWORD = KtModifierKeywordToken.softKeywordModifier("impl");

this

关键字

this

this

return this

class ThisDemo {
val thisis = "THIS IS"

fun whatIsThis(): ThisDemo {
println(this.thisis) //引用变量
this.howIsThis()// 引用成员函数
return this // 返回此类的引用
}

fun howIsThis(){
println("HOW IS THIS ?")
}
}

@Test
fun testThisDemo(){
val demo = ThisDemo()
println(demo.whatIsThis())
}

THIS IS
HOW IS THIS ?
com.easy.kotlin.ThisDemo@475232fc

>>> val sum = fun Int.(x:Int):Int = this + x
>>> sum
kotlin.Int.(kotlin.Int) -> kotlin.Int
>>> 1.sum(1)
2
>>> val concat = fun String.(x:Any) = this + x
>>> "abc".concat(123)
abc123
>>> "abc".concat(true)
abctrue

class Outer {
val oh = "Oh!"

inner class Inner {

fun m() {
val outer = this@Outer
val inner = this@Inner
val pthis = this
println("outer=" + outer)
println("inner=" + inner)
println("pthis=" + pthis)
println(this@Outer.oh)

val fun1 = hello@ fun String.() {
val d1 = this // fun1 的接收者
println("d1" + d1)
}

val fun2 = { s: String ->
val d2 = this
println("d2=" + d2)
}

"abc".fun1()

fun2

}
}

}

@Test
fun testThisKeyWord() {
val outer = Outer()
outer.Inner().m()
}

outer=com.easy.kotlin.Outer@5114e183
inner=com.easy.kotlin.Outer$Inner@5aa8ac7f
pthis=com.easy.kotlin.Outer$Inner@5aa8ac7f
Oh!
d1abc

super 关键字

open class Father {
open val firstName = "Chen"
open val lastName = "Jason"

fun ff() {
println("FFF")
}
}

class Son : Father {
override var firstName = super.firstName
override var lastName = "Jack"

constructor(lastName: String) {
this.lastName = lastName
}

fun love() {
super.ff() // 调用父类方法
println(super.firstName + " " + super.lastName + " Love " + this.firstName + " " + this.lastName)
}
}

