Hashmap get函数返回null [英] Hashmap get function returns null

问题描述

我有一个hashmap，它是

  public HashMap< String，ArrayList< Integer>> invertedList; 
  

  invertedList.toString（）：{ryerson = [0,2,3]，23 = [3]，award = [1]，andisheh = [0,2 ]}
  

在我输入的同一个观察列表中：

  invertedList.get（ryerson）
  

我得到null作为结果，也在代码中。正如你所看到的，ryerson已经在我的invertedList中作为关键字了，我应该得到[0,2,3] !!!这里发生了什么？我很困惑！

我知道ArrayList存在一个值问题，因为我测试了Integer作为值，它工作正常，但仍然不知道如何解决它。我是java的新手，曾经与C＃一起工作。

invertedList的完整代码：

  public class InvertedIndex {
 public HashMap< String，ArrayList< Integer>> invertedList; 
 public ArrayList< String>文件; 
 public InvertedIndex（）{
 invertedList = new HashMap< String，ArrayList< Integer>>（）; 
 documents = new ArrayList< String>（）; 
} 
 public void buildFromTextFile（String fileName）throws IOException {
 FileReader fileReader = new FileReader（fileName）; 
 BufferedReader bufferedReader = new BufferedReader（fileReader）; 
 int documentId = 0; 
 while（true）{
 String line = bufferedReader.readLine（）; 
 if（line == null）{
 break; 
} 
 String [] words = line.split（\\W +）; 
 for（String word：words）{
 word = word.toLowerCase（）; 
 if（！invertedList.containsKey（word））
 invertedList.put（word，new ArrayList< Integer>（））; 
 invertedList.get（word）.add（documentId）; 
 
} 
 documents.add（line）; 
 documentId ++; 
} 
 bufferedReader.close（）; 
} 
  

测试代码：

  @Test 
 public void testBuildFromTextFile（）throws IOException {
 InvertedIndex invertedIndex = new InvertedIndex（）; 
 invertedIndex.buildFromTextFile（input.tsv）; 
 Assert.assertEquals（{ryerson = [0,2,3]，23 = [3]，award = [1]，andisheh = [0,2]}，invertedIndex.invertedList.toString（）） ; 
 ArrayList<整数> resultIds = invertedList.get（ryerson）; 
 ArrayList<整数> expectedResult = new ArrayList< Integer>（）; 
 expectedResult.add（0）; 
 expectedResult.add（2）; 
 expectedResult.add（3）; 
 Assert.assertEquals（expectedResult，resultIds）; 
} 
  

第一个Assert工作正常，第二个，resultIds为null。如果我正在阅读这个权利，并假设正确，这个测试函数是在InvertedIndex类中。我只是做了这个假设，因为这一行

  ArrayList< Integer> resultIds = invertedList.get（ryerson）; 
  

实际上应该是不可编译的，因为没有称为invertedList的局部变量。

该行应为

  ArrayList< Integer> resultIds = invertedIndex.invertedList.get（ryerson）; 
  

I have a hashmap which is

public HashMap<String, ArrayList<Integer>> invertedList;

I show you my invertedList in watch list during debugging:

invertedList.toString(): "{ryerson=[0, 2, 3], 23=[3], award=[1], andisheh=[0, 2]}"

In the same watch list when I enter:

invertedList.get("ryerson")

I get null as result, also in the code. As you can see "ryerson" is already there as a key in my invertedList and I should get [0, 2, 3] as a result!!! What is happening here? I'm so confused!

I know there is a problem with ArrayList as values, because I tested Integer as values and it worked fine, but still don't know how to solve it. I am new to java, used to work with C#.

The complete code of invertedList:

public class InvertedIndex {
public HashMap<String, ArrayList<Integer>> invertedList;
public ArrayList<String> documents; 
public InvertedIndex(){
    invertedList = new HashMap<String, ArrayList<Integer>>();
    documents = new ArrayList<String>();
}
public void buildFromTextFile(String fileName) throws IOException {
    FileReader fileReader = new FileReader(fileName);
    BufferedReader bufferedReader = new BufferedReader(fileReader);
    int documentId = 0;
    while(true){
        String line = bufferedReader.readLine();
        if(line == null){
            break;
        }
        String[] words = line.split("\\W+");
        for (String word : words) {
            word = word.toLowerCase();
            if(!invertedList.containsKey(word))
                invertedList.put(word, new ArrayList<Integer>());
            invertedList.get(word).add(documentId);

        }
        documents.add(line);
        documentId++;
    }
    bufferedReader.close();
}

The test code:

@Test
public void testBuildFromTextFile() throws IOException {
    InvertedIndex invertedIndex = new InvertedIndex();
    invertedIndex.buildFromTextFile("input.tsv");
    Assert.assertEquals("{ryerson=[0, 2, 3], 23=[3], award=[1], andisheh=[0, 2]}", invertedIndex.invertedList.toString());      
    ArrayList<Integer> resultIds =  invertedList.get("ryerson");
    ArrayList<Integer> expectedResult = new ArrayList<Integer>();
    expectedResult.add(0);
    expectedResult.add(2);
            expectedResult.add(3);
    Assert.assertEquals(expectedResult, resultIds);
}

The first Assert works fine, the second one, resultIds is null.

解决方案

If I'm reading this right, and assuming correctly, this test function is inside the InvertedIndex class. I only make that assumption because the line

ArrayList<Integer> resultIds =  invertedList.get("ryerson");

should actually be uncompilable as there is no local variable called "invertedList".

That line should read

ArrayList<Integer> resultIds =  invertedIndex.invertedList.get("ryerson");

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