Stream的排序

1、list<Integer>的正序

List<Integer> list = new ArrayList<>();
list.add(50);
list.add(45);
list.add(25);
list.add(98);
list.add(32);
List<Integer> collect = list.stream().sorted().collect(Collectors.toList());
System.out.println("list<Integer>元素正序：" + collect);


打印結果：
list<Integer>元素正序：[25, 32, 45, 50, 98]

2、list<Integer>的倒序

List<Integer> list = new ArrayList<>();
list.add(50);
list.add(45);
list.add(45);
list.add(98);
list.add(32);
List<Integer> collect = list.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
System.out.println("list<Integer>元素倒序：" + collect);

打印結果：
list<Integer>元素倒序：[98, 50, 45, 45, 32]

3、List<Person>的元素的屬性值正序

Person p1 = new Person("張三", new BigDecimal("50.0"));
Person p2 = new Person("王五", new BigDecimal("25.0"));
Person p3 = new Person("李四", new BigDecimal("68.0"));
Person p4 = new Person("李四", new BigDecimal("17.0"));
Person p5 = new Person("張三", new BigDecimal("45.0"));
List<Person> list = new ArrayList<>();
list.add(p1);
list.add(p2);
list.add(p3);
list.add(p4);
list.add(p5);
list.sort(Comparator.comparing(person -> person.getSalary()));
System.out.println(list);

打印結果：
元素的屬性值正序：[{name='李四', salary=17.0}, {name='王五', salary=25.0}, {name='張三', salary=45.0}, {name='張三', salary=50.0}, {name='李四', salary=68.0}]

4、List<Person>的元素的屬性值倒序

Person p1 = new Person("張三", new BigDecimal("50.0"));
Person p2 = new Person("王五", new BigDecimal("25.0"));
Person p3 = new Person("李四", new BigDecimal("68.0"));
Person p4 = new Person("李四", new BigDecimal("17.0"));
Person p5 = new Person("張三", new BigDecimal("45.0"));
List<Person> list = new ArrayList<>();
list.add(p1);
list.add(p2);
list.add(p3);
list.add(p4);
list.add(p5);
List<Person> collect = list.stream().sorted(Comparator.comparing(Person::getSalary).reversed()).collect(Collectors.toList());
System.out.println("元素的屬性值倒序：" + collect);

打印結果：
元素的屬性值倒序：[{name='李四', salary=68.0}, {name='張三', salary=50.0}, {name='王五', salary=45.0}, {name='張三', salary=45.0}, {name='李四', salary=17.0}]

 

// 按年齡排序(正序)
list.sort(Comparator.comparing(item->(int)item.get(age)))
// 將list中的元素反轉（正序+反轉=倒序）
Collections.reverse(list)
// 此時list 按age字段倒排