@Test
fun testSuperKeyWord() {
val son = Son("Harry")
son.love()
}

FFF
Chen Jason Love Chen Harry

3.7.3 操作符和操作符的重载

+

*

KtSingleValueToken LBRACKET    = new KtSingleValueToken("LBRACKET", "[");
KtSingleValueToken RBRACKET    = new KtSingleValueToken("RBRACKET", "]");
KtSingleValueToken LBRACE      = new KtSingleValueToken("LBRACE", "{");
KtSingleValueToken RBRACE      = new KtSingleValueToken("RBRACE", "}");
KtSingleValueToken LPAR        = new KtSingleValueToken("LPAR", "(");
KtSingleValueToken RPAR        = new KtSingleValueToken("RPAR", ")");
KtSingleValueToken DOT         = new KtSingleValueToken("DOT", ".");
KtSingleValueToken PLUSPLUS    = new KtSingleValueToken("PLUSPLUS", "++");
KtSingleValueToken MINUSMINUS  = new KtSingleValueToken("MINUSMINUS", "--");
KtSingleValueToken MUL         = new KtSingleValueToken("MUL", "*");
KtSingleValueToken PLUS        = new KtSingleValueToken("PLUS", "+");
KtSingleValueToken MINUS       = new KtSingleValueToken("MINUS", "-");
KtSingleValueToken EXCL        = new KtSingleValueToken("EXCL", "!");
KtSingleValueToken DIV         = new KtSingleValueToken("DIV", "/");
KtSingleValueToken PERC        = new KtSingleValueToken("PERC", "%");
KtSingleValueToken LT          = new KtSingleValueToken("LT", "<");
KtSingleValueToken GT          = new KtSingleValueToken("GT", ">");
KtSingleValueToken LTEQ        = new KtSingleValueToken("LTEQ", "<=");
KtSingleValueToken GTEQ        = new KtSingleValueToken("GTEQ", ">=");
KtSingleValueToken EQEQEQ      = new KtSingleValueToken("EQEQEQ", "===");
KtSingleValueToken ARROW       = new KtSingleValueToken("ARROW", "->");
KtSingleValueToken DOUBLE_ARROW       = new KtSingleValueToken("DOUBLE_ARROW", "=>");
KtSingleValueToken EXCLEQEQEQ  = new KtSingleValueToken("EXCLEQEQEQ", "!==");
KtSingleValueToken EQEQ        = new KtSingleValueToken("EQEQ", "==");
KtSingleValueToken EXCLEQ      = new KtSingleValueToken("EXCLEQ", "!=");
KtSingleValueToken EXCLEXCL    = new KtSingleValueToken("EXCLEXCL", "!!");
KtSingleValueToken ANDAND      = new KtSingleValueToken("ANDAND", "&&");
KtSingleValueToken OROR        = new KtSingleValueToken("OROR", "||");
KtSingleValueToken SAFE_ACCESS = new KtSingleValueToken("SAFE_ACCESS", "?.");
KtSingleValueToken ELVIS       = new KtSingleValueToken("ELVIS", "?:");
KtSingleValueToken QUEST       = new KtSingleValueToken("QUEST", "?");
KtSingleValueToken COLONCOLON  = new KtSingleValueToken("COLONCOLON", "::");
KtSingleValueToken COLON       = new KtSingleValueToken("COLON", ":");
KtSingleValueToken SEMICOLON   = new KtSingleValueToken("SEMICOLON", ";");
KtSingleValueToken DOUBLE_SEMICOLON   = new KtSingleValueToken("DOUBLE_SEMICOLON", ";;");
KtSingleValueToken RANGE       = new KtSingleValueToken("RANGE", "..");
KtSingleValueToken EQ          = new KtSingleValueToken("EQ", "=");
KtSingleValueToken MULTEQ      = new KtSingleValueToken("MULTEQ", "*=");
KtSingleValueToken DIVEQ       = new KtSingleValueToken("DIVEQ", "/=");
KtSingleValueToken PERCEQ      = new KtSingleValueToken("PERCEQ", "%=");
KtSingleValueToken PLUSEQ      = new KtSingleValueToken("PLUSEQ", "+=");
KtSingleValueToken MINUSEQ     = new KtSingleValueToken("MINUSEQ", "-=");
KtKeywordToken NOT_IN      = KtKeywordToken.keyword("NOT_IN", "!in");
KtKeywordToken NOT_IS      = KtKeywordToken.keyword("NOT_IS", "!is");
KtSingleValueToken HASH        = new KtSingleValueToken("HASH", "#");
KtSingleValueToken AT          = new KtSingleValueToken("AT", "@");

KtSingleValueToken COMMA       = new KtSingleValueToken("COMMA", ",");

3.7.4 操作符优先级（Precedence)

++

--

.

?.

?

-

+

++

--

!

labelDefinition

@

:

as

as?

*

/

%

+

-

..

Int

infix fun Int.shl(x: Int): Int {...}

1 shl 2

1.shl(2)

?:

in

!in

is

!is

<

>

<=

>=

==

\!==

&&

ll

=

+=

-=

*=

/=

%=

ll

||

public class Int private constructor() : Number(), Comparable<Int> {
...

