Often, it is not enough to simply know whether two strings are identical. For sorting applications, you need to know which is less than, equal to, or greater than the next. A string is less than another if it comes before the other in dictionary order. A string is greater than another if it comes after the other in dictionary order. The String method compareTo( ) serves this purpose. It has this general form:

int compareTo(String str)

Here, str is the String being compared with the invoking String. The result of the comparison is returned and is interpreted as shown here:

Value                                    Meaning
Less than zero                     The invoking string is less than str.

Here is a sample program that sorts an array of strings. The program uses compareTo( ) to determine sort ordering for a bubble sort:

// A bubble sort for Strings.
class SortString {
static String arr[] = {
"Now", "is", "the", "time", "for", "all", "good", "men",
"to", "come", "to", "the", "aid", "of", "their", "country"
};

public static void main(String args[]) {
for(int j = 0; j < arr.length; j++) {
for(int i = j + 1; i < arr.length; i++) {
if(arr[i].compareTo(arr[j]) < 0) {
String t = arr[j];
arr[j] = arr[i];
arr[i] = t;
}
}
System.out.println(arr[j]);
}
}
}

The output of this program is the list of words:

Now
aid
all
come
country
for
good
is
men
of
the
the
their
time
to
to

As you can see from the output of this example, compareTo( ) takes into account uppercase and lowercase letters. The word "Now" came out before all the others because it begins with an uppercase letter, which means it has a lower value in the ASCII character set.

If you want to ignore case differences when comparing two strings, use compareToIgnoreCase( ), shown here:

int compareToIgnoreCase(String str)

This method returns the same results as compareTo( ), except that case differences are ignored. This method was added by Java 2. You might want to try substituting it into the previous program. After doing so, "Now" will no longer be first.

2007-09-02

Comments(8)

1.	how i can used inheritence ? By: samee at 2008-02-16 12:54:27
2.	Hi you can find inheritance example in Java in the following tutorial. http://www.java-samples.com/showtutorial.php?tutorialid=658 By: Mashoud at 2008-04-26 20:12:37
3.	Superb many thanks to you Mashoud. i'm trying to learn Java in CNAM France and this code saved me 3 hours i was trying to class String arg ..... you saved me me.... By: orchidouest at 2009-05-10 12:58:53
4.	know someone how to compare various objects? I would like to have only one comparator for object like String, Long, Date... but these objects come as "Object"s any help? By: Peter at 2009-10-07 07:32:31
5.	Example: String sOne = "hello there"; String sTwo = "hallo there"; What would my output be in this situation? out.print(sOne.compareTo(sTwo)); and in this situation... out.print(sTwo.compareTo(sOne)); By: Adam at 2009-11-10 12:55:51
6.	@Adam: CompareTo returns the difference of the ASCII codes of the first non-matching character. So, out.print(sOne.compareTo(sTwo)); would display // (sTwo - sOne) ('a' - 'e') which is -4. and out.print(sTwo.compareTo(sOne)) would display //(sOne - sTwo) ('e' - 'a') which is 4. Hope this will help you. By: Azher at 2010-01-29 12:23:39
7.	hi, Very nice tutorial. But please I have some problems with this function. here is my problem: I have created a dictionary that uses text files as database. The text files are encoded in UTF-8 format. I read them with InputStreamReader(is, "UTF-8"); and save them in an array of string. Nothing problem till here. But the problem will start when I want to compare individual elements with the text I want. The loop passes through the correct one but using String.compareTo() will not stop it. I have used different methods to decode both texts but nothing worked. Any help will be appreciated. By: hemn at 2010-04-17 06:02:00
8.	You talk about "dictionary order". How would you sort the strings "item 11", "item 5"? By: Magnus A at 2010-08-31 22:58:06

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