how does compareTo and compare work?

Question

I know that compare and compareTo returns an int value.

For example:

Returns 0 if a equal b -1 if a < b +1 if a > b 

sort method makes a call to either compareTo or compare() methods. But how does sort method arranges the list when compare or compareTo returns a int value. What is background scenario running after a compare or compareTo returns an int value to sort?how does sort method makes use of int values(-1 or 0 or 1) returned to it from compare and compareTo

Answer 1

If the two elements (a,b) being compared are already in the right order, compare(a, b) and a.compareTo(b) both return a value that is <= 0, so nothing has to happen.

If they aren't in the right order, the return value is > 0, indicating that they must be interchanged.

Answer 2

General case sorting algorithms are based on comparisons. If you compare between a and b - there are exactly 3 possibilities: a == b, a > b, a < b.

The compare() or compareTo() method provides exactly this information.

Now, to use this information we have designed numerous sorting algorithms, starting with naive bubble sort, and some are more advances such as quick sort. Each providing a bit different approach to the sorting problem.

Java chose the TimSort algorithm for its sorting implementation.

As an exercise, you can design your own¹ sorting algorithm. Can you find the maximum element of an array using the compare() method? when you found it where should it be? what should you do next?

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(1) Well, think of it by yourself, but it already exists, actually :)