new to java - how to write compareTo method for sorting
android, java, sorting
Solution
It all depends on how the interface `Comparable` is implemented.
If in the class you see
implements Comparable
then the first `compareTo` method is correct. This was the way to implement `Comparable` through Java 1.4, the last version before generics was introduced. It's implementing the raw interface `Comparable` (without any generics).
If in the class you see
implements Comparable<Student1>
then the second `compareTo` method is correct. Generics helps in this case by supplying the type of the parameter in the `compareTo` method.
Both are right, but the first one is obsolete and the second one is now favored.
- `Comparable` javadocs
- Java generics tutorial
Problem
I have been going through some tutorials on how to sort an object based on one if its properties. For example, if we have a class called person which has a property called name, we simply implement Comparable interface and override compareTo. However, different tutorials show different code which you write inside compareTo, for example here is one way: ``` public int compareTo(Object o) throws ClassCastException { Date d = (Date)o; // If this doesn't work, ClassCastException is thrown int yd = year - d.year; int md = month - d.month; int dd = day - d.day; if (yd != 0) return yd; else if (md != 0) return md; else return dd; ``` } but yet here is different way to write the compareTo method: ``` @Override public int compareTo(Student1 o) { return Integer.compare(grade, o.grade); } ``` as a result I am totally confused as to what algorithm or formula is required to write a proper compareTo