Sorting strings in java?

[alexander.s]

Hi all,

I'd like to know how to sort strings in java. Usually in C I'd do something like this:

for(i=0;i<length-1;i++)
{
          for(j=0;j<length;j++)
          {
                   if(strcmp(name[i],name[j])>0)
                   {
                             strcpy(tmp,name[i]);
                             strcpy(name[i],name[j]);
                             strcpy(name[j],tmp);
                   }
          }
}

I'd love to be able to do the same thing in Java, thanks in advance!

[Eranga]

Store them in a TreeSet, it ordered all elements in natural order. Or use Array.sort() on a string array.

[Eranga]

Here is a simple example.

/**
 *
 * @author Eranga Tennakoon
 */
public class SortArrays {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
        String[] arr = new String[]{"Java", "Forums", "Sun", "Apache",
        "JSP", "AJAX", "XML"};
        new SortArrays().sortStrings(arr);
    }

    private void sortStrings(String[] arr) {
        java.util.Arrays.sort(arr);
        for(int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }
    }
}

[Norm]

The code in java would be translated one for one line of code.
There are comparable methods to the C strcmp function in the String class. Java is a bit more wordy. Read the API doc for String.
Use assignment statement vs using strcpy for the rest

[fishtoprecords]

Store them in any Collection implementation that has a "sort()" member function, and call it.

[Eranga]

In a TreeSet it's automatically happens, right?

[fishtoprecords]

In a TreeSet it's automatically happens, right?

I think so, I'd have to check the javadocs. But you may need a comparitor of you want to support sorting in a special way.

So the general answer is use a Collection, and a TreeSet is one.

I don't know any of the asian languages, but even European ones have some non-obvious rules. For example, in Spanish, the "ch" pair is sorted as if it was a single character and sorts after "C" alone.

Doing "strings" properly in a multi-language environment is a bit of a challenge. Java lets you do it "right" but its not all automatic.

[Eranga]

Yep you are right? If we think in English-only mindset sorting strings is easy. But in different languages, it wont.

In TreeSet internally elements are sorted in natural order, and output as an array. See the example bellow.

    public static void main(String[] args) {
        TreeSet at = new TreeSet();
        at.add("Java");
        at.add("Name");
        at.add("NetBeans");
        at.add("AJAX");
        
        System.out.println(at);
    }

As you said, generally it comes from Java Collection framework, but specifically TreeSet. :)

[serjant]

For different languages,other than English, we i think we should write a unicode convert function,and then creating unicode strings in TreeSet,maybe then it will sort.I will try to make a little test application now in Eclipse with Russian and Hebrew languages .

[serjant]

I checked the TreeSet sorts the array only for English characters,for german with umlauts it sends the strings to the end of the TreeSet,in hebrew it doesn't sort it at all and the same in Russian,but the Arrays.sort(<some array of strings>) sorts everything,that means TreeSet doesn't support unicode while sorting.
So in TreeSet the strings in other languages should be unicoded first and then sorted with Comparator

import java.util.*;
public class JavaUnicode {
	private TreeSet set=new TreeSet();

	public JavaUnicode(){
		
		set.add("דויד");
		set.add("קריש");
		set.add("גרושה");
		set.add("אלמן");
		
		System.out.println(set);
		
		
		String[] s=new String[]{"דויד","קריש","גרושה","אלמן"};
		//String[] s=new String[]{"David","Allan","Nick"};
		
		Arrays.sort(s);
		for(int i=0;i<s.length;i++){
			System.out.println(s[i]);
		}
		
	}
	
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		new JavaUnicode();

	}

}

the output:

[אלמן, גרושה, דויד, קריש]
אלמן
גרושה
דויד
קריש

[Eranga]

So the java.util.Arrays.sort() is the best choice in sorting. It's easy to work on, because no need to deal with UNICODE conversions and so on.