如何比较 Java 中的对象？

Question

I have a data class written in Kotlin which has server error objects.

How can I check which object it is?

I can do it in Kotlin like this

when (failure) {
    is Failure.ServerError -> test()//do something
    is Failure.ServerErrorConflict -> test()//do something
}

The same thing I want to do it in Java:

switch (failure) {
    case failure == Failure.ServerErrorConflict:
        break;
}

But I get an error expression expected

This is my data class

sealed class Failure {
    object NetworkConnection : Failure()
    object ServerError : Failure()
    object ServerErrorConflict : Failure()

    /** * Extend this class for feature specific failures.*/
    abstract class FeatureFailure : Failure()
}

Please suggest how to do this.

Answer 1

Generally in java, object references are compared to type using instanceof binary operator.

In future versions of Java, for some types, if-else conditions with instanceof equality check is not needed and a switch can be used. The sealed classes feature providing this benefit is being previewed currently in Java 15 , and being previewed again in the upcoming Java 16 .

    switch (failure) {
        case NetworkConnection nc -> <do the required operation>
        case ServerError se -> <do the required operation>
        case ServerErrorConflict sec -> <do the required operation>
    }

Note - switch expressions

• break is not needed(will not fall through)
• value can be returned

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