/**
* Compares this value with the specified value for order.
* Returns zero if this value is equal to the specified other value, a negative number if it's less than other,
* or a positive number if it's greater than other.
*/
public operator fun compareTo(other: Byte): Int

/**
* Compares this value with the specified value for order.
* Returns zero if this value is equal to the specified other value, a negative number if it's less than other,
* or a positive number if it's greater than other.
*/
public operator fun compareTo(other: Short): Int

/**
* Compares this value with the specified value for order.
* Returns zero if this value is equal to the specified other value, a negative number if it's less than other,
* or a positive number if it's greater than other.
*/
public override operator fun compareTo(other: Int): Int

/**
* Compares this value with the specified value for order.
* Returns zero if this value is equal to the specified other value, a negative number if it's less than other,
* or a positive number if it's greater than other.
*/
public operator fun compareTo(other: Long): Int

/**
* Compares this value with the specified value for order.
* Returns zero if this value is equal to the specified other value, a negative number if it's less than other,
* or a positive number if it's greater than other.
*/
public operator fun compareTo(other: Float): Int

/**
* Compares this value with the specified value for order.
* Returns zero if this value is equal to the specified other value, a negative number if it's less than other,
* or a positive number if it's greater than other.
*/
public operator fun compareTo(other: Double): Int

/** Adds the other value to this value. */
public operator fun plus(other: Byte): Int
/** Adds the other value to this value. */
public operator fun plus(other: Short): Int
/** Adds the other value to this value. */
public operator fun plus(other: Int): Int
/** Adds the other value to this value. */
public operator fun plus(other: Long): Long
/** Adds the other value to this value. */
public operator fun plus(other: Float): Float
/** Adds the other value to this value. */
public operator fun plus(other: Double): Double

/** Subtracts the other value from this value. */
public operator fun minus(other: Byte): Int
/** Subtracts the other value from this value. */
public operator fun minus(other: Short): Int
/** Subtracts the other value from this value. */
public operator fun minus(other: Int): Int
/** Subtracts the other value from this value. */
public operator fun minus(other: Long): Long
/** Subtracts the other value from this value. */
public operator fun minus(other: Float): Float
/** Subtracts the other value from this value. */
public operator fun minus(other: Double): Double

/** Multiplies this value by the other value. */
public operator fun times(other: Byte): Int
/** Multiplies this value by the other value. */
public operator fun times(other: Short): Int
/** Multiplies this value by the other value. */
public operator fun times(other: Int): Int
/** Multiplies this value by the other value. */
public operator fun times(other: Long): Long
/** Multiplies this value by the other value. */
public operator fun times(other: Float): Float
/** Multiplies this value by the other value. */
public operator fun times(other: Double): Double

/** Divides this value by the other value. */
public operator fun div(other: Byte): Int
/** Divides this value by the other value. */
public operator fun div(other: Short): Int
/** Divides this value by the other value. */
public operator fun div(other: Int): Int
/** Divides this value by the other value. */
public operator fun div(other: Long): Long
/** Divides this value by the other value. */
public operator fun div(other: Float): Float
/** Divides this value by the other value. */
public operator fun div(other: Double): Double

/** Calculates the remainder of dividing this value by the other value. */
@Deprecated("Use rem(other) instead", ReplaceWith("rem(other)"), DeprecationLevel.WARNING)
public operator fun mod(other: Byte): Int
/** Calculates the remainder of dividing this value by the other value. */
@Deprecated("Use rem(other) instead", ReplaceWith("rem(other)"), DeprecationLevel.WARNING)
public operator fun mod(other: Short): Int
/** Calculates the remainder of dividing this value by the other value. */
@Deprecated("Use rem(other) instead", ReplaceWith("rem(other)"), DeprecationLevel.WARNING)
public operator fun mod(other: Int): Int
/** Calculates the remainder of dividing this value by the other value. */
@Deprecated("Use rem(other) instead", ReplaceWith("rem(other)"), DeprecationLevel.WARNING)
public operator fun mod(other: Long): Long
/** Calculates the remainder of dividing this value by the other value. */
@Deprecated("Use rem(other) instead", ReplaceWith("rem(other)"), DeprecationLevel.WARNING)
public operator fun mod(other: Float): Float
/** Calculates the remainder of dividing this value by the other value. */
@Deprecated("Use rem(other) instead", ReplaceWith("rem(other)"), DeprecationLevel.WARNING)
public operator fun mod(other: Double): Double

