Sorting ArrayList in Java

Question

I have a class (that implement Comparable) composed by:

double[1][2];

I would sorting my arrayList and i tried in this way but i reported an error:

public double compareTo(Matrix another) {
return this.getCell(0,1).compareTo(another.getCel(0,1));
} 

How can sorting in this way?

Answer 1

Presumably, the call to getCell() returns a double, which doesn't have methods (like (compareTo()).

Also, the compareTo() method of the Compareae interface must return int, not double.

Try this:

public int compareTo(Matrix another) {
    double diff = getCell(0,1) - another.getCel(0,1);
    return diff == 0 ? 0 : diff > 0 ? 1 : -1;
}

This solution will work in all java versions. For java 7+, you may do thus instead:

public int compareTo(Matrix another) {
    return Double.compare(getCell(0, 1), another.getCell(0, 1));
} 

Also note the slight clean up of removing the redundant this. from your code.