Kotlin for Android-Common keywords

Keywords in kotlin that are consistent with Java usage include: override, while declarations

· Open in Kotlin a class needs to be inherited by another class, you need to use the Open keyword

Open Class Openclass {}

· is judgment type

    Fun testis () {
        var a:any? = null;
        A = 3L
        if (A is int) {
            println (' A is int ')
        } else if (A is long) {
            println (' A is Long ')
        } else {
            P Rintln ("a not int or long")
        }
    }

· When the equivalent of Swith, we use when to optimize the previous code

    Fun TestWhen1 () {
        var a:any? = null;
        A = 3L when
        (a) {is
            int-> println (' A is int ') is
            Long-> println (' A is long ')
            else-> print ln ("A not int or long")
        }
    }

    Fun TestWhen2 () {
        var a = 2;
        When (a) {in
            1..5-> println (' A in 1~5 ') in the 6..10-> println
            ("A In 6~10")
            else-> println ("a > 10 ")
        }
    }

· As coercion type conversion

var Context.app:KotlinApplication get
    () {return
        ApplicationContext as Kotlinapplication
    }
    Set ( Value) {
        app = value
    }

· In expression within range,.. Represents a range

    Fun Testin () {
        var a = 3
        if (a in 1..5) {
            println (' A in 1~5 ')
        }
    }

· For basic and Java, the following code is equivalent to Fori in Java

For (i in list.indices) {
   println (List.get (i))
}

The following code corresponds to a foreach in Java

For (item in list) {
   println (item)
}

There are also foreach in the Kotlin, but not a keyword, as follows

List.foreach {
    println (it)
}

· Lateinit literally can be seen, used for deferred initialization, when a VAR cannot be null, but the initial unassigned, can be decorated with lateinit, if the first time to use the lateinit decorated variable still does not have a value, throw an exception. Lateinit can only be used to modify Var and not to modify Val.

Lateinit var age:string

· The by lazy{} is used to delay initialization of a Val, which executes the initialization code in lazy before using the constant for the first time

Val Prefs by lazy {context.getsharedpreferences ("Kotlinlearndemo", Context.mode_private)}

· Internal are internal modified variables or classes that are visible inside the module.
. Inner represents the inner class
· init{} is equivalent to a free block in Java

init {
   println ("Initialize")
}

· inline defines an inline function
· <in xclass> is the equivalent of Java. Super xclass>
· <out xclass> is the equivalent of Java. Extend xclass>

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