Please tell me, is there any difference (in terms of Java) in this examples:
object DefaultValues {
val FILES_TO_DOWNLOAD = 100
}
和
class DefaultValues {
companion object {
val FILES_TO_DOWNLOAD = 100
}
}
没有类或对象包装器:
const val DEFAULT_FILES_TO_DOWNLOAD = 100
和
val DEFAULT_FILES_TO_DOWNLOAD = 100
What is the true way to define?:
public static final int FILES_TO_DOWNLOAD = 100
You can use Kotlin bytecode viewer to find out what these options are compiled to.
With Kotlin 1.0.2 the compiled bytecode shows that
object或companion object中的val属性被编译为类内的private static final字段:
// access flags 0x1A
private final static I FILES_TO_DOWNLOAD = 100
还有一个getter，在引用属性时称为:
// access flags 0x1019
public final static synthetic access$getFILES_TO_DOWNLOAD$cp()I
在Java中，getter可以分别称为DefaultValues.INSTANCE.getFILES_TO_DOWNLOAD()或DefaultValues.Companion.getFILES_TO_DOWNLOAD().
Non-const top level property is compiled to the same to (1) with only difference that the field and getter are placed inside FilenameKt class now.
但是顶级const val被编译成public static final字段:
// access flags 0x19
public final static I DEFAULT_FILES_TO_DOWNLOAD = 100
The same public static final field will be produced when a const val is declared inside an object. Also, you can achieve the same resulting bytecode if you add @JvmField annotation to the properties declared in (1).
Concluding that, you can define public static final field using const or @JvmField either in an object or at top level.