String Comparison in Java: A Comprehensive Guide

Java provides several ways to compare strings, each with its own strengths and weaknesses. The best method depends on whether you need a case-sensitive comparison, are checking for equality, or need to determine the lexicographical order. This guide clarifies the most common approaches.

Table of Contents

1. Using the compareTo() Method
2. The == Operator
3. The equals() Method
4. Case Sensitivity and equalsIgnoreCase()
5. The contentEquals() Method

1. Comparing Strings with compareTo()

The compareTo() method offers a lexicographical comparison. It returns:

• 0: If the strings are equal.
• A negative value: If the invoking string precedes the argument string lexicographically.
• A positive value: If the invoking string follows the argument string lexicographically.

This comparison is case-sensitive; uppercase letters precede lowercase letters.

String str1 = "apple";
String str2 = "banana";
String str3 = "Apple";

int result1 = str1.compareTo(str2); // result1 will be negative
int result2 = str1.compareTo(str3); // result2 will be negative (case-sensitive)
int result3 = str1.compareTo("apple"); // result3 will be 0

2. The == Operator

The == operator compares references, not string content. It checks if two string variables point to the same memory location. This is usually not the desired behavior for comparing string values.

String str1 = "hello";
String str2 = "hello";
String str3 = new String("hello");

System.out.println(str1 == str2); // Often true due to string interning
System.out.println(str1 == str3); // false (different objects)

While str1 == str2 often returns true because of Java’s string interning, relying on this is unreliable. Always use equals() for content comparison.

3. The equals() Method

The equals() method is the recommended approach for comparing string content. It compares characters, disregarding memory locations.

String str1 = "hello";
String str2 = "hello";
String str3 = new String("hello");

System.out.println(str1.equals(str2)); // true
System.out.println(str1.equals(str3)); // true

4. Case Sensitivity and equalsIgnoreCase()

equals() is case-sensitive. “hello” and “Hello” are considered different. For case-insensitive comparisons, use equalsIgnoreCase().

String str1 = "hello";
String str2 = "Hello";

System.out.println(str1.equals(str2)); // false
System.out.println(str1.equalsIgnoreCase(str2)); // true

5. The contentEquals() Method

contentEquals() is similar to equals(), but it allows comparing a String with other CharSequence objects (like StringBuffer or StringBuilder).

String str1 = "hello";
StringBuffer str2 = new StringBuffer("hello");

System.out.println(str1.contentEquals(str2)); // true

This offers flexibility, but for simple string-to-string comparisons, equals() is preferred for readability.

In summary, select the appropriate method based on your needs: compareTo() for lexicographical order, equals() for case-sensitive content equality, equalsIgnoreCase() for case-insensitive equality, and contentEquals() for comparing strings with other CharSequence objects. Avoid using == for comparing string content.