kotlin方言（对比其它语言）

环境：
mac 安装 kotlin
sudo brew install kotlin
ide: idea
先测试java

public class allen {
public static void  main(String[] args) {
System.out.println("fuck you java");
}
}

liuhailongdeAir:src liuhailong$ ls
allen.java
liuhailongdeAir:src liuhailong$ java allen.java
错误: 找不到或无法加载主类 allen.java
liuhailongdeAir:src liuhailong$ javac allen.java
liuhailongdeAir:src liuhailong$ ls
allen.class allen.java
liuhailongdeAir:src liuhailong$ java allen.class
错误: 找不到或无法加载主类 allen.class
liuhailongdeAir:src liuhailong$ java allen.
错误: 找不到或无法加载主类 allen.
liuhailongdeAir:src liuhailong$ java allen
1d 37 1d 37 c 13 15 10 10 26 d 2f 1b 10 40 40
3t3tMTVQQcNl1Q//
liuhailongdeAir:src liuhailong$ javac allen.java
liuhailongdeAir:src liuhailong$ java allen
fuck you java
liuhailongdeAir:src liuhailong$

kotlin编译：
第一种方式： （出错）
kotlinc test.kt -include-runtime 或kotlinc test.kt -include-runtime -d allen
java TestKt

fun main(args: Array<String>) {
println("fuck you kotlin");
}

liuhailongdeAir:src liuhailong$ ls
test.kt
liuhailongdeAir:src liuhailong$ kotlin test.kt -include-runtime
error: could not find or load main class test.kt
liuhailongdeAir:src liuhailong$ kotlinc test.kt -include-runtime
liuhailongdeAir:src liuhailong$ ls
META-INF    TestKt.class    test.kt
liuhailongdeAir:src liuhailong$ javap TestKt.class
Compiled from "test.kt"
public final class TestKt {
public static final void main(java.lang.String[]);
}
liuhailongdeAir:src liuhailong$ ls
META-INF    TestKt.class    test.kt
liuhailongdeAir:src liuhailong$ ls
META-INF    TestKt.class    test.kt
liuhailongdeAir:src liuhailong$ kotlinc test.kt -include-runtime
liuhailongdeAir:src liuhailong$ ls
META-INF    TestKt.class    test.kt
liuhailongdeAir:src liuhailong$ java TestKt.class
错误: 找不到或无法加载主类 TestKt.class
liuhailongdeAir:src liuhailong$ java TestKt
Exception in thread "main" java.lang.NoClassDefFoundError: kotlin/jvm/internal/Intrinsics
at TestKt.main(test.kt)
Caused by: java.lang.ClassNotFoundException: kotlin.jvm.internal.Intrinsics
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 1 more
liuhailongdeAir:src liuhailong$ kotlinc test.kt -include-runtime
liuhailongdeAir:src liuhailong$ kotlinc test.kt -include-runtime  -d allen
liuhailongdeAir:src liuhailong$ ls
META-INF    TestKt.class    allen       test.kt
liuhailongdeAir:src liuhailong$ cd allen
liuhailongdeAir:allen liuhailong$ ls
META-INF    TestKt.class
liuhailongdeAir:allen liuhailong$ java TestKt.class
错误: 找不到或无法加载主类 TestKt.class
liuhailongdeAir:allen liuhailong$ java TestKt
Exception in thread "main" java.lang.NoClassDefFoundError: kotlin/jvm/internal/Intrinsics
at TestKt.main(test.kt)
Caused by: java.lang.ClassNotFoundException: kotlin.jvm.internal.Intrinsics
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 1 more
liuhailongdeAir:allen liuhailong$

第二种方式
kotlinc test.kt -include-runtime -d allen.jar
java -jar allen.jar

liuhailongdeAir:allen liuhailong$ kotlinc test.kt -include-runtime  -d allen.jar
error: source file or directory not found: test.kt
liuhailongdeAir:allen liuhailong$ cd ..
liuhailongdeAir:src liuhailong$ cd ..
liuhailongdeAir:testa liuhailong$ ls
out     src     testa.iml
liuhailongdeAir:testa liuhailong$ cd src/
liuhailongdeAir:src liuhailong$ kotlinc test.kt -include-runtime  -d allen.jar
liuhailongdeAir:src liuhailong$ ls
META-INF    TestKt.class    allen       allen.jar   test.kt
liuhailongdeAir:src liuhailong$ java -jar allen.jar
fuck you kotlin
liuhailongdeAir:src liuhailong$

原因是他自动生成一个类，还有很多依赖项（同时自动改名 ）
解压 jar 包

查看 class 文件

liuhailongdeAir:IdeaProjects liuhailong$ ls
testa       testjava    testkotlin
liuhailongdeAir:IdeaProjects liuhailong$ cd testa
liuhailongdeAir:testa liuhailong$ ls
out     src     testa.iml
liuhailongdeAir:testa liuhailong$ cd src/
liuhailongdeAir:src liuhailong$ ls
META-INF    allen       test.kt
TestKt.class    allen.jar
liuhailongdeAir:src liuhailong$ javap TestKt.class
Compiled from "test.kt"
public final class TestKt {
public static final void main(java.lang.String[]);
}
liuhailongdeAir:src liuhailong$

因此在 idea 中有个设置入口类名称就是填对应的名称加 Kt ，同时第一个字母要大写

方言：（pascal风格 swift 也是）
变量的类型在后面 ,可以不写类型 var 定义自动推断类型。
函数有声名，返回值类型在后面与 swift 一样但格式不一样

\\js 弱类型语言返回值自动推断
function add2(x,y)
{
sum = x + y;
return sum;
}
\\swift 强类型
func sayHello(personName: String) -> String {
let greeting = "Hello, " + personName + "!"//let常量
return greeting
}
\\kotlin
fun add(m:Int,n:Int):Int{
return m+n
}

when(switch)每个分支中自动 break 格式 为xx ->（）（ swift用关键字case 也没有 break）
when 中可能有范围用 in （swift 也可以有 ）
类
//swift

class MarksStruct {
var mark : Int
init(mark : Int) {
self.mark = mark
}
}

//java

class Person{
String name;
int age;
public void tell(){
System.out.println("姓名："+name+"   "+"年龄："+age);
}
}

//kotlin 构造函数与类型可以合到一起使用

class Customer(name: String) {
init {
logger.info("Customer initialized with value ${name}")
}
}
class allen() {}

get/set 方法
//java

public class User {
private String username;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}

}

//kotlin

class User {
val username:String
get()=allen
set(value:String)
{
allen=value
}
}

//swift

var _name:String?
var name:String?{
get{
return _name;
}
set{
_name = newValue
}
//同时有个回调 当被修改时调用
didSet
{
NSLog("已经改变的时候", []);
}
}

接口 枚举 抽象类与关键字与 java一样
继承 有点不一样 当一个类可以被 其它类继承时 这个类前面加关键字 open
kotlin 与 oc swift 一样有扩展功能
kotlin 中的泛型与 java 类似
java中的静态类成员在kotlin中用陪伴对象实现 也就是kotlin没有静态类成员
kotlin 有委托功能 类通过关键字 by 属性通过 operator
kotlin一样支持函数对象 高阶函数 装饰 闭包 lambda