CODEWITHSUNDEEP
javasorting
cstur4
cstur4

Reputation: 1006

sort string by its length

 String[] arrays = {"AA", "B"};
 Arrays.sort(arrays, (s1, s2)->s1.length()-s2.length());
 System.out.println(Arrays.toString(arrays));

It's my test for jdk 8 environment. When s1.length() is bigger than s2.length(), the comparator return a negative number, thus s1 is in front of s2. But the result is ["B", "AA"]. What's wrong ?

When s1.length() is bigger than s2.length(), the comparator return a positive number, thus s2 is in front of s1. So the result is ["B", "AA"]. I just make a foolish mistake.

Upvotes: 0

Views: 816

Answers (3)

Karibasappa G C
Karibasappa G C

Reputation: 2732

o1 - object1 in your case s1
o2 - object2 in your case s2

compare method works and returns in this way

-1 : o1 < o2
0 : o1 == o2
+1 : o1 > o2

in your case s1 < s2 so it returns -1 and hence it sorts in ascending order smaller first and then bigger.

public int compare(String s1, String s2) {
        System.out.println(s1);
        System.out.println(s2);
        return s1.length() - s2.length();
    }

o/p

B
AA
[B, AA]

in below case if we reverse the return parameteres like below

public int compare(String s1, String s2) {
        System.out.println(s1);
        System.out.println(s2);
        return s2.length() - s1.length();
    }

it returns positive number hence sorts based on descending order bigger first and then smaller.

and the o/p is 

B
AA
[AA, B]

now return just 0

public int compare(String s1, String s2) {
        System.out.println(s1);
        System.out.println(s2);
        return s2.length() - s2.length();
    }

o/p - no sorting happened as it assumes all coming objects are equal.

B
AA
[AA, B]

let me know for any issues.

Upvotes: 2

Sotirios Delimanolis
Sotirios Delimanolis

Reputation: 279910

Let's modify it to log the values

String[] arrays = { "AA", "B" };
Arrays.sort(arrays, (s1, s2) -> {
    System.out.println("s1: " + s1);
    System.out.println("s2: " + s2);
    return s1.length() - s2.length();
});
System.out.println(Arrays.toString(arrays));

This prints

s1: B
s2: AA
[B, AA]

B has a smaller length than AA, so 

return s1.length() - s2.length();

returns a negative value. The sort method takes that and flips them in the array.

Upvotes: 1

Jeff Scott Brown
Jeff Scott Brown

Reputation: 27200

The logic is backward. It sounds like you want to subtract s1.length() from s2.length().

Upvotes: 0

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