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  • [Java] Collections Intro example

    public class Code {
      public static void main(String[] args) {
        List<String> names = Arrays.asList("Paul", "Jane", "Sam", "Michaela");
    
        // Way to sort prior to Java 8 lambdas
        Collections.sort(names, new Comparator<String>() {
          @Override
          public int compare(String a, String b) {
            return b.compareTo(a);
          }
        });
        
        // first iteration with lambda
        Collections.sort(names, (String a, String b) -> {
          return b.compareTo(a);
        });
        
        // now remove the data types and allow the compile to infer the type
        Collections.sort(names, (a, b) -> b.compareTo(a));
        
        /*
        Book {
         String title
         String authorFName
         String authorLName
         int pages
        }
        */
        Book book1 = new Book("Missing Peregrine", "Ranson", "Riggs", 382);
        Book book2 = new Book("Harry Potter", "JK", "Rowling", 411);
        Book book3 = new Book("The cat", "Dr", "Seuss", 45);
        
        List<Book> books = Arrays.asList(book1, book2, book3);
        int total = book.stream()
              .collect(Collectors.summingInt(Book::getPages));
        System.out.println(total); //838
        
        List<String> lilst = books.stream()
              .map(Book::getAuthorLName)
              .collect(Collectors.toList());
        System.out.println(list); // [Riggs, Rowling, Seuss]
        
        // create a list with duplicates
        List<Book> dupBooks = Arrays.asList(book1, book2, book3, book1, book2);
        System.out.println("Before removing dupliates");
        System.out.println(dupBooks.toString());
        
        // remove duoplicates using a Set
        Collection<Book> noDups = new HashSet<>(dupBooks);
        System.out.println("After removing dupliates");
        System.out.println(noDups.toString());
        
        // example of using Set to eliminate dups and sort automatically
        Set<Integer> numbers = new HashSet<>(asList(4,3,3,3,2,1,1,1));
        System.out.println(numbers.toString()); // [1,2,3,4]
      }
    }
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  • 原文地址:https://www.cnblogs.com/Answer1215/p/14209573.html
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