java - 当我尝试添加到树集中时，它返回空白

Question

我有一份学校作业，这是我迄今为止所做的，其中记录了我正在尝试做的事情

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

public class UniquesDupesTester
{
    public static void main( String args[] ) throws IOException
    {
        // make a Scanner and associate it with "UniquesDupes.dat"
        // as long as there are Strings in the file

            // read in a String,
            // create a UniquesDupes object with it
            // print the object

            Scanner in = new Scanner(new File("UniquesDupes.dat"));



            while (in.hasNextLine())
            {
                String n = in.nextLine();
                UniquesDupes a = new UniquesDupes(n);
                a.getUniques();
                a.getDupes();
                System.out.println (a);
            }




    }
}

单独的文件

import java.util.Set;
import java.util.TreeSet;
import java.util.Arrays;
import java.util.ArrayList;

public class UniquesDupes
{
    private ArrayList<String> list;


    /**
     * constructs a UniquesDupes object such that list contains the space delimited strings
     * parsed from input
     * @param input a String containing the list of words separated by spaces
     */
    public UniquesDupes(String input)
    {
        list = new ArrayList<String>();

        String[] words = "abc cde fgh ijk".split(" ");
        ArrayList<String> list = new ArrayList<String>(Arrays.asList(words));
    }

    /**
     * returns a set of Strings containing each unique entry in the list
     */
    public Set<String> getUniques()
    {
        Set<String> uniques = new TreeSet<String>();

        for(String a:list)
        {
            uniques.add(a);
        }

        return uniques;
    }

    /**
     * returns a set of Strings containing each entry in the list that occurs more than once
     */
    public Set<String> getDupes()
    {
        Set<String> uniques = new TreeSet<String>();
        Set<String> dupes = new TreeSet<String>();

        for(String a:list)
        {
            uniques.add(a);
        {
            if(uniques.add(a) == false)
            {
                dupes.add(a);
            }
        }
        }


        return dupes;
    }

    /**
     * returns the original list, the list of duplicates and the list of uniques
     * @return the String version of the object
     */
    public String toString()
    {
        return "Orig list :: " + list
              + "\nDuplicates :: " + getDupes()
              + "\nUniques :: " + getUniques() + "\n\n";
    }
}

如果您需要的话，这是 dat 文件

a b c d e f g h a b c d e f g h i j k
one two three one two three six seven one two
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 6

它编译并运行，但所有文件都返回空白，我不知道我做错了什么，希望得到帮助或提示

Answer 1

逻辑几乎正确。

UniquesDupes 类几乎没问题，但构造函数却不太好。应该只是这样

public UniquesDupes() // no args, default constructor
{
    list = new ArrayList<String>(); //just initialize the list
}

同时，该类需要一个 addString 方法:

public void addString(String input) {
    String[] words = input.trim().split(" "); //split the input string into words by spaces, after trimming whitespace
    this.list.addAll(Arrays.asList(words)); //adding them to the list.
}

while 循环应该稍微改变一下。您只需要 UniquesDupes 类的 1 个实例，然后使用之前创建的 addString 方法添加每一行。

       UniquesDupes a = new UniquesDupes(); //create it here
       while (in.hasNextLine())
        {
            String n = in.nextLine();
            a.addString(n); //adding the string
        }

那么结果需要以不同的方式处理

            Collection<String> uniques = a.getUniques();
            Collection<String> dupes = a.getDupes();

            System.out.println (uniques.toString());
            System.out.println (dupes.toString());

也就是说，逻辑几乎是正确的......

您所做的一件丑陋的事情是这部分:

    list = new ArrayList<String>(); //using instance variable

    String[] words = "abc cde fgh ijk".split(" ");
    ArrayList<String> list = new ArrayList<String>(Arrays.asList(words));
    // ^^ declaring local variable the same name as the instance variable 

这不好。你不应该这样做。不，不。不要再这样做了!养成这种习惯会让代码变得异常难以阅读，并且维护起来非常疯狂......