/** Calculates the remainder of dividing this value by the other value. */
@SinceKotlin("1.1")
public operator fun rem(other: Byte): Int
/** Calculates the remainder of dividing this value by the other value. */
@SinceKotlin("1.1")
public operator fun rem(other: Short): Int
/** Calculates the remainder of dividing this value by the other value. */
@SinceKotlin("1.1")
public operator fun rem(other: Int): Int
/** Calculates the remainder of dividing this value by the other value. */
@SinceKotlin("1.1")
public operator fun rem(other: Long): Long
/** Calculates the remainder of dividing this value by the other value. */
@SinceKotlin("1.1")
public operator fun rem(other: Float): Float
/** Calculates the remainder of dividing this value by the other value. */
@SinceKotlin("1.1")
public operator fun rem(other: Double): Double

/** Increments this value. */
public operator fun inc(): Int
/** Decrements this value. */
public operator fun dec(): Int
/** Returns this value. */
public operator fun unaryPlus(): Int
/** Returns the negative of this value. */
public operator fun unaryMinus(): Int

/** Creates a range from this value to the specified [other] value. */
public operator fun rangeTo(other: Byte): IntRange
/** Creates a range from this value to the specified [other] value. */
public operator fun rangeTo(other: Short): IntRange
/** Creates a range from this value to the specified [other] value. */
public operator fun rangeTo(other: Int): IntRange
/** Creates a range from this value to the specified [other] value. */
public operator fun rangeTo(other: Long): LongRange

/** Shifts this value left by [bits]. */
public infix fun shl(bitCount: Int): Int
/** Shifts this value right by [bits], filling the leftmost bits with copies of the sign bit. */
public infix fun shr(bitCount: Int): Int
/** Shifts this value right by [bits], filling the leftmost bits with zeros. */
public infix fun ushr(bitCount: Int): Int
/** Performs a bitwise AND operation between the two values. */
public infix fun and(other: Int): Int
/** Performs a bitwise OR operation between the two values. */
public infix fun or(other: Int): Int
/** Performs a bitwise XOR operation between the two values. */
public infix fun xor(other: Int): Int
/** Inverts the bits in this value. */
public fun inv(): Int

public override fun toByte(): Byte
public override fun toChar(): Char
public override fun toShort(): Short
public override fun toInt(): Int
public override fun toLong(): Long
public override fun toFloat(): Float
public override fun toDouble(): Double
}

operator

infix

3.7.5 一元操作符（unary operation）

前缀操作符

+a

a.unaryPlus()

-a

a.unaryMinus()

!a

a.not()

+a

a

T

T

operator

unaryPlus（）

R

+a

R

package com.easy.kotlin

/**
* Created by jack on 2017/6/10.
*/

class OperatorDemo {

}

data class Point(val x: Int, val y: Int)

operator fun Point.unaryMinus() = Point(-x, -y)

package com.easy.kotlin

import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

/**
* Created by jack on 2017/6/10.
*/
@RunWith(JUnit4::class)
class OperatorDemoTest {

@Test
fun testPointUnaryMinus() {
val p = Point(1, 1)
val np = -p
println(np) //Point(x=-1, y=-1)
}
}

递增和递减

a++

a.inc()

a

a--

a.dec()

a

++a

a.inc()

a+1

--a

a.dec()

a-1

inc()

dec()

++

--

a++

a

T

T

operator

inc()

T

a

a_

a.inc()

a

a_

a--

++a

--a

a.inc()

a

a

a+1

--a

3.7.6 二元操作符

算术运算符

a + b

a.plus(b)

a - b

a.minus(b)

a * b

a.times(b)

a / b

a.div(b)

a % b

a.rem(b)

a.mod(b)

a..b

a.rangeTo(b)

>>> val a=10
>>> val b=3
>>> a+b
13
>>> a-b
7
>>> a/b
3
>>> a%b
1
>>> a..b
10..3
>>> b..a
3..10

