如何使用Swift枚举等关联值创建Java枚举？

Edit: To be clear I am not asking how to do enums in java. I am asking if there is something in java that is complementary to Swifts associated values in enums. This is not just simply how do I store values on enums. Take a look at the example I provided and you will see the difference.

编辑:要明确我不会问如何在java中进行枚举。我在询问java中是否存在与枚举中的Swifts相关值互补的内容。这不仅仅是如何在枚举上存储值。看看我提供的示例,您将看到不同之处。

So an iOS developer was showing me an architecture where he used swifts enum associated values. This concept seemed interesting to me I and as an android developer I was curious to see if its possible in java without being overly verbose. What is the equivalent with Java enums? Or is it not possible?

因此,iOS开发人员向我展示了一个架构,他使用了swifts枚举关联值。这个概念对我来说似乎很有趣,作为一个Android开发人员,我很想知道它是否可以在Java中使用而不会过于冗长。与Java枚举相同的是什么?或者这不可能吗?

Here is an example of what I mean by Associated Values. Its pulled form the apple docs.

以下是关联值的一个例子。它从苹果文档中拉出来。

enum Barcode {
    case UPCA(Int, Int, Int, Int)
    case QRCode(String)
}

// Instantiated
var productBarcode = Barcode.UPCA(8, 85909, 51226, 3)
// or
productBarcode = .QRCode("ABCDEFGHIJKLMNOP")


switch productBarcode {
case .UPCA(let numberSystem, let manufacturer, let product, let check):
    println("UPC-A: \(numberSystem), \(manufacturer), \(product), \(check).")
case .QRCode(let productCode):
    println("QR code: \(productCode).")
}

2 个解决方案

#1

For me with Java enums this will not be possible.

对于使用Java枚举的我来说,这是不可能的。

To be close to your posted snippet you would be verbose, as you already assume.

如您已经假设的那样,要接近您发布的代码片段,您将会很详细。

enum

enum BarcodeType {
    UPCA,
    QRCode,
    UNDEFINED;
}

factory class

abstract class Barcode {

    abstract public BarcodeType getType();

    public static final Barcode newUPCA(int numberSystem, int manufacturer, int product, int check) {
        return new BarcodeUPCA(numberSystem, manufacturer, product, check);
    }

    public static final Barcode newQRCode(String productCode) {
        return new BarcodeQRCode(productCode);
    }
}

concrete implementation UPCA

具体实施UPCA

class BarcodeUPCA extends Barcode {
    private final int numberSystem;
    private final int manufacturer;
    private final int product;
    private final int check;

    public BarcodeUPCA(int numberSystem, int manufacturer, int product, int check) {
        this.numberSystem = numberSystem;
        this.manufacturer = manufacturer;
        this.product = product;
        this.check = check;
    }

    public int getNumberSystem() {
        return numberSystem;
    }

    public int getManufacturer() {
        return manufacturer;
    }

    public int getProduct() {
        return product;
    }

    public int getCheck() {
        return check;
    }

    @Override
    public BarcodeType getType() {
        return BarcodeType.UPCA;
    }
}

concrete implementation QRCode

具体实现QRCode

class BarcodeQRCode extends Barcode {

    private final String productCode;

    public BarcodeQRCode(String productCode) {
        this.productCode = productCode;
    }

    public String getProductCode() {
        return productCode;
    }

    @Override
    public BarcodeType getType() {
        return BarcodeType.QRCode;
    }
}

demo application

public class BarcodeMain {

    public static void main(String[] args) throws Exception {
        List<Barcode> barcodes = new ArrayList<>();
        barcodes.add(Barcode.newUPCA(8, 85909, 51226, 3));
        barcodes.add(Barcode.newQRCode("foobar"));

        for (Barcode barcode : barcodes) {
            switch (barcode.getType()) {
                case UPCA: {
                    BarcodeUPCA b = (BarcodeUPCA) barcode;
                    System.out.printf("UPC-A: %d, %d, %d, %d%n",
                            b.getNumberSystem(),
                            b.getManufacturer(),
                            b.getProduct(),
                            b.getCheck()
                    );
                    break;
                }
                case QRCode: {
                    BarcodeQRCode b = (BarcodeQRCode) barcode;
                    System.out.printf("QR code: %s%n", b.getProductCode());
                    break;
                }
                default:
                    System.err.println("unhandled type: " + barcode.getType());
            }
        }
}

output

UPC-A: 8, 85909, 51226, 3
QR code: foobar

#2

I also struggled with this question, and came up with the following solution. Notably, I don't even use enums, since Java's enums are not well-suited to the task. The important part is that you need switch-like behaviour for the cases, with the associated values available in each case.

我也在努力解决这个问题,并想出了以下解决方案。值得注意的是,我甚至不使用枚举,因为Java的枚举不适合这项任务。重要的是,您需要案例的类似开关的行为,并在每种情况下都提供相关的值。

enum-like type

public abstract class Barcode
{
    private Barcode() {}

    void caseUPCA(IntFunction<IntFunction<IntFunction<IntConsumer>>> action) {}
    void caseQRCode(Consumer<String> action) {}

    static Barcode UPCA(int numberSystem, int manufacturer, int product, int check)
    {
        return new Barcode()
        {
            @Override public void caseUPCA(IntFunction<IntFunction<IntFunction<IntConsumer>>> action)
            {
                action.apply(numberSystem).apply(manufacturer).apply(product).accept(check);
            }
        };
    }

    static Barcode QRCode(String text)
    {
        return new Barcode()
        {
            @Override public void caseQRCode(Consumer<String> action)
            {
                action.accept(text);
            }
        };
    }
}

demo application

public class BarcodeMain
{
    public static void main(String[] args) throws Exception
    {
        List<Barcode> barcodes = new ArrayList<>();
        barcodes.add(Barcode.UPCA(8, 85909, 51226, 3));
        barcodes.add(Barcode.QRCode("foobar"));

        for(Barcode barcode: barcodes)
        {
            barcode.caseUPCA(numberSystem -> manufacturer -> product -> check ->
                System.out.printf("UPC-A: %d, %d, %d, %d%n", numberSystem, manufacturer, product, check));
            barcode.caseQRCode(productCode ->
                System.out.printf("QR code: %s%n", productCode));
        }
    }
}

output

UPC-A: 8, 85909, 51226, 3
QR code: foobar

pros

• Much less implementation code than enum-based solutions

实现代码比基于枚举的解决方案少得多

• Even less code at usage site than enum-based solutions

使用网站上的代码甚至比基于枚举的解决方案更少

cons

• Lots of awkward nesting in Barcode implementation. Just Java being ugly.

Barcode实现中有很多笨拙的嵌套。只是Java丑陋。

• You can't throw exceptions from the switch case actions.

您不能从switch case操作中抛出异常。

• Angle bracket blindness in UPCA implementation, due to having many arguments. To prevent this leaking into the API, you could declare a public interface UPCAConsumer extends IntFunction<IntFunction<IntFunction<IntConsumer>>> {}, and use UPCAConsumer for the caseUPCA(action) argument type.

UPCA实施中的角括号盲,由于有许多参数。为了防止泄漏到API中,您可以声明一个公共接口UPCAConsumer扩展IntFunction >> {},并使用UPCAConsumer作为caseUPCA(action)参数类型。