We can sort list using multiple fields with Comparator. Here we are going to see two ways to do that.

Let’s say we have a Student class as below.

public class Student{
private int rollNum;
private String firstName;
private String stream;

public Student(int rollNum, String firstName, String stream) {
    super();
    this.rollNum = rollNum;
    this.firstName = firstName;
    this.stream = stream;
}

public String getFirstName() {
    return firstName;
}
public void setFirstName(String firstName) {
    this.firstName = firstName;
}
public int getRollNum() {
    return rollNum;
}
public void setRollNum(int rollNum) {
    this.rollNum = rollNum;
}
public String getStream() {
    return stream;
}
public void setStream(String stream) {
    this.stream = stream;
}

@Override
public String toString() {
    return stream +" " +firstName +" "+ rollNum;
}
}

And a list of Students.

	private List<Student> getStudentList() {
		return Arrays.asList(new Student(1, "Bindu", "IT"), 
new Student(2, "Sam", "CS"),
 new Student(3, "David", "IT"),
new Student(4, "Anjali", "CS"));
	}

We can compare the list using multiple fields using two methods as below:

1. Using anonymous class

We need to make use of Comparator interface to compare using multiple fields. Comparator is a functional interface, which mean it has only one abstract method compare. We are going to override this method in anonymous class.

private List<Student> sortWithAnymClass(List<Student> list) {
		Collections.sort(list, new Comparator<Student>() {
			// compare using stream and then rollNumber;
			@Override
			public int compare(Student s1, Student s2) {
				if (s1.getStream().equals(s2.getStream())) {
					if (s1.getRollNum() == s2.getRollNum())
						return 0;
					if (s1.getRollNum() > s2.getRollNum())
						return 1;
					return -1;
				}
				return s1.getStream().compareTo(s2.getStream());
			}
		});

		return list;
	}

2. Using lambda expression

private List<Student> sortWithLambdaExp(List<Student> list) {
		// sort using stream and firstName
		list.sort(Comparator.comparing((Student s) -> s.getStream()).thenComparing((Student s) -> s.getFirstName()));
		return list;

	}

Sharing is caring!