字符串的

+

运算符重载

>>> ""+1
1
>>> 1+""
error: none of the following functions can be called with the arguments supplied:
public final operator fun plus(other: Byte): Int defined in kotlin.Int
public final operator fun plus(other: Double): Double defined in kotlin.Int
public final operator fun plus(other: Float): Float defined in kotlin.Int
public final operator fun plus(other: Int): Int defined in kotlin.Int
public final operator fun plus(other: Long): Long defined in kotlin.Int
public final operator fun plus(other: Short): Int defined in kotlin.Int
1+""
^

1+""

toString

>>> 1.toString()+""
1

自定义重载的

+

运算符

+

data class Counter(var index: Int)

operator fun Counter.plus(increment: Int): Counter {
return Counter(index + increment)
}

package com.easy.kotlin

import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

/**
* Created by jack on 2017/6/10.
*/
@RunWith(JUnit4::class)
class OperatorDemoTest
@Test
fun testCounterIndexPlus() {
val c = Counter(1)
val cplus = c + 10
println(cplus) //Counter(index=11)
}
}

in

操作符

a in b

b.contains(a)

a !in b

!b.contains(a)

索引访问操作符

a[i]

a.get(i)

a[i] = b

a.set(i, b)

get

set

调用操作符

a()

a.invoke()

a(i)

a.invoke(i)

invoke

计算并赋值

a += b

a.plusAssign(b)

a -= b

a.minusAssign(b)

a *= b

a.timesAssign(b)

a /= b

a.divAssign(b)

a %= b

a.modAssign(b)

a += b

a = a + b

a + b

a

相等与不等操作符

===

!==

==

!=

equals()

a == b

a?.equals(b) ?: (b === null)

a != b

!(a?.equals(b) ?: (b === null))

==

null

equals(Any?)

a === null

b === null

a == null

a=== null

===

!==

Elvis 操作符

?:

y = x?:0

val y = if(x!==null) x else 0

null

?:

true?1:0

if(true) 1 else 0

String name = "Elvis Presley";
String displayName = (name != null) ? name : "Unknown";

String name = "Elvis Presley";
String displayName = name?:"Unknown"

NullPointerException

>>> val x = null
>>> val y = x?:0>>> y
0
>>> val x = false
>>> val y = x?:0>>> y
false
>>> val x = ""
>>> val y = x?:0>>> y

>>> val x = "abc"
>>> val y = x?:0>>> y
abc

比较操作符

a > b

a.compareTo(b) > 0

a < b

a.compareTo(b) < 0

a >= b

a.compareTo(b) >= 0

a <= b

a.compareTo(b) <= 0

compareTo

Int

用infix函数自定义中缀操作符

data class Person(val name: String, val age: Int)

infix fun Person.grow(years: Int): Person {
return Person(name, age + years)
}

package com.easy.kotlin

import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

/**
* Created by jack on 2017/6/11.
*/
@RunWith(JUnit4::class)
class InfixFunctionDemoTest {

@Test fun testInfixFuntion() {
val person = Person("Jack", 20)

println(person.grow(2))

println(person grow 2)
}
}

Person(name=Jack, age=22)
Person(name=Jack, age=22)

3.8 函数扩展和属性扩展(Extensions)

package com.easy.kotlin

/**
* Created by jack on 2017/6/11.
*/

val <T> List<T>.lastIndex: Int get() = size - 1

fun String.notEmpty(): Boolean {
return !this.isEmpty()
}

package com.example.usage

import foo.bar.goo // 导入所有名为“goo”的扩展
// 或者
import foo.bar.*   // 从“foo.bar”导入一切

fun usage(baz: Baz) {
baz.goo()
}

3.8.1 扩展函数

>>> !"123".isEmpty()
true

String

notEmpty()

>>> fun String.notEmpty():Boolean{
... return !this.isEmpty()
... }

>>> "".notEmpty()
false

>>> "123".notEmpty()
true

MutableList<Int>

swap

fun MutableList<Int>.swap(index1: Int, index2: Int) {
val tmp = this[index1] // this对应该列表
this[index1] = this[index2]
this[index2] = tmp
}

this

.

