扫描仪内部方法不要求输入

Question

我要求用户插入一个item name with extension ".txt"的项目名称，如果该item name与existing itemName.txt对应，则用户需要在他想要“传输”它的地方插入location name with extension ".txt" 。 如果一切正常，那么itemName.txt中的内容将被写入locationName.txt

我的主要是这样的：

package victor;

import java.io.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Scanner;

public class Main extends Item {
    public Main(String location, Integer length, Integer height, Integer depth) {
        super(location, length, height, depth);
    }

    public static void main(String[] args) throws IOException {
        List<Item> itemList = new ArrayList<>();
        List<Location> locationList = new ArrayList<>();
        System.out.println("Welcome to create new:");
        System.out.println("Please follow the steps:");
        HashMap<Integer, String> menu = new HashMap<>();
        menu.put(1, "Create Location");
        menu.put(2, "Create Item");
        menu.put(3, "Transfer to location");
        menu.forEach((key, value) -> System.out.println(key + "- " + value));
        int user_choice;
        Scanner userInputMenu = new Scanner(System.in);
        user_choice = userInputMenu.nextInt();
        switch (user_choice) {
            case 1:
                createLocationPlusFile(locationList);
            case 2:
                createItemPlusFile(itemList);
            case 3:
                transferItemToLocation(itemList, locationList);
        }
    }
}

当用户从 menu- 3输入时，程序正在关闭Process finished with exit code 0 。

这是我的项目 Class 和我写的方法：

package victor;

import java.io.*;
import java.util.List;
import java.util.Scanner;

public class Item extends Location {
    private String itemName;
    private Integer kg;
    private Integer length;
    private Integer height;
    private Integer depth;

    public Item(String itemName, Integer kg, Integer length, Integer height, Integer depth) {
        super();
        this.itemName = itemName;
        this.kg = kg;
        this.length = length;
        this.height = height;
        this.depth = depth;
    }


    public Item() {

    }

    public Item(String location, Integer length, Integer height, Integer depth) {
        super();
    }

    public String getItemName() {
        return itemName;
    }

    public void setItemName(String itemName) {
        this.itemName = itemName;
    }

    public Integer getKg() {
        return kg;
    }

    public void setKg(Integer kg) {
        this.kg = kg;
    }

    public Integer getLength() {
        return length;
    }

    public void setLength(Integer length) {
        this.length = length;
    }

    public Integer getHeight() {
        return height;
    }

    public void setHeight(Integer height) {
        this.height = height;
    }

    public Integer getDepth() {
        return depth;
    }

    public void setDepth(Integer depth) {
        this.depth = depth;
    }

    @Override
    public String toString() {
        return "Item{" +
                "itemName='" + itemName + '\'' +
                ", kg=" + kg +
                ", length=" + length +
                ", height=" + height +
                ", depth=" + depth +
                '}';
    }

    public static void createItemPlusFile(List<Item> itemList) throws NullPointerException, IOException {
        int defaultLength = 80;
        int defaultHeight = 205;
        int defaultDepth = 120;
        int defaultKg = 3500;
        Scanner in1 = new Scanner(System.in);
        System.out.println("Enter Item Name: ");
        String itemName = in1.nextLine();
        System.out.println("New Item created successfully!" + "\n" + itemName);


        int inLength;
        Scanner in2 = new Scanner(System.in);
        System.out.println("Enter Item height: ");
        int itemLength = in2.nextInt();
        if (itemLength > defaultLength) {
            System.out.println("Height that you added is to big, please use a height of max  205");
            inLength = in2.nextInt();
        } else {
            System.out.println("Height inserted correctly! ");
        }


        int inHeight;
        Scanner in3 = new Scanner(System.in);
        System.out.println("Enter Item height: ");
        int itemHeight = in3.nextInt();
        if (itemHeight > defaultHeight) {
            System.out.println("Height that you added is to big, please use a height of max  205");
            inHeight = in3.nextInt();
        } else {
            System.out.println("Height inserted correctly! ");
        }
        int inDepth;
        Scanner in4 = new Scanner(System.in);
        System.out.println("Enter Item depth: ");
        int itemDepth = in4.nextInt();
        if (itemDepth > defaultDepth) {
            System.out.println("Depth that you added is to big, please use a depth of max  120");
            inDepth = in4.nextInt();
        } else {
            System.out.println("Depth inserted correctly! ");
        }
        int inKg;
        Scanner in5 = new Scanner(System.in);
        System.out.println("Enter Item kg: ");
        int itemKg = in4.nextInt();
        if (itemKg > defaultKg) {
            System.out.println("kg that you added is to big, please use a depth of max  3500");
            inDepth = in4.nextInt();
        } else {
            System.out.println("Kg inserted correctly! ");
        }
        Item item = new Item(itemName, itemKg, itemLength, itemHeight, itemDepth);
        File file = new File(item.getItemName() + "CUSCAS001GRY-uk.txt");
        if (!file.exists()) {
            file.createNewFile();
        }
        FileWriter fileWriter = new FileWriter(item.getItemName() + "CUSCAS001GRY-uk.txt", true);
        fileWriter.write(item + "\n");
        fileWriter.close();
    }
//this method I wrote, I expect to ask user to input the item and if item with this name exist then he insert the location where he want to "transfer" it .
       public static void transferItemToLocation(List<Item> itemList, List<Location> locationList) throws IOException {
    for (Item item : itemList) {
        for (Location location : locationList) {
            Scanner inputItemTransfer = new Scanner(System.in);
            System.out.println("Insert the item you want to transfer + .txt  extension!");
            inputItemTransfer.nextLine();
            if (inputItemTransfer.nextLine()
                    .equalsIgnoreCase(item + ".txt")) {
                Scanner inputTransferToLocation = new Scanner(System.in);
                System.out.println("Insert the location where you want to transfer the item");
                inputTransferToLocation.nextLine();
                if (inputTransferToLocation.nextLine()
                        .equalsIgnoreCase(String.valueOf(location))) {
                    BufferedReader bufferedReader = new BufferedReader(new FileReader(String.valueOf(inputItemTransfer)));
                    FileWriter fileWriter = new FileWriter(inputTransferToLocation + ".txt", true);
                    BufferedWriter outputStream = new BufferedWriter(fileWriter);
                    String str;
                    while ((str = bufferedReader.readLine()) != null) {
                        outputStream.write(str + "\n");
                    }
                    outputStream.close();
                }
            }
        }
    }
  }
}

