如何使用 Lambda 解析字符串列表并将值添加到映射 <String,Integer>

Question

在我的控制台项目中，我在一行中收到输入 {String resource} {int quantity}（可以收到多对示例：3 Motes 5 stones 5 Shards

我的目标是重构 while 循环的主体以使用尽可能多的 lambda。我很想减少大量的 if-else 语句并使用谓词，但我是一个新手，我更想寻找其他我可以尝试的指针。

我已经查看了收集器的 javadoc，Arrays.stream() 并通读了 Oracle JDK 8 lambdas 和函数式编程中的教程，但显然需要更多实际示例。

目标是获得 250 个资源用于其中一个传奇地图键并停止程序。我用 Scanner 解析这些值，用一个空格分隔并按如下方式实现我的逻辑：

private final static int REQUIRED_QUANTITY = 250;
private static boolean gameOver = false;
Map<String, String> legendary = new HashMap<>();
        legendary.put("shards", "Shadowmourne");
        legendary.put("fragments", "Valanyr");
        legendary.put("motes", "Dragonwrath");

        Map<String, Integer> resources = new HashMap<>();

        while (true) {
            String[] loot = scanner.nextLine().toLowerCase().split(" ");
            String material = null;
            int quantity = 0;

            for (int i = 0; i < loot.length; i++) {
                if (i % 2 != 0) {
                    material = loot[i];
                } else {
                    quantity = Integer.parseInt(loot[i]);
                }

                if (material != null && quantity != 0) {
                    if (resources.containsKey(material.toLowerCase())) {
                        resources.replace(material, resources.get(material) + quantity);
                    }
                    resources.putIfAbsent(material.toLowerCase(), quantity);

                    material = null;
                    quantity = 0;
                }
            }

            resources.forEach((s, integer) -> {
                if (integer > REQUIRED_QUANTITY) {
                    System.out.println("Legendary obtained: " + legendary.get(s));
                    gameOver = true;
                }
            });

Answer 1

我做了一些修改。

仅对 2 个值使用 for 循环。一次只处理一行。
使用compute处理更新地图
放入占位符以检查正确的资源（输入时可能拼写错误。

private final static int REQUIRED_QUANTITY = 250;
private static boolean gameOver = false;

Map<String, String> legendary = new HashMap<>();
legendary.put("shards", "Shadowmourne");
legendary.put("fragments", "Valanyr");
legendary.put("motes", "Dragonwrath");
    
Map<String, Integer> resources = new HashMap<>();
Scanner scanner = new Scanner(System.in);
while (!gameOver) {
    String[] loot =
            scanner.nextLine().toLowerCase().split("\s+");
    for (int i = 0; i < loot.length; i+=2) {
    String material = loot[i+1];
    if (!legendary.containsKey(material)) {
        // do some error processing
    }
        int quantity = Integer.parseInt(loot[i]);   
        // you may want to catch exception here.
        resources.compute(material.toLowerCase(),
                (k, v) -> v == null ? quantity : v + quantity);
    
    }
    resources.forEach((s, integer) -> {
        if (integer > REQUIRED_QUANTITY) {
            System.out.println("Legendary obtained: "
                    + legendary.get(s));
            gameOver = true;
        }
    });
}

Answer 2

我已将您提供的代码封装到 class。

映射resources重命名并更改为实例变量Map<String, Integer> resourceToQuantity。标志 gameOver 也被制成实例变量。

主要 game-logic 位于 collectResources() 方法中，主要增强功能在此处进行：

标志 gameOver 用作 while loop 的退出条件；
nested for loop 的条件已更改；
缩短了 for loop，删除了 if/else 语句；
变量 quantity 和 material 的范围已缩小；
在循环的每次迭代中合并 quantity 并根据 REQUIRED_QUANTITY;
如果这种情况是肉标志 gameOver 被设置为 true 并且 game-loop 退出。
正在打印收集到的资源。

public class LootHunter {
    private final static int REQUIRED_QUANTITY = 250;
    private static final Map<String, String> legendary = Map.of(
            "shards", "Shadowmourne",
            "fragments", "Valanyr",
            "motes", "Dragonwrath"
    );

    private final Map<String, Integer> resourceToQuantity;
    private boolean gameOver;

    public LootHunter() {
        this.resourceToQuantity = new HashMap<>();
    }

    public void collectResources() {
        while (!gameOver) {
            Scanner scanner = new Scanner(System.in);
            String[] loot = scanner.nextLine().toLowerCase().split(" ");

            for (int i = 0; i < loot.length - 1; i += 2) {
                int quantity = Integer.parseInt(loot[i]);
                String material = loot[i + 1];
                int totalQuantity = resourceToQuantity.merge(material, quantity, Integer::sum); // merges quantities and returns the sum

                if (totalQuantity > REQUIRED_QUANTITY) {
                    System.out.printf("You win! %d of %s have been collected.%n", totalQuantity, material);
                    System.out.println("Legendary item obtained: " + legendary.get(material));
                    gameOver = true;
                    break;
                }
            }
        }
        printAllResources(); // prints all the collected resources
    }

    public void printAllResources() {
        System.out.println("List of resources collected:");
        resourceToQuantity.forEach((material, quantity) ->
                System.out.printf("%s: %d%n", material, quantity));
    }

    public static void main(String[] args) {
        LootHunter lootHunter = new LootHunter();
        lootHunter.collectResources();
    }
}

输入：

"30 shards 10 fragments 50 motes 80 fragments 70 shards 180 fragments"

输出

You win! 270 of fragments have been collected.
Legendary item obtained: Valanyr
List of resources collected:
shards: 100
motes: 50
fragments: 270

如何使用 Lambda 解析字符串列表并将值添加到映射 <String,Integer>

How To Parse A List Of Strings And Add Values to a Map<String,Integer> Using Lambdas

java

lambda

functional-programming