9/16/2023 0 Comments Java array init![]() ![]() How then is Scala’s Array represented? In fact a generic array like Array could be at run-time any of Java’s eight primitive array types byte, short, char, int, long, float, double, boolean, or it could be an array of objects. What about genericity? In Java, you cannot write a T where T is a type parameter. So now you know how arrays can be compatible with sequences and how they can support all sequence operations. So if both conversions are applicable, the one in Predef is chosen. Implicits in subclasses and subobjects take precedence over implicits in base classes. The first is defined in the Predef object whereas the second is defined in a class scala.LowPriorityImplicits, which is inherited by Predef. The ArrayOps conversion has a higher priority than the WrappedArray conversion. ![]() The answer to that question is that the two implicit conversions are prioritized. After all, both conversions map an array to a type that supports a reverse method, which is what the input specified. This raises the question of how the compiler picked intArrayOps over the other implicit conversion to WrappedArray in the line above. Where intArrayOps is the implicit conversion that was inserted previously. The difference between the two implicit conversions on arrays is shown in the next REPL dialogue: Modern VMs often avoid creating this object entirely. Typically, this ArrayOps object is short-lived it will usually be inaccessible after the call to the sequence method and its storage can be recycled. “Adding” means that the array is wrapped in another object of type ArrayOps which supports all sequence methods. This conversion simply “adds” all sequence methods to arrays but does not turn the array itself into a sequence. There is yet another implicit conversion that gets applied to arrays. The last REPL line above shows that wrapping and then unwrapping with toArray gives the same array you started with. To go the other way, from a WrappedArray to an Array, you can use the toArray method defined in Traversable. The interaction above demonstrates that arrays are compatible with sequences, because there’s an implicit conversion from arrays to WrappedArrays. Instead, there is an implicit “wrapping” conversion between arrays and instances of class, which is a subclass of Seq. It can’t really be that because the data type representation of a native array is not a subtype of Seq. In Scala 2.8 an array does not pretend to be a sequence. Instead, the Scala 2.8 array implementation makes systematic use of implicit conversions. There were some puzzling corner cases and the performance of array operations was not all that predictable. The details of this were quite complicated, in particular when one created a new array of generic type Array. Previously, the Scala compiler somewhat “magically” wrapped and unwrapped arrays to and from Seq objects when required in a process called boxing and unboxing. You could potentially improve performance by not catching the exception ( see this question for more on this) and use a different method to check for valid integers.Given that Scala arrays are represented just like Java arrays, how can these additional features be supported in Scala? In fact, the answer to this question differs between Scala 2.8 and earlier versions. In this case bad input (not a valid integer) the element will be null. If you need to know about invalid input later you could do the following: Integer numbers = new Integer The reason we should trim the resulting array is that the invalid elements at the end of the int will be represented by a 0, these need to be removed in order to differentiate between a valid input value of 0. at the end which will need to be trimmed Now there will be a number of 'invalid' elements Do nothing or you could print error if you want If you don't need to know about invalid input but just want to continue parsing the array you could do the following: int index = 0 You will need to consider what you want need to do in this case, do you want to know that there was bad input at that element or just skip it. Numbers = Integer.parseInt(numberStrs) Īs YoYo's answer suggests, the above can be achieved more concisely in Java 8: int numbers = Arrays.stream(line.split(",")).mapToInt(Integer::parseInt).toArray() and another index for the numbers if to continue adding the others (see below) If you want to check then add a try/catch Note that this is assuming valid input You could read the entire input line from scanner, then split the line by, then you have a String, parse each number into int with index one to one matching.(assuming valid input and no NumberFormatExceptions) like String line = scanner.nextLine() ![]()
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