How to sort a List<Object> in JAVA in the best way?

How-to-sort-a-List<Object>-in-JAVA?.md

How to sort a List<Object> in JAVA in a better way / the best way?

This is some notes written by Sheldon. I mainly focused on iOS programming but I also do JAVA and C# backend, you can find me with #iOSBySheldon in Github, Youtube, Facebook, etc.

High order functions with lambda is very easy in Swift (see article Here) but not that easy in languages like Objective-C or C++. In JAVA we can do it but since JAVA has too many versions, there are a lot different ways to do it, and there is always a better one you can choose.

Assuming we have a class like:

class Student {
    private int age;
    private String name;
    
    public Student(int age, String name) {
        this.age = age;
        this.name = name;
    }

    public int getAge() {
        return age;
    }
    public String getName() {
        return name;
    }
}

And we will have an list of Student to sort:

List<Student> list = new ArrayList<Student>();
list.add(new Student(33, "A"));
list.add(new Student(11, "C"));
list.add(new Student(22, "B"));

Sorting with Comparator

Comparator is the most classic one but also the one with the longest typing, basically we need to create a new Comparator for our sorting.

We can use Class function of Collection to sort:

Collections.sort(list, new Comparator<Student>() {
    @Override
	public int compare(Student o1, Student o2) {
        return o1.getAge().compareTo(o2.getAge());
    }
});

Or directly use list instance function to sort:

list.sort(new Comparator<Student>() {
	@Override
	public int compare(Student o1, Student o2) {
		return o2.getAge() - o1.getAge();
	}
});	

Sorting with Lambda

Lambda is a better and more concise way to replace Comparator for developers. (Similar in Swift)

//lambda
list.sort((Student o1, Student o2)->o1.getName().compareTo(o2.getName()));		
	
//lambda
list.sort((o1, o2)->o1.getAge().compareTo(o2.getAge()));

Sorting with Super Lambda Comparator

Note that for the first two ways, we are still comparing two things, but we can avoid comparing with:

list.sort(Comparator.comparing(o -> o.getName()));

Of course these are all sorting in the ascending order, if you need more complex condition to sort check the official document from Oracle Here.

:)

This is some notes written by Sheldon. I mainly focused on iOS programming but I also do JAVA and C# backend, you can find me with #iOSBySheldon in Github, Youtube, Facebook, etc.

With a method reference instead: list.sort(Comparator.comparing(Student::getName));.