如何在特定情況下將此數組轉換為列表？

Question

我已經遍歷了數組B 檢查arrayList A是否存在公共元素。 然后刪除這些元素，並打印出A作為數組。

但是我的問題是如何打印出A （在我的程序中是System.out.println(crIss.get(m)); ）作為arrayList（只是一個沒有[]括號的元素列表）而不是數組？

這是我正在處理的完整代碼：

package issuetracking;

import java.util.*;

public class IssueTrackingObject {

    ArrayList<String> crIss = new ArrayList<String>();

    Scanner input = new Scanner(System.in);
    boolean crIss_bool;
    int numOfSolvedIss;
    private String[] solvedIss;

    //lets user create some issues and add them into an arrayList
    public void createIssue() {
        System.out.println("Enter 5 issues: ");

        for (int i = 0; i < 5; i++) {
            System.out.println("Issue " + (i + 1 + ": "));
            crIss_bool = crIss.add(input.nextLine());
        }

    }
//Let user mark some issues as solved (which are already in the list that the user has just created)

    public void solvedIssue() {
        System.out.println("How many solved issue you have(Must be less than 5): ");
        numOfSolvedIss = input.nextInt();

        solvedIss = new String[numOfSolvedIss];

        for (int k = 0; k < numOfSolvedIss; k++) {
            System.out.print("Enter solved issue(REMEMBER THAT THE SOLVED ISSUE MUST BE FROM ONE OF THEM YOU ALREADY HAVE CREATED)no. " + (k + 1) + ": ");

            solvedIss[k] = input.next();
        }

    }

    public void printUnsolvedIssue() {

for(int m=0; m<solvedIss.length;m++){
      crIss_bool = crIss.remove(solvedIss);

    System.out.println(crIss.get(m));   
}


    }


    public void printSolvedIssue() {
        System.out.println("");
        System.out.println("LIST OF SOLVED ISSUE:");

        for (int l = 0; l < solvedIss.length; l++) {
            System.out.printf("%s ", solvedIss[l]);
        }

    }

}

主類：

package issuetracking;

import java.util.*;

public class IssueTracking {

    static Scanner input = new Scanner(System.in);

    public static void main(String[] args) {
        IssueTrackingObject its = new IssueTrackingObject();

        System.out.println("                            WELCOME TO ISSUE TRACKING SYSTEM!\n\n");
        System.out.println("Choose from menu: ");
        System.out.println("1. Create new issue\n2. Mark issue(s) as solved\n"
                + "3. View solved issue(s)\n4. View unsolved issue(s)");
        System.out.println("Enter you choise:");
        //String userChoise = input.next();
        //switch-case

        while (true) {
            String userChoise = input.next();

            switch (userChoise) {
                case "1":
                    //System.out.println("Enter 5 issues: ");
                    //call appropriate issue
                    its.createIssue();
                    break;
                case "2":
                    //System.out.println("Mark solved issues (You must enter at least one issue): ");
                    //call appropriate issue
                    its.solvedIssue();
                    break;
                case "3":
                    System.out.println("Solved issue: ");
                    //call appropriate method
                    its.printSolvedIssue();
                    break;

                case "4":
                    System.out.println("Usolved issue: ");
                    //call appropriate issue
                    its.printUnsolvedIssue();
                    break;
                default:
                    System.out.println("Invalid input");
                    break;

            }

        }

    }

}

Answer 1

當您打印類似ArrayList的對象時，您遇到的打印行為是因為Java調用了Class的.toString()方法。 ArrayList.toString()繼承自AbstractCollection.toString() ，該文檔可在此處找到。

我建議更改此行為的方法是創建一個類似於以下內容的單獨的Print函數：

public void printList(ArrayList<String> list)
{
     for(String str : list)
     {
          System.out.print(str+" ");
     }
     System.out.println();
}

然后調用此函數代替您的打印語句：

printList(crIss);

請注意，此打印將在一行上打印列表中的每個元素，並用空格隔開。

Answer 2

有幾種方法可以做到這一點。 我給你看三個：

1. 將數據存儲在String並刪除不需要的字符：

    String tmp = crIss.toString(); tmp = tmp.substring(1, tmp.length() - 1); System.out.println(tmp); 

2. 與上述方法類似，但使用replace ：

    String tmp = crIss.toString().replace('[', '\\0').replace(']', '\\0'); System.out.println(tmp); 

3. 遍歷List並將值存儲在StringBuilder ：

    StringBuilder sb = new StringBuilder(); for (String string : crIss) { sb.append(string).append(", "); } sb.remove(sb.length() - 2, sb.length()); System.out.println(sb.toString()); 

Answer 3

只需遍歷crIss並打印其中的每個項目，然后打印所需的定界符即可。 在此示例中，我將用“，”分隔項目。

public void printUnsolvedIssue() {

   for(int m=0; m<solvedIss.length;m++){
       crIss.remove(solvedIss[i]);
   }

   for(int i = 0; i < crIss.size(); i++) {
       System.out.print(crIss.get(i));
       // only print the delimiter if it isn't the last item in the list
       if(i < crIss.size() - 1) {
           System.out.print(", ");
       }
   }
}

還要注意，我將crIss.remove(solvedIss)部分更改為crIss.remove(solvedIss[i]) 。 這樣，它將刪除solvedIss中的每個項目。