public class ListDemo2 {
    public static void main(String[] args) {
        Student stu1 = new Student("01", "张三", 56);
        Student stu2 = new Student("02", "初夏", 45);
        Student stu3 = new Student("03", "易烊千玺", 23);
        Student stu4 = new Student("04", "王俊凯", 67);
        Student stu5 = new Student("05", "王一博", 58);

        List<Student> list = new ArrayList<Student>();
        list.add(stu1);
        list.add(stu2);
        list.add(stu3);
        list.add(stu4);
        list.add(stu5);

        System.out.println(list.toString());

        for (int i = 0; i < list.size(); i++) {
            Student stu = list.get(i);
            stu.setAge(18);
        }
        System.out.println(list.toString());
    }
}

运行结果如下：

[Student{sno='01', name='张三', age=56}, Student{sno='02', name='初夏', age=45}, Student{sno='03', name='易烊千玺', age=23}, Student{sno='04', name='王俊凯', age=67}, Student{sno='05', name='王一博', age=58}]
[Student{sno='01', name='张三', age=18}, Student{sno='02', name='初夏', age=18}, Student{sno='03', name='易烊千玺', age=18}, Student{sno='04', name='王俊凯', age=18}, Student{sno='05', name='王一博', age=18}]

以下循环 list，将集合中的stu对象的属性值age设置成18，为何不用新的集合去存更新age属性后的stu对象，而直接打印原list即可？

原因很简单：stu对象更新了，但它指向的内存地址没变，还是存放在原来的list中，所以打印原来的list即是更新属性值之后的对象。

// 1.排序，带参数类型
list.sort((String s1, String s2) -> s1.compareTo(s2));
list.sort(( LibraryDO lib1, LibraryDO lib2) -> lib2.getId().compareTo(lib2.getId()));
// 使用默认方法排序
Collections.sort(list, Comparator.comparing(LibraryDO::getId)); //升序
Collections.reverse(list); // 倒序排列
//随机打乱顺序
Collections.shuffle(list);
//更多排序
//默认ASC排序）
List<LibraryDO> collect = users.stream().sorted(Comparator.comparing(LibraryDO::getId)).collect(Collectors.toList());
//DESC排序）
List<LibraryDO> collect = users.stream().sorted(Comparator.comparing(LibraryDO::getId).reversed()).collect(Collectors.toList());

// 2.数组去重
List<String> collect = list.stream().distinct().collect(Collectors.toList());
// 数组去重转换为字符串
String joining = list.stream().distinct().collect(Collectors.joining(",")); 
// 根据对象属性去重
List<LibraryDO> lib = list.stream().collect(Collectors.collectingAndThen(
					Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(LibraryDO::getId))), ArrayList<LibraryDO>::new));

// 4.获取对象某一属性返回list
List<String> collect= list.stream().map(LibraryDO::getId).collect(Collectors.toList());
// 获取对象某一属性返回数组
Integer[] array = list.stream().map(LibraryDO::getId).collect(Collectors.toList()).stream().toArray(Integer[]::new);
// 获取对象某一属性返回数组过滤非空
Integer[] array = list.stream().map(LibraryDO::getId).filter(x -> x !=null).collect(Collectors.toList()).stream().toArray(Integer[]::new);
//5.修改对象属性值
List<LibraryDO> lib = list.stream().map(p -> {p.setId(p.getId() + 1);return p;}).collect(Collectors.toList())
/**
 * LibraryDO 对象
 */
public class LibraryDO implements Serializable {
	//ID
	private Integer id;
	//图书馆名称
	private String libName;
	//网址
	private String libUrl;
}

排序
https://www.cnblogs.com/woyaobianfei/p/9187127.htm