獲取list<Entity>中某個屬性組成新的集合

• 按以往常用的方式

  Person p1 = new Person();
  p1.setName("張三");
  p1.setAge(20);
  Person p2 = new Person();
  p2.setName("李四");
  p2.setAge(18);
  
  List<Person> personList = new ArrayList<>(2);
  personList.add(p1);
  personList.add(p2);
  
  List<String> names = new ArrayList<>(personList.size());
  for (Person person : personList) {
      names.add(person.getName());
  }
  System.out.println(names);
  

  以上這種方式動不動就搞個循環(huán)撮弧，數(shù)據(jù)量大點就會出大事巩搏，輕的造成卡頓鞭光，嚴重的就Game Over了 匀奏，好在Java8 List Stream解決了這個問題

• Java8 list stream方式

  List<String> names = personList.stream().map(Person::getName).collect(toList());
  System.out.println(names);
  

  這種方式是不是簡單到爆炸普气，這些只是stream應用的一部分栏渺，下面為大家提供一些應用demo

• Java8 list stream demo

  List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
  List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
  System.out.println("列表: " +strings);
  
  long count = strings.stream().filter(String::isEmpty).count();
  System.out.println("空字符串數(shù)量為: " + count);
  
  count = strings.stream().filter(string -> string.length() == 3).count();
  System.out.println("字符串長度為 3 的數(shù)量為: " + count);
  
  List<String> filtered = strings.stream().filter(string -> !string.isEmpty()).collect(toList());
  System.out.println("篩選后的列表: " + filtered);
  
  String mergedString = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.joining(", "));
  System.out.println("合并字符串: " + mergedString);
  
  List<Integer> integers = Arrays.asList(1,2,13,4,15,6,17,8,19);
  List<Integer> squaresList = numbers.stream().map( i ->i*i).distinct().collect(Collectors.toList());
  System.out.println("Squares List: " + squaresList);
  System.out.println("列表: " +integers);
  
  IntSummaryStatistics stats = integers.stream().mapToInt((x) ->x).summaryStatistics();
  
  System.out.println("列表中最大的數(shù) : " + stats.getMax());
  System.out.println("列表中最小的數(shù) : " + stats.getMin());
  System.out.println("所有數(shù)之和 : " + stats.getSum());
  System.out.println("平均數(shù) : " + stats.getAverage());
  System.out.println("隨機數(shù): ");
  
  Random random = new Random();
  random.ints().limit(10).sorted().forEach(System.out::println);
  
  // 并行處理
  count = strings.parallelStream().filter(String::isEmpty).count();
  System.out.println("空字符串的數(shù)量為: " + count);