MutableList<Int>

MutableList<T>

fun <T> MutableList<T>.mswap(index1: Int, index2: Int) {
val tmp = this[index1] // “this”对应该列表
this[index1] = this[index2]
this[index2] = tmp
}

package com.easy.kotlin

/**
* Created by jack on 2017/6/11.
*/

val <T> List<T>.lastIndex: Int get() = size - 1

fun String.notEmpty(): Boolean {
return !this.isEmpty()
}fun MutableList<Int>.swap(index1: Int, index2: Int) {
val tmp = this[index1] // this对应该列表m
this[index1] = this[index2]
this[index2] = tmp
}

fun <T> MutableList<T>.mswap(index1: Int, index2: Int) {
val tmp = this[index1] // “this”对应该列表
this[index1] = this[index2]
this[index2] = tmp
}

class ExtensionsDemo {

fun useExtensions() {
val a = "abc"
println(a.notEmpty())//true

val mList = mutableListOf<Int>(1, 2, 3, 4, 5)
println("Before Swap:")
println(mList)//[1, 2, 3, 4, 5]
mList.swap(0, mList.size - 1)
println("After Swap:")
println(mList)//[5, 2, 3, 4, 1]

val mmList = mutableListOf<String>("a12", "b34", "c56", "d78")
println("Before Swap:")
println(mmList)//[a12, b34, c56, d78]
mmList.mswap(1, 2)
println("After Swap:")
println(mmList)//[a12, c56, b34, d78]

val mmmList = mutableListOf<Int>(100, 200, 300, 400, 500)
println("Before Swap:")
println(mmmList)
mmmList.mswap(0, mmmList.lastIndex)
println("After Swap:")
println(mmmList)
}

class Inner {
fun useExtensions() {
val mmmList = mutableListOf<Int>(100, 200, 300, 400, 500)
println(mmmList.lastIndex)
}
}
}

package com.easy.kotlin

import org.junit.Test
import org.junit.runner.RunWith
import org.junit.runners.JUnit4

/**
* Created by jack on 2017/6/11.
*/

@RunWith(JUnit4::class)
class ExtensionsDemoTest {
@Test fun testExtensionsDemo() {
val demo = ExtensionsDemo()
demo.useExtensions()
}
}

.

3.8.2 扩展属性

val <T> List<T>.lastIndex: Int
get() = size - 1

package com.easy.kotlin

/**
* Created by jack on 2017/6/11.
*/

val <T> List<T>.lastIndex: Int get() = size - 1

com.easy.kotlin

lastIndex

3.9 空指针安全(Null-safety)

throw NullPointerException()

!!

this

null

null

null

>>> var a="abc"
>>> a=null
error: null can not be a value of a non-null type String
a=null
^

>>> var one=1
>>> one=null
error: null can not be a value of a non-null type Int
one=null
^

>>> var arrayInts = intArrayOf(1,2,3)
>>> arrayInts=null
error: null can not be a value of a non-null type IntArray
arrayInts=null
^

a

NPE

>>> val a="abc"
>>> a.length
3

?

>>> var a:String?="abc"
>>> a=null
>>> var one:Int?=1
>>> one=null
>>> var arrayInts:IntArray?=intArrayOf(1,2,3)
>>> arrayInts=null
>>> arrayInts
null

String?

na

length

>>> var na:String?="abc"
>>> na=null
>>> na.length
error: only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type String?
na.length
^

?.

!!.

>>> na?.length
null
>>> na!!.length
kotlin.KotlinNullPointerException

null

kotlin.KotlinNullPointerException

let

>>> val listWithNulls: List<String?> = listOf("A", "B",null)
>>> listWithNulls
[A, B, null]

>>> listWithNulls.forEach{
... it?.let{println(it)}
... }
A
B

参考资料