kotlin 4

 static final int b=3;
 const val b=3;//只能定义在全局范围 只能修饰基本类型 必须立即用字面量初始化
 
    var x:Any=。。。
    val c=when{
        x is String -> x.length
        x==1 ->2
        else -> 20
    }

Operators

"hello"=="world"    "hello".equals("world")
    2+3
        2.plus(3)
    val list= listOf(1,2,3,4,)
    2 in list 
        list.contains(2)
    val map= mutableMapOf(
        "hello" to 2,
        "world" to 3
    )
    val  s=map["hello"]
         map.get("hello")

    map["world"]=4
    map.set("world",4)

Infix expression

	ss".ma("b")
    infix  fun<A,B> A.ma(that:B):Pair<A,B>
     = Pair(this,that) 

lambda expressions

    val lambda1={
        println("hello")
    }//lambda表达式返回类型取决于最后一句话的返回类型 可以省略return

    val lambda2:(Int)->Unit={
        print(it)
    }

    val lambda3={it:Int->
        print(it)
    }

    val lambda4:Function1<Int,Unit> ={
        println(it)
    }
    lambda1.invoke()==lambda1
    lambda4.invoke(1)===lambda4(1)

After rewriting hashcode equals members preferably with constant modifications it may cause memory leaks (there is after deposit hashmap hashset property value changes the cause can not be removed)