TreeMap.java

//Student mark class
class StudentMark implements Comparable<StudentMark>{
	int mark;
	StudentMark(int mark) {
		this.mark = mark;
	}
	@Override
	public String toString() {
		return "Student [mark=" + mark + "]";
	}
	@Override
	public int compareTo(StudentMark o) {
		if (o.mark > this.mark) return 1;
		else if (o.mark == this.mark) return 0;
		else return -1;
	}
}

//TreeMap
StudentMark s1 = new StudentMark(10);
		StudentMark s2 = new StudentMark(5);
		StudentMark s3 = new StudentMark(6);
		StudentMark s4 = new StudentMark(9);
		
		TreeMap<StudentMark, String> array = new TreeMap<StudentMark, String>();
		array.put(s1, "John");
		array.put(s2, "Daniel");
		array.put(s3, "Joseph");
		array.put(s4, "Mark");
		
		for (Entry<StudentMark, String> entry : array.entrySet()) {
			System.out.println(entry.getKey() + " - " + entry.getValue());
		}
		
//OUTPUT
//Student [mark=10] - John
//Student [mark=9] - Mark
//Student [mark=6] - Joseph
//Student [mark=5] - Daniel