数组未正确更新为“显示数组”类对象的数组在另一个类中初始化。

Question

我有一个名为cartList.txt的平面文件，还有两个名称为GetCachedCartList.java和AddToShoppingList.java的类。

我使用类GetCachedCartList.java从平面文件中获取数字(这是产品的in (我正在处理购物车的一个项目)，这些数字以表单num1#num2#num3#等形式写入文件中，这些数字被存储到该类的int数组变量中。

正如您所看到的，我使用了'#‘作为分隔符来区分不同的数字。

我使用类AddToShoppingList.java将文本"num#"添加到平面文件中的现有文本中。

当我尝试测试这两个类时，当GetCachedCartList.java在它自己的main方法中正确地输出cartList.txt中的数字时，问题就出现了，但是当我使用在AddToShoppingList.java的主方法中初始化的对象时，在添加了像"num#"这样的文本后，它给出了非常出乎意料的results.The数字num，似乎已经在帮助数组中添加了很多次，而不仅仅是一次，文本"num#"也被添加到平面文件的文本中，超过一次，但比数组中的文本少。

我怀疑这可能是由于不正确地使用循环，但无法发现任何错误。

cartList.txt

2#3#

GetCachedCartList.java

package Resources.utils.queries;

/**
 *
 * @author Aditya
 */

import java.io.File;
import java.util.Scanner;
import java.util.ArrayList;

public class GetCachedCartList {
    private static ArrayList<String> StringcartProdIdList = new ArrayList<String>();
    private static int[] cartProdIdList;

    public GetCachedCartList(){
        try{
            File cartListFile = new File("src/SessionData/productCachedData/cartList.txt");
            Scanner scann = new Scanner(cartListFile);
            scann.useDelimiter("#");
            while(scann.hasNext()){
                String s = scann.next();
                StringcartProdIdList.add(s); 
            }
            scann.close();

            cartProdIdList = new int[StringcartProdIdList.size()];
            for(int i = 0; i < StringcartProdIdList.size(); i++){
                cartProdIdList[i] = Integer.parseInt(StringcartProdIdList.get(i));
            }
        }
        catch (Exception ex) {
            System.out.println("Error:"+ex.getMessage());
        }
    }

    /**
     * @return the IDs of Items added in the Shopping Cart
     */
    public static int[] getCartProdIdList() {
        return cartProdIdList;
    }

    public static void main(String[] args){
        GetCachedCartList g = new GetCachedCartList();
        System.out.println("Length: "+g.getCartProdIdList().length);
        for(int i: g.getCartProdIdList()){
            System.out.println(i);
        }
    }
}

AddToShoppingList.java

package Resources.utils.queries;

/**
 *
 * @author Aditya
 */

import java.io.File;
import java.util.Scanner;
import java.io.PrintWriter;
import Resources.utils.queries.GetCachedCartList;

public class AddToShoppingList {
    public AddToShoppingList(int pid){
        try{
            GetCachedCartList gCCl = new GetCachedCartList();
            int[] initialCartListArr = gCCl.getCartProdIdList();
            String initialCartList = "";
            for(int i = 0; i < initialCartListArr.length; i++){
                initialCartList += initialCartListArr[i] + "#";
            }
            File cartListFile = new File("src/SessionData/productCachedData/cartList.txt");
            PrintWriter writer = new PrintWriter(cartListFile);
            writer.print("");
            writer.write(initialCartList);
            writer.write(pid+"#");
            writer.close();

        }
        catch(Exception e){
            System.out.println("Error:"+e.getMessage());
        }
    }

    public static void main(String[] args){
        GetCachedCartList gCCl1 = new GetCachedCartList();
        int[] initialCartListArr = gCCl1.getCartProdIdList();
        System.out.println("Initial cart list");
        for(int i = 0; i < initialCartListArr.length; i++){
            System.out.println(initialCartListArr.length+" : "+initialCartListArr[i]);
        }

        AddToShoppingList aTSL = new AddToShoppingList(9);

        System.out.println("Updated cart list");

        GetCachedCartList gCCl2 = new GetCachedCartList();
        int[] finalCartListArr = gCCl2.getCartProdIdList();
        for(int i = 0; i < finalCartListArr.length; i++){
            System.out.println(finalCartListArr.length+" : "+finalCartListArr[i]);
        }
    }
}

如果您首先运行GetCachedCartList.java，然后运行AddToShoppingList.java，则输出上述代码为：

GetCachedCartList.java

Length: 2
2
3

AddToShoppingList.java

Initial cart list
2 : 2
2 : 3
Updated cart list
9 : 2
9 : 3
9 : 2
9 : 3
9 : 2
9 : 3
9 : 2
9 : 3
9 : 9

