Java OCA OCP Practice Question 1577

Question

Suppose we want to implement a Comparator<String> so that it sorts the longest strings first.

You may assume there are no nulls. Which method could implement such a comparator? 

A.   public int compare(String s1, String s2) {
        return s1.length() - s2.length();
     }/*from   w w  w .j  av a2  s  .c o  m*/

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

C.   public int compare(Object obj1, object obj2) {
        String s1 = (String) obj1;
        String s2 = (String) obj2;
        return s1.length() - s2.length();
     }

D.   public int compare(Object obj1, object obj2) {
        String s1 = (String) obj1;
        String s2 = (String) obj2;
        return s2.length() - s1.length();
     }



B.

Note

Options C and D are incorrect because the method signature is incorrect.

Unlike the equals() method, the method in Comparator takes the type being compared as the parameters when using generics.

Option A is a valid Comparator.

However, it sorts in ascending order by length.

Option B is correct.

If s1 is three characters and s2 is one character, it returns -2.

The negative value says that s1 should sort first, which is correct, because we want the longest String first.




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