Comparator and compare method

Question

Help to understand the logic of the program. We have 3 arrays of strings, they are written in ArrayList, I sort them by the number of elements in the sheet. What I can not understand: how is this sorting done? What's going on here?

Comparator<String[]> sortByLength = new Comparator<String[]>() { @Override public int compare(String[] o1, String[] o2) { return o1.length - o2.length; } };

 public class T{ public static void main(String[] args) { String[] array1 = {"мама", "мыла", "раму"}; String[] array2 = {"я", "очень", "люблю", "java"}; String[] array3 = {"мир", "труд", "май"}; List<String[]> arrays = new ArrayList<>(); arrays.add(array1); arrays.add(array2); arrays.add(array3); Comparator<String[]> sortByLength = new Comparator<String[]>() { @Override public int compare(String[] o1, String[] o2) { return o1.length - o2.length; } }; arrays.sort(sortByLength); for (String[] str : arrays) { System.out.println(Arrays.toString(str)); } } }

Accepted Answer · 2019-04-17T11:47:20

Sorting takes place here arrays.sort(sortByLength);
arrays is your ArrayList object. It has a sort method to which to sort you pass an object that implements the Comparator interface.

In this code block

 Comparator<String[]> sortByLength = new Comparator<String[]>() { @Override public int compare(String[] o1, String[] o2) { return o1.length - o2.length; } };

You implement an anonymous class using the Comparator interface. It has a compare method that accepts two objects and returns for sorting.
0 : if objects are equal
-1 (not necessarily -1, there must be any negative number): if o1 <o2
1 (any positive number): if o1> o2

UDP This code is old. up to Java 8. In Java 8, there appeared the Lamba functions that give more elegant code, like this:

 arrays.sort((o1, o2) -> o1.length - o2.length); /// или arrays.sort(Comparator.comparingInt(o -> o.length));

Could you please tell me how the arrays of strings are passed to the compare method, I mean, there are only two parameters (String [] o1, String [] o2), how are all the elements of the list being sorted out then?
@Makaroni if IDEA clicks on the sort method, then you can see its implementation.

Dred dred 923 3 18 · Answer 2 · 2019-04-17T11:46:11

The comparator compares the current value and the following. That is, you will compare something like this

 {"я", "очень", "люблю", "java"} > {"мама", "мыла", "раму"} = 1 {"мир", "труд", "май"} < {"я", "очень", "люблю", "java"} = -1 {"мир", "труд", "май"} < {"я", "очень", "люблю", "java"} = 1 {"мама", "мыла", "раму"} < {"мир", "труд", "май"} = 0

Based on these values, the comporator will put in ascending order depending on the length of the array.

 [мама, мыла, раму] [мир, труд, май] [я, очень, люблю, java]

No need to lie about the "current value and the following ."
You might think that the comparator goes through the array and compares 2 neighboring elements
@AndrewBystrov and how then does a walk through all the arrays take place?

Comparator and compare method

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