similar to result3 but for more complex cases harder to do in one expression null check it with `if` expression and then use the value,
Val result3 = nullAble?.foo() ?: differentValue otherwise a default value using the elvis operator access it only if it is not null using safe operator, access it as non-null asserting that with a sure call Several options depending on the intent of the code you would use one of these, and all are idiomatic but have different results: val nullAble: Xyz? = createPossiblyNullXyz() Safe Call, or lastly giving something that is possibly null a default value using the ?: Elvis Operator. ( Checking for null in conditions), or asserting that it is surely not null using the !! sure operator, accessing it with a ?. println(kotliner as? Person).In Kotlin, a null-able value without being sure it is not null cannot be accessed. You can also define your own getter and setter methods class Person(age: Int, name: String) copy code Copy the code Safe conversion of types (as?) val kotliner: Kotliner =.
Var: the default value is getterand setter. Need to call the inherited constructor (default is no parameter constructor). extendsThe keyword is changed :, which is consistent with the interface implementation. notes are changed to overrideThe keywordīecause Kotlin's class is final by default, you need to add the open keyword to make it inheritable. Kotlin Val simpleClass = simpleClass (9) println(simpleclass.x) simpleclass.y () copies the code Copy the code Interface Definition Java SimpleClass simpleClass = new SimpleClass(9) (simpleClass.x) simpleClass.y() Copy the code Copy the code Intuitively, by omitting the new keyword, you no longer need new to get the object You can also define it directly on a class Class instantiation Use this if you need to define other constructors constructorKeyword creation The Kotlin class takes a no-parameter constructor by default. Kotlin class member variable, the method is similar to Java This section focuses on the type definition and simple use of Kotlin The definition of a class The Kotlin class defaults to public and has nothing to omit
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