61B-11: Libraries, Abstract Classes, Packages

HHZZ included in UCB-CS61B

2024-07-14 217 words 2 minutes

Contents

Java Libraries

Collections

Collections is a package in Java that provides various utility classes for working with collections.

Tasks引入

3 tasks, given the text of a book:

Create a list of all words in the book.
Count the number of unique words.
Keep track of the number of times that specific words are mentioned.

#1 way set

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public static int countUniqueWords(List<String> words) {
	Set<String> ss = new HashSet<>();
	for (String s : words) {
   	    ss.add(s);    	
	}
	return ss.size();
}
public static int countUniqueWords(List<String> words) {
	Set<String> ss = new HashSet<>();
	ss.addAll(words);
	return ss;
}

#2 way map

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public static Map<String, Integer> 
        collectWordCount(List<String> words, List<String> targets) {
	Map<String, Integer> wordCounts = new HashMap<>();
	for (String s : targets) {
   	    wordCounts.put(s, 0);
	}
	for (String s : words) {
   	    if (wordCounts.containsKey(s)) {
          	int oldCount = wordCounts.get(s);
         	wordCounts.put(s, oldCount + 1);
   	    }      	
	}
	return wordCounts;
}