现在平面文件有了文本

2#3#2#3#9#

哪里发生错误了？谢谢~

Answer 1

我希望我能正确地理解你对申请的想法。抱歉如果没有。因为String s = scann.next();返回"2, 3, \n“，所以有0，因为

AddToShoppingList.main {
    ...
    GetCachedCartList gCCl1 = new GetCachedCartList();
    ...
    GetCachedCartList gCCl2 = new GetCachedCartList();
}

我建议流动的代码：

输出

Error:null
Initial cart list
2 : 2
2 : 3
Error:null
Updated cart list
4 : 2
4 : 3
4 : 2
4 : 3

码

public class AddToShoppingList {
    public AddToShoppingList(int pid) {
        try {
            GetCachedCartList gCCl = new GetCachedCartList();
            List<Integer> initialCartListArr = gCCl.getCartProdIdList();
            String initialCartList = "";
            for (int i = 0; i < initialCartListArr.size(); i++) {
                initialCartList += initialCartListArr.get(i) + "#";
            }
            File cartListFile = new File("/home/ibondarenko/projects/demo/src/main/resources/cartList.txt");
            PrintWriter writer = new PrintWriter(cartListFile);
            writer.print("");
            writer.write(initialCartList);
            writer.write(pid + "#");
            writer.close();

        } catch (Exception e) {
            System.out.println("Error:" + e.getMessage());
        }
    }

    public static void main(String[] args) {
        GetCachedCartList gCCl1 = new GetCachedCartList();
        List<Integer> initialCartListArr = gCCl1.getCartProdIdList();
        System.out.println("Initial cart list");
        for (int i = 0; i < initialCartListArr.size(); i++) {
            System.out.println(initialCartListArr.size() + " : " + initialCartListArr.get(i));
        }

        AddToShoppingList aTSL = new AddToShoppingList(9);

        System.out.println("Updated cart list");

//        GetCachedCartList gCCl2 = new GetCachedCartList();
        List<Integer> finalCartListArr = gCCl1.getCartProdIdList();
        for (int i = 0; i < finalCartListArr.size(); i++) {
            System.out.println(finalCartListArr.size() + " : " + finalCartListArr.get(i));
        }
    }
}


public class GetCachedCartList {
    private static ArrayList<Integer> StringcartProdIdList = new ArrayList<Integer>();

    public GetCachedCartList() {
        try {
            File cartListFile = new File("/home/ibondarenko/projects/demo/src/main/resources/cartList.txt");
            Scanner scann = new Scanner(cartListFile);
            scann.useDelimiter("#");
            while (scann.hasNext()) {
                int s = scann.nextInt();
                StringcartProdIdList.add(s);
            }
            scann.close();
        } catch (Exception ex) {
            System.out.println("Error:" + ex.getMessage());
        }
    }

    /**
     * @return the IDs of Items added in the Shopping Cart
     */
    public static ArrayList<Integer> getCartProdIdList() {
        return StringcartProdIdList;
    }

    public static void main(String[] args) {
        GetCachedCartList g = new GetCachedCartList();
        System.out.println("Length: " + StringcartProdIdList.size());
        for (int i : g.getCartProdIdList()) {
            System.out.println(i);
        }
    }
}

Answer 2

我认为您可以首先简化代码：

一个具有从文件中读取ids并检索List<Integer>的逻辑的类

public final class ReadCartProdIds {

    private final File file;

    public ReadCartProdIds(File file) {
        this.file = file;
    }

    public List<Integer> apply() throws FileNotFoundException {
        try (Scanner scan = new Scanner(file)) {
            scan.useDelimiter("#");

            List<Integer> cartProdIds = new ArrayList<>();

            while (scan.hasNext()) {
                cartProdIds.add(scan.nextInt());
            }

            return cartProdIds.isEmpty() ? Collections.emptyList() : Collections.unmodifiableList(cartProdIds);
        }
    }
}

另一个要添加到此文件中的新pid (您甚至不必重新读取已存在的文件，只需向其添加新文本)：

public final class AddCarProdId {

    private final File file;

    public AddCarProdId(File file) {
        this.file = file;
    }

    public void apply(int pid) throws IOException {
        Files.write(file.toPath(), (pid + "#").getBytes(), StandardOpenOption.APPEND);
    }

}

最后，您的main程序可以如下所示：

public static void main(String[] args) throws IOException {
    File file = new File("d:/cartList.txt");
    printFile(file, "Initial cart list:");
    new AddCarProdId(file).apply(9);
    printFile(file, "Updated cart list");
}

private static void printFile(File file, String message) throws FileNotFoundException {
    System.out.println(message);

    List<Integer> cartProdIds = new ReadCartProdIds(file).apply();
    cartProdIds.forEach(cartProdId -> System.out.println(cartProdIds.size() + " : " + cartProdId));
}