String compareTo() Method in Java

String compareTo() Method in Java

Introduction: 

The compareTo() method in Java is used to compare two strings lexicographically. It returns an integer value that indicates the relationship between the two strings. This method is part of the String class and can be used to perform alphabetical comparisons.

Syntax:

java
public int compareTo(String anotherString)

Parameters:

• anotherString: The string to be compared with the current string.

Return Value:

• Returns an integer value that indicates the lexicographical comparison between the two strings.

• If the return value is less than 0: It means the current string is lexicographically less than the anotherString.

• If the return value is greater than 0: It means the current string is lexicographically greater than the anotherString.

• If the return value is equal to 0: It means the two strings are lexicographically equal.

Examples:

1. Basic Usage:

java
public class CompareToExample {
    public static void main(String[] args) {
        String str1 = "apple";
        String str2 = "banana";
        String str3 = "apple";

        int result1 = str1.compareTo(str2);
        System.out.println("Comparison Result 1: " + result1); // Output: Comparison Result 1: -1

        int result2 = str2.compareTo(str1);
        System.out.println("Comparison Result 2: " + result2); // Output: Comparison Result 2: 1

        int result3 = str1.compareTo(str3);
        System.out.println("Comparison Result 3: " + result3); // Output: Comparison Result 3: 0
    }
}

Explanation:

• In the first example, we compare "apple" with "banana". The result is -1 because 'a' (first character of "apple") comes before 'b' (first character of "banana") in the lexicographical order.
• In the second example, we compare "banana" with "apple". The result is 1 because 'b' (first character of "banana") comes after 'a' (first character of "apple") in the lexicographical order.
• In the third example, we compare "apple" with "apple". The result is 0 because both strings are identical, and their lexicographical order is the same.

2. Ignoring Case:

java
public class CompareToIgnoreCaseExample {
    public static void main(String[] args) {
        String str1 = "apple";
        String str2 = "Apple";

        int result = str1.compareToIgnoreCase(str2);
        System.out.println("Comparison Result: " + result); // Output: Comparison Result: 0
    }
}

Explanation:

• The compareToIgnoreCase() method is similar to compareTo(), but it ignores the case while performing the comparison. In this example, "apple" and "Apple" are considered equal, and the result is 0.

3. Using compareTo() with Sorted Collections:

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

public class SortedCollectionExample {
    public static void main(String[] args) {
        List<String> fruits = Arrays.asList("banana", "apple", "orange", "grape");
        Collections.sort(fruits);

        System.out.println("Sorted List: " + fruits);
        // Output: Sorted List: [apple, banana, grape, orange]
    }
}

Explanation:

• In this example, we use the compareTo() method indirectly to sort a list of fruits in lexicographical order. The Collections.sort() method internally uses compareTo() to compare the elements and sort them accordingly.

Note:

• When using the compareTo() method, ensure that the strings being compared are not null, as it may result in a NullPointerException. To handle such cases, it's recommended to perform null checks or use the Objects.compare() method available from Java 7 onwards.

This concludes the documentation on the compareTo() method in Java. It allows you to compare strings based on their lexicographical order, which is useful for sorting and ordering operations.