How to Compare Two Strings in Java

Comparing two strings in Java is a fundamental operation frequently used in various tasks, including input validation, data processing, and search algorithms. This article provides a comprehensive guide on different methods to compare strings in Java, along with illustrative examples.

Using the equals() Method

The most common and straightforward approach to compare strings in Java is using the equals() method. This method compares the content of two strings character by character, returning true if they are identical and false otherwise. Crucially, it is case-sensitive.

public class StringComparison {
    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = "hello";
        String str3 = "Hello";

        System.out.println(str1.equals(str2)); // Output: false
        System.out.println(str1.equals(str3)); // Output: true
    }
}

In this example, str1 and str2 are different because “H” and “h” have different Unicode values. str1 and str3 are equal as they have the same sequence of characters.

Other String Comparison Methods in Java

Beyond the equals() method, Java offers several other ways to compare strings:

1. equalsIgnoreCase() Method

For case-insensitive comparisons, the equalsIgnoreCase() method is ideal. It disregards the case of characters during comparison.

String str1 = "Hello";
String str2 = "hello";
System.out.println(str1.equalsIgnoreCase(str2)); // Output: true

2. compareTo() Method

The compareTo() method provides a lexicographical comparison of two strings. It returns:

0 if the strings are equal.
A negative value if the invoking string is lexicographically less than the argument string.
A positive value if the invoking string is lexicographically greater than the argument string.

String str1 = "Apple";
String str2 = "Banana";
System.out.println(str1.compareTo(str2)); // Output: a negative value

3. compareToIgnoreCase() Method

Similar to compareTo(), but performs a case-insensitive lexicographical comparison.

String str1 = "apple";
String str2 = "Banana";
System.out.println(str1.compareToIgnoreCase(str2)); // Output: a negative value

4. Objects.equals() Method

The Objects.equals(Object a, Object b) method handles null values gracefully. It returns true if both objects are null or if they are equal according to the equals() method. This helps avoid NullPointerExceptions.

String str1 = null;
String str2 = null;
System.out.println(Objects.equals(str1, str2)); // Output: true

Why not use == for String Comparison?

The == operator compares object references, not the actual string content. For strings, this can lead to incorrect results. Using equals() or its variants ensures content comparison.

String str1 = new String("Hello");
String str2 = new String("Hello");
System.out.println(str1 == str2); // Output: false
System.out.println(str1.equals(str2)); // Output: true

In this case, str1 and str2 refer to different objects in memory, even though their content is the same. Therefore == returns false, while equals() correctly returns true.

Conclusion

Choosing the right string comparison method depends on the specific requirements of your application. For simple content equality checks, equals() is sufficient. For case-insensitive comparisons, use equalsIgnoreCase(). For lexicographical ordering, use compareTo() or compareToIgnoreCase(). And to safely handle nulls, utilize Objects.equals(). Understanding these nuances ensures accurate and reliable string comparisons in your Java code.