How to sort an array in reverse order using java?

Question

package javaLearning;
import java.util.Arrays;
import java.util.Collections;

    public class myarray {

         public static void name() {
         String hello;
         hello = "hello, world";
         int hello_len = hello.length();
         char[] hello_array = new char[hello_len];
         hello.getChars(0, hello_len, hello_array, 0);
         Arrays.sort(hello_array, Collections.reverseOrder());
}

the "myarray" class is defiend in a main method of a testing class. why does it give me a compile error when I try reversing the array?

Exception in thread "main" java.lang.RuntimeException: Uncompilable source code — Aaron
– Aaron, Commented Apr 7, 2011 at 16:47
since that apparently you're learning Java you should know that the official guidelines favors the use of all-lowercase package names. Prefer javalearning to javaLearning. — SyntaxT3rr0r
– SyntaxT3rr0r, Commented Apr 7, 2011 at 16:53

Aravindan R · Accepted Answer · 2011-04-07 17:19:13Z

6

Collections.reverseOrder() returns a Comparator<Object>. And Arrays.sort with comparator doesn't work for primitives

This should work

import java.util.Arrays;
import java.util.Collections;

public class MyArray {

    public static void name() {            
        String hello = "hello, world";
        char[] hello_array = hello.toCharArray();
        // copy to wrapper array
        Character[] hello_array1 = new Character[hello_array.length];
        for (int i = 0; i < hello_array.length; i++) {
           hello_array1[i] = hello_array[i];
        }
        // sort the wrapper array instead of primitives
        Arrays.sort(hello_array1, Collections.reverseOrder());                            
    }
}

edited Apr 7, 2011 at 17:19

answered Apr 7, 2011 at 16:59

Aravindan R

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Comments

Jeff Foster · Accepted Answer · 2011-04-07 16:47:59Z

2

The error I get (assuming the original post had some typos) is that Collections.reverseOrder() returns a Comparator<Object>.

Arrays.sort (with a compartor) is only defined for descendents of Object so doesn't work for primitive types.

answered Apr 7, 2011 at 16:47

Jeff Foster

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Comments

krookedking · Accepted Answer · 2011-04-07 16:46:49Z

0

You forgot to declare haa = hello.getChars(0, hello_len, hello_array, 0);

answered Apr 7, 2011 at 16:46

krookedking

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jtahlborn · Accepted Answer · 2011-04-07 17:19:00Z

0

Use Arrays.sort to sort in ascending order, then reverse the elements of the array (can be done inline with a simple loop).

answered Apr 7, 2011 at 17:19

jtahlborn

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Jagadeesh · Accepted Answer · 2012-08-22 13:03:16Z

0

The first thing is that the code is not followed the standards of JAVA language. Class name should always starts with UPPER case, and sort() of Arrays should not take primitive list of values as a parameter. change the 'char' to 'Character' and then use Arrays.sort method

answered Aug 22, 2012 at 13:03

Jagadeesh

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Comments

ewan.chalmers · Accepted Answer · 2011-04-07 16:46:49Z

-1

haa is not defined in the code you have shown us. That is a compile error.

answered Apr 7, 2011 at 16:46

ewan.chalmers

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1 Comment

Aaron Over a year ago

Ok, I have fixed the typo in the code and it is still giving me an error?

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