我假设我对扫描仪做错了什么。 非常感谢任何帮助/批评

Answer 1

您不需要为用户需要输入数据的每个提示创建扫描仪 object。 整个应用程序的一个扫描仪 object 就可以了。 只需在Main class 中将 object 声明为public static即可，例如：

public class Main extends Item {
    
    // Declare a Scanner object that can potentially be used anywhere.
    public static Scanner userInput = new Scanner(System.in).useDelimiter("\\R");


    public Main(String location, Integer length, Integer height, Integer depth) {
        super(location, length, height, depth);
    }

    public static void main(String[] args) throws IOException {
        // ... main() method code here ...
    }
}

然后在任何地方提示用户并需要使用 Scanner 方法获取输入，请使用Main.userInput。 相反，例如：

user_choice = Main.userInput.nextInt();

或者：

String itemName = Main.userInput.nextLine();

当使用Scanner#nextInt() （或任何 Scanner#nextXXX 方法）并且 Scanner# nextLine () 提示将直接跟随时，您很可能需要使用从 Scanner#nextInt( ） 利用。 nextInt()方法不像nextline()方法那样使用换行符，因此似乎跳过了使用nextLine()方法的提示。 在这种情况下，你会想要这样做：

user_choice = Main.userInput.nextInt();
Main.userInput.nextLine();

一个好的经验法则是：

如果您使用Scanner#nextLine()方法，则将其用于其他任何事情，根本不要使用它。 请改用next()和nextXXX()方法。

如果您按上面所示创建 Scanner（使用useDelimiter("\\R")方法），则Scanner#next()方法将返回类似于Scanner#nextLine()方法返回的内容。

---

目前，由于您使用 Scanner 方法的方式，您的transferItemToLocation()方法对方法中的每个提示进行双重提示。

public static void transferItemToLocation(List<Item> itemList, List<Location> locationList) throws IOException {
    for (Item item : itemList) {
        for (Location location : locationList) {
            Scanner inputItemTransfer = new Scanner(System.in);
            System.out.println("Insert the item you want to transfer + .txt  extension!");
            inputItemTransfer.nextLine();
            if (inputItemTransfer.nextLine()
                    .equalsIgnoreCase(item + ".txt")) {
                Scanner inputTransferToLocation = new Scanner(System.in);
                System.out.println("Insert the location where you want to transfer the item");
                inputTransferToLocation.nextLine();
                if (inputTransferToLocation.nextLine()
                        .equalsIgnoreCase(String.valueOf(location))) {
                    BufferedReader bufferedReader = new BufferedReader(new FileReader(String.valueOf(inputItemTransfer)));
                    FileWriter fileWriter = new FileWriter(inputTransferToLocation + ".txt", true);
                    BufferedWriter outputStream = new BufferedWriter(fileWriter);
                    String str;
                    while ((str = bufferedReader.readLine()) != null) {
                        outputStream.write(str + "\n");
                    }
                    outputStream.close();
                }
            }
        }
    }
}

我只能假设您为什么要这样做，因为您没有提供所有代码，这部分是为什么我在上面发布了很多关于 Scanner 的废话。 你在这里得到的东西不会像你想象的那样工作。 如前所述，摆脱所有这些 Scanner 对象并使用类似于Main class 中声明的内容（类似于本文开头显示的内容）。 声明名为inputItemTransfer和inputTransferToLocation的字符串变量。 将用户输入分别放入每个提示的这些变量中，并使用这些变量中包含的数据而不是扫描仪对象，例如：

public static void transferItemToLocation(List<Item> itemList, List<Location> locationList) throws IOException {
    String inputItemTransfer;
    String inputTransferToLocation;
    for (Item item : itemList) {
        for (Location location : locationList) {
            System.out.println("Insert the item you want to transfer + .txt  extension!");
            inputItemTransfer = Main.userInput.nextLine();
            if (inputItemTransfer.equalsIgnoreCase(item + ".txt")) {
                System.out.println("Insert the location where you want to transfer the item");
                inputTransferToLocation = Main.userInput.nextLine();
                if (inputTransferToLocation.equalsIgnoreCase(String.valueOf(location))) {
                    BufferedReader bufferedReader = new BufferedReader(new FileReader(String.valueOf(inputItemTransfer)));
                    FileWriter fileWriter = new FileWriter(inputTransferToLocation + ".txt", true);
                    BufferedWriter outputStream = new BufferedWriter(fileWriter);
                    String str;
                    while ((str = bufferedReader.readLine()) != null) {
                        outputStream.write(str + "\n");
                    }
                    outputStream.close();
                }
            }
        }
    }
}

这个方法现在是否正确地转到 function 真的超出了我的范围。 没有所有代码或至少没有最小的可重现示例，很难说。 我想一步一个脚印。

---

在一边：

正如评论中提到的那样，用户确实需要输入大量数据才能使用您的应用程序，这对某些人来说有点令人沮丧，而且实际上很难。 或许可以考虑使用更多基于菜单的系统，以减少进入要求并使使用体验更舒适。

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祝你好运。