The application and usage of the Google Collection framework in the Java class library

The Google Collect framework, also known as the Guava library, is a Java class library used to handle the collection.It provides many powerful functions and tools to simplify the operation of the collection and improve the readability and performance of the code.This article will introduce the application and usage of the Google Collect framework in the Java class library, and provide some Java code examples to help readers better understand. 1 Introduction The Google Collect framework is an open source project developed by Google. It extends the function of the collection of Java standard libraries and provides many useful tool classes and practical methods.It mainly has the following characteristics: -Function style: The Google Collect framework provides a rich functional programming style API, making the operation of the collection more concise and easy to read. -Suchimable collection: The Google Collection framework introduces the concept of unchanged collection. This collection cannot be changed and can improve thread security and performance. -The new collection type: Google Collect framework also introduces some new collection types, such as Multiset (allowing multiple repetitive elements), Multimap (collection of multiple values to multiple values), etc., providing more sets of setsOperation and use. 2. Common functions 2.1 Create a collection The Google Collect framework provides some convenient methods to create a collection object, such as: List<String> list = Lists.newArrayList("a", "b", "c"); Set<Integer> set = Sets.newHashSet(1, 2, 3); Map<String, Integer> map = Maps.newHashMap(); 2.2 Unchanged collection The unsatisfactory set in Google Collect framework refers to the collection that cannot be modified once it is created, which can improve the readability and thread security of the code.For example: ImmutableList<String> list = ImmutableList.of("a", "b", "c"); ImmutableSet<Integer> set = ImmutableSet.of(1, 2, 3); ImmutableMap<String, Integer> map = ImmutableMap.of("key1", 1, "key2", 2); 2.3 Collection operation The Google Collect framework provides many convenient methods to operate the collection objects, such as filtering, conversion, merger. filter: List<Integer> originalList = Lists.newArrayList(1, 2, 3, 4, 5); List<Integer> filteredList = originalList.stream() .filter(e -> e % 2 == 0) .collect(Collectors.toList()); Conversion: List<String> originalList = Lists.newArrayList("a", "b", "c"); List<String> transformedList = originalList.stream() .map(e -> e.toUpperCase()) .collect(Collectors.toList()); merge: List<Integer> list1 = Lists.newArrayList(1, 2, 3); List<Integer> list2 = Lists.newArrayList(4, 5, 6); List<Integer> mergedList = Streams.concat(list1.stream(), list2.stream()) .collect(Collectors.toList()); 2.4 New collection type The Google Collect framework also introduces some new collection types, such as Multiset, Multimap, etc.These collection types can meet certain special needs, such as the number of repetitions of statistical elements, mapping to multiple values. Multiset example: Multiset<String> multiset = HashMultiset.create(); multiset.add("a"); multiset.add("b"); multiset.add("a"); int count = multiset.count ("a"); // The return value is 2 Multimap example: Multimap<String, Integer> multimap = ArrayListMultimap.create(); multimap.put("key1", 1); multimap.put("key1", 2); multimap.put("key2", 3); Collection <neteger> Values = Multimap.get ("Key1"); // The return value is [1, 2] 3. Summary This article introduces the application and usage of the Google Collect framework in the Java class library.It provides many functions and tools to handle the collection, making the operation of the collection more concise and easy to read.By using the Google Collect framework, developers can process the collection data more efficiently and improve the quality and performance of the code.I hope this article can help readers better understand and use the Google Collect framework.