kotlin方言（对比其它语言）

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土匪猿 2018-09-09 20:36:09 博主文章分类：Android ©著作权

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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