Java List排序4种写法整理

public static void main(String[] args)  {
        List<Integer> numList=new ArrayList<>();
        numList.add(999);
        numList.add(123);
        numList.add(456);
        numList.add(66);
        numList.add(9);
        Collections.sort(numList);  //使用Collections类的方法排序
        numList.sort(new Comparator<Integer>() {//使用List接口的方法排序
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1.compareTo(o2);
            }
        });
        //lambda表达式实现List接口sort方法排序
        numList.sort((num1,num2)->{return num1.compareTo(num2);});
        System.out.println(numList);
    }

public static void main(String[] args)  {
	List<User> numList=new ArrayList<>();
	User u=new User();
	u.setAge(12);
	numList.add(u);
	User u1=new User();
	u1.setAge(34);
	numList.add(u1);
	User u2=new User();
	u2.setAge(6);
	numList.add(u2);
	User u3=new User();
	u3.setAge(99);
	numList.add(u3);
	//Collections类的sort方法对对象集合排序，要传集合和Comparator接口两个参数
	Collections.sort(numList, new Comparator<User>() {
		@Override
		public int compare(User o1, User o2) {
			Integer age1= o1.getAge();
			Integer age2= o2.getAge();
			return  age1.compareTo(age2);
		}
	});
	//List接口自身的sort方法对对象集合排序，重写Comparator接口方法即可
	numList.sort(new Comparator<User>() {
		@Override
		public int compare(User u1, User u2) {
			Integer age1= u1.getAge();
			Integer age2= u2.getAge();
			return  age1.compareTo(age2);
		}
	});
	//List接口的sort方法，lambda表达式写法
   numList.sort((u4,u5)->{
		Integer age1= u4.getAge();
		Integer age2= u5.getAge();
		return  age1.compareTo(age2);
	});
	System.out.println(numList);
}

根据年龄倒序排
public static void main(String[] args)  {
	List<User> numList=new ArrayList<>();
	User u=new User();
	u.setAge(12);
	numList.add(u);
	User u1=new User();
	u1.setAge(34);
	numList.add(u1);
	User u2=new User();
	u2.setAge(6);
	numList.add(u2);
	User u3=new User();
	u3.setAge(99);
	numList.add(u3);
	numList = numList.stream().sorted(Comparator.comparing(User::getAge).reversed()).collect(Collectors.toList());
}

先对学生的班级做排序，然后同班级做倒序
public static void main(String[] args)  {
	List<User> numList=new ArrayList<>();
	User u=new User();
	u.setClass(1);
	u.setAge(12);
	numList.add(u);
	User u1=new User();
	u.setClass(1);
	u1.setAge(34);
	numList.add(u1);
	User u2=new User();
	u.setClass(2);
	u2.setAge(6);
	numList.add(u2);
	User u3=new User();
	u.setClass(2);
	u3.setAge(99);
	numList.add(u3);
	numList = numList.parallelStream().sorted(
	  Comparator.comparing(User::getClass).reversed().thenComparing(User::getAge)
	).collect(Collectors.toList());
}

public static void main(String[] args)  {
	List<User> numList=new ArrayList<>();
	User u=new User();
	u.setClass(1);
	u.setAge(12);
	numList.add(u);
	User u1=new User();
	u.setClass(1);
	u1.setAge(34);
	numList.add(u1);
	User u2=new User();
	u.setClass(2);
	u2.setAge(6);
	numList.add(u2);
	User u3=new User();
	u.setClass(2);
	u3.setAge(99);
	numList.add(u3);
	numList = numList.parallelStream().sorted(
	  Comparator.nullsFirst(User::getClass).reversed().thenComparing(User::getAge)
	).collect(Collectors.toList());
}