英文:
Why is this causing a runtime error? (finding word count of a string using HashMap)
问题
import java.util.HashMap;
import java.util.Iterator;
class L6ex1pt2 {
String line = "当我在那里时，它也在那里"; //适用于所有唯一单词的字符串，但不适用于有重复单词的字符串（如此）
public static void main(String[] args) {
L6ex1pt2 test = new L6ex1pt2();
HashMap<String, Integer> hash = new HashMap<String, Integer>();
hash = test.countWords(test.line);
}
public String[] words(String s) {
String[] words = s.split("\\s+");
return words;
}
public HashMap<String, Integer> countWords(String s) {
HashMap<String, Integer> wordCount = new HashMap<String, Integer>();
String[] werds = words(s);
for (String w : werds) {
if (wordCount.containsKey(w)) {
wordCount.put(w, wordCount.get(w) + 1);
} else {
wordCount.put(w, 1);
}
}
return wordCount;
}
}
此代码部分已被翻译。
英文:
import java.util.HashMap;
import java.util.Iterator;
class L6ex1pt2 {
String line = "When I was there, it was there"; //works for Strings with all unique words
//but not for Strings with repeated words (like this)
public static void main(String[] args) {
L6ex1pt2 test = new L6ex1pt2();
HashMap<String, Integer> hash = new HashMap<String, Integer>();
hash = test.countWords(test.line);
}
public String[] words(String s) {
String[] words = s.split("\\s+");
return words;
}
public HashMap<String, Integer> countWords(String s) {
HashMap<String, Integer> wordCount = new HashMap<String, Integer>();
String[] werds = words(s);
for (String w: werds) {
if (wordCount.containsKey(w)) {
wordCount.put(w, wordCount.get(s)+1);
} else {
wordCount.put(w, 1);
}
}
return wordCount;
}
}
Throws this exception:
Exception in thread "main" java.lang.NullPointerException
at L6ex1pt2.countWords(L6ex1pt2.java:24)
at L6ex1pt2.main(L6ex1pt2.java:10)
答案1
得分: 1
Line 25
wordCount.put(w, wordCount.get(s)+1);
应更改为
wordCount.put(w, wordCount.get(w)+1);
因为变量 s 包含整个字符串，而不是您期望用作哈希映射键的单词。
英文:
Line 25
wordCount.put(w, wordCount.get(s)+1);
should be
wordCount.put(w, wordCount.get(w)+1);
Since s contains the whole string and not the word you expect for the hashmap key.
答案2
得分: 0
在你的第24行代码中，你错误地写成了：
wordCount.put(w, wordCount.get(s)+1);
应该是：
wordCount.put(w, wordCount.get(w)+1);
英文:
In your line number 24, you have wrongly written:
wordCount.put(w, wordCount.get(s)+1);
It should be:
wordCount.put(w, wordCount.get(w)+1);
答案3
得分: 0
将 get(s)+1 替换为 get(w)+1。
完整代码：
import java.util.HashMap;
import java.util.Iterator;
public class Main {
String line = "When I was there it was there";
public static void main(String[] args) {
Main test = new Main();
HashMap<String, Integer> hash = new HashMap<String, Integer>();
hash = test.countWords(test.line);
System.out.println(hash);
}
public HashMap<String, Integer> countWords(String s) {
HashMap<String, Integer> wordCount = new HashMap<String, Integer>();
String[] wordsArr = words(s);
for (String w: wordsArr) {
if (wordCount.containsKey(w)) {
wordCount.put(w, wordCount.get(w)+1);
} else {
wordCount.put(w, 1);
}
}
return wordCount;
}
public String[] words(String s) {
String[] words = s.split("\\s+");
return words;
}
}
输出：
{When=1, there=2, was=2, I=1, it=1}
英文:
Replace get(s)+1 with get(w)+1
Full code :
import java.util.HashMap;
import java.util.Iterator;
public class Main {
String line = "When I was there it was there";
public static void main(String[] args) {
Main test = new Main();
HashMap<String, Integer> hash = new HashMap<String, Integer>();
hash = test.countWords(test.line);
System.out.println(hash);
}
public HashMap<String, Integer> countWords(String s) {
HashMap<String, Integer> wordCount = new HashMap<String, Integer>();
String[] wordsArr = words(s);
for (String w: wordsArr) {
if (wordCount.containsKey(w)) {
wordCount.put(w, wordCount.get(w)+1);
} else {
wordCount.put(w, 1);
}
}
return wordCount;
}
public String[] words(String s) {
String[] words = s.split("\\s+");
return words;
}
}
Output :
{When=1, there=2, was=2, I=1, it=1}
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