Sorting a String using java collections

Question

I am attaching following code and i want to sort this as

 class sort{
    public static void main(String args[])  
    {String a ="this is a kiran";  
    StringTokenizer st =new StringTokenizer(a);  
    List f=new ArrayList();  
    f.add(st);  
    Collections.sort(f);  
    System.out.println("after sortting "+f);  
    }
 }

I want output as:

a
is 
kiran 
this

But i am getting an exception as:-
Exception in thread "main" java.lang.ClassCastException: java.util.StringTokenizer cannot be cast to java.lang.Comparableat java.util.Collections.sort(UnknownSource)atcom.sort.main(Sort.java:18)

why not use string.split("\\s+") instead of String tokenizer? — TheLostMind
– TheLostMind, Commented Jan 21, 2014 at 14:17
You can't just add the StringTokenizer to your list. Use the StringTokenizer to iterate through the tokens. — Teresa Carrigan
– Teresa Carrigan, Commented Jan 21, 2014 at 14:18
The StringTokenizer class does not implement the Comparable interface. "All elements in the list must implement the Comparable interface. Furthermore, all elements in the list must be mutually comparable (that is, e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the list)." — Alexis C.
– Alexis C., Commented Jan 21, 2014 at 14:18

Ruchira Gayan Ranaweera · Accepted Answer · 2014-01-21 14:25:59Z

4

Change your code. There are some mistakes you need to correct.

    String a ="this is a kiran";
    StringTokenizer st =new StringTokenizer(a);
    List<String> f=new ArrayList<>(); // use String type list
    while (st.hasMoreTokens()){ // add all tokens by iterating st
        f.add(st.nextToken()); // add tokens to list
    }
    Collections.sort(f);
    System.out.println("after sorting "+f);

Out put:

   after sorting [a, is, kiran, this]

Now you are getting sorted list

edited Jan 21, 2014 at 14:25

answered Jan 21, 2014 at 14:18

Ruchira Gayan Ranaweera

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Comments

Sergey Kalinichenko · Accepted Answer · 2014-01-21 14:18:04Z

2

The problem is here:

f.add(st);

You are adding StringTokenizer to the list, instead of adding the individual tokens. Changing the code to use generics would have helped: if you declare your List as List<String>, the code wouldn't compile, pointing you in the right direction:

List<String> f=new ArrayList<String>();

Add a while loop to collect tokens from st, and add them to f one by one.

P.S. Since this is almost certainly a learning exercise, I am not going to spoil the fun for you by completing your code.

answered Jan 21, 2014 at 14:18

Sergey Kalinichenko

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Suganthan Madhavan Pillai · Accepted Answer · 2014-01-21 14:27:01Z

1

You can also use hasMoreElements() and nextElement()

class sort{
   public static void main(String args[])  {
       String a ="this is a kiran";
        StringTokenizer st =new StringTokenizer(a);
        ArrayList<String> f=new ArrayList<String>(); // use String type list
        while (st.hasMoreElements()){ // add all by iterating st
        f.add((String) st.nextElement()); // add tokens to list
    }
    Collections.sort(f);
    System.out.println("after sorting "+f);
    }
 }

answered Jan 21, 2014 at 14:27

Suganthan Madhavan Pillai

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DwB · Accepted Answer · 2014-01-21 14:37:42Z

0

Consider using String.split() to split your string. Class names should be nouns, method names should be verbs or verb phrases, and you should use generics.

public static void main(String[] arguments)
{
    String input = "this is hootberry sause";  
    String[] inputArray;
    List<String> inputList = new ArrayList<String>();

    inputArray = input.split(" ");
    Collections.addAll(inputList, inputArray);
    Collections.sort(inputList);

    System.out.println("Before sort: " + input);
    System.out.println("After sort: " + inputList);
}

answered Jan 21, 2014 at 14:37

DwB

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