Comparing strings by their alphabetical order

java

prompt-engineering

best-practices

functions

byNikita Barsukov·Feb 2, 2025

In Java, you compare strings alphabetically using the compareTo method. This sorts the strings lexicographically, or case-sensitive where uppercase letters precede lowercase.

String a = "apple";
String b = "banana";
// Who knew apples could beat bananas in something? 😉
System.out.println(a.compareTo(b));

For case-insensitive comparisons, you should use compareToIgnoreCase.

String a = "apple";
String b = "Apple";
// Elma vs Apple 🍏  No matter the language, they taste the same. 
System.out.println(a.compareToIgnoreCase(b));

What are compareTo & compareToIgnoreCase?

The methods compareTo and compareToIgnoreCase are string comparison mechanisms in Java. compareTo compares strings lexicographically, whereas compareToIgnoreCase does so while ignoring case differences.

When choosing which to use, consider their return values:

Negative: first string is less than the second.
Zero: both strings are equal.
Positive: first string is greater than the second.

Customized sorting with Collator

For sensitive locale-based comparisons, Collator is your go-to. It considers specific language rules and is useful for international applications requiring natural language sorting.

Collator collator = Collator.getInstance(Locale.US);
collator.setStrength(Collator.PRIMARY); // Case and accents don't worry us here
String c = "café";
String d = "cafe";
// Whether your coffee is local or international, we got you covered ☕
System.out.println(collator.compare(c, d));

JDK 8 and JRE 8 supported locales is a handy resource for locale settings.

Why the order matters

In some scenarios, you don't get to ignore the order. Think of:

Sorting user entries for a search function.
Comparing files for a file organization system.
Organizing list items for UI presentations.

Common pitfalls & remedies

Ignoring case: Use toLowerCase() or toUpperCase() before comparing.
Spaces & Punctuation: Use trim() to avoid confusion with invisible characters.
Null pointers: Always check for null before comparing.
Locale usage: Always ensure correct Locale is used with Collator.