Sort an array of objects in java?

Question

public class WordArray {
        public char[] str;
        public int[] index;
}

This is a class which stores words in the character array str

public class DuplicateArray {
    WordArray wordArray[];
    int size;

    public static DuplicateArray getDupArray(int size , String string[]){
        DuplicateArray da = new  DuplicateArray();
        da.size = size;
        da.wordArray = new WordArray[da.size];
        for (int i = 0; i < da.size; i++) {
            da.wordArray[i] = new WordArray();
            da.wordArray[i].str = new char[string[i].length()];
            da.wordArray[i].index = new int[da.size];
            da.wordArray[i].str = string[i].toCharArray();
            da.wordArray[i].index[i] = i;       
        }
        return da;

    }
}

This class uses the WordArray class and copies the individual words from the String array string to the character str array in each wordArray[i].

First I want to sort the individual characters that are stored in the str's of each wordArray.

Then I want to sort the each word in the wordArray but I want to retain the original indexes of the words in string for later use. For that I am using this class:

public class PrintAnagram {

    public static void printAnagram(String[] string) {
        DuplicateArray da = DuplicateArray.getDupArray(string.length, string);

        for (int i = 0; i < string.length; i++) {
            Arrays.sort(da.wordArray[i].str);
        }
        Arrays.sort(da.wordArray);

        for (int i = 0; i < string.length; i++){
            System.out.println(string[da.wordArray[i].index[i]]);
        }

    }

}

But Class caste exceptions occurs in ComparableTimsort or something , about which , I have no idea. From what I have read in previous question , we have to override the compareTo. But I don't know where to override it, Should I overide it in PrintAnagramclass , where I am actually sorting or should I override it in WordArray or in DuplicateArray . If anyone has the time to explain this stuff then please or you can point me to some resource where all this is clearly explained. I am fairly new to Java.

Exceptions :

Exception in thread "main" java.lang.ClassCastException: self.study.WordArray cannot be cast to java.lang.Comparable
    at java.util.ComparableTimSort.countRunAndMakeAscending(ComparableTimSort.java:290)
    at java.util.ComparableTimSort.sort(ComparableTimSort.java:157)
    at java.util.ComparableTimSort.sort(ComparableTimSort.java:146)
    at java.util.Arrays.sort(Arrays.java:472)
    at self.study.PrintAnagram.printAnagram(PrintAnagram.java:13)
    at self.study.AnagramTogether.main(AnagramTogether.java:7)

You should take a look at http://stackoverflow.com/questions/683041/java-how-do-i-use-a-priorityqueue — Joren, Aug 24 '13 at 13:46
You'd override compareTo in WordArray. It would have to know how to compare itself to another WordArray and determine which was "larger", etc. — Hot Licks, Aug 24 '13 at 13:50
Quoting `Arrays.sort`'s documentation: Sorts the specified array of objects into ascending order, according to the natural ordering of its elements. **All elements in the array must implement the Comparable interface**. Furthermore, all elements in the array must be mutually comparable (that is, e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the array). — Giulio Franco, Aug 24 '13 at 13:50
Why don't you use some sort of collections, if sorting is the prime factor? — Lion, Aug 24 '13 at 13:52

Sazzadur Rahaman · Accepted Answer · 2013-08-24T13:56:31.007

2

Your class WordArray should implement the interface Comparable to be sorted using Arrays.sort function.

So the signature of the WordArray should be like:

public class WordArray implements Comparable<WordArray>

and the class should implement the method :

public int compareTo(WordArray compareWordArray)

Or you should provide an explicit implementation of Comparator interface to sort method.

For details see this.

edited Aug 24 '13 at 13:56

answered Aug 24 '13 at 13:50

Sazzadur Rahaman

6,938
1
30
52

score 2 · Answer 2 · answered Aug 24 '13 at 13:54

2

just as @Rahaman says.

Or you can define a comparator as the second parameter.

Arrays.sort(da.wordArray, comparator);

answered Aug 24 '13 at 13:54

Loki

931
8
13

Sort an array of objects in java?

2 Answers2