java - 如何让数组列表在另一个类java中调用

Question

我需要编写一段代码来检查数组列表中的所有单词，并告诉我其中有多少单词具有一定的长度。我知道如何做到这一点，但我不知道如何使 ArrayList 在第二个类中被读取，以便我可以在程序中应用它。

主要

import java.util.Scanner;
class Main {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    java.util.ArrayList myList = new java.util.ArrayList();
    myList.add("cat");
    myList.add("mouse");
    myList.add("frog");
    myList.add("dog");
    myList.add("dog");
    int len = in.nextInt();
    WordList wl = new WordList();
    wl.numWordsOfLength(len);
  }
}

二等

public class WordList{
  public int numWordsOfLength(int len){
    int count = 0;
    for(int i=0;i<len;i++){

      if(((String)myList.get(i)).length()==len){
        count++;
      }
    }
    return count;
  }
}

Answer 1

您需要将列表作为参数传递:

  public int numWordsOfLength(int len, List<String> myList){
    int count = 0;
    for(int i=0;i<myList.size;i++){

      if((myList.get(i)).length()==len){
        count++;
      }
    }
    return count;
  }

或通过WordList构造函数:

import java.util.List;
public class WordList{

    private final List<String> myList;
    WordList(List<String> myList){
        this.myList = myList;
    }
    public int numWordsOfLength(int len){
        int count = 0;
        for (String s : myList) {
            if (s.length() == len) {
                count++;
            }
        }
        return count;
    }
}

侧节点而不是:

    java.util.ArrayList myList = new java.util.ArrayList();

就这样做:

   import java.util.List;
   ....
   List<String> myList = new ArrayList();

完整运行示例:

public class Test {

    public static class WordList{

        private final List<String> myList;
        WordList(List<String> myList){
            this.myList = myList;
        }
        public int numWordsOfLength(int len){
            int count = 0;
            for (String s : myList) {
                if (s.length() == len) {
                    count++;
                }
            }
            return count;
        }
    }


        public static void main(String[] args) {
            Scanner in = new Scanner(System.in);
            List<String> myList = new ArrayList<>();
            myList.add("cat");
            myList.add("mouse");
            myList.add("frog");
            myList.add("dog");
            myList.add("dog");
            int len = in.nextInt();
            WordList wl = new WordList(myList);
            System.out.println(wl.numWordsOfLength(len));
        }
}