Java String compareTo() method - Syntax and Examples

Introduction

The compareTo() method in Java is a powerful tool for comparing strings. It doesn't just tell you if two strings are the same or different; it tells you *how* they differ based on their lexicographical order (essentially, dictionary order). Think of it like how words are arranged alphabetically - that's what compareTo() does for your strings.

Syntax

public int compareTo(String anotherString)

Parameters

Parameter	Description
anotherString	The string to compare with the current string.

Return Value

The compareTo() method returns an integer value, which indicates the relationship between the two strings:

• If the current string is lexicographically less than anotherString, it returns a negative integer.
• If the current string is lexicographically greater than anotherString, it returns a positive integer.
• If the two strings are equal, it returns 0.

Examples

Example 1: Basic Comparison

This example demonstrates a simple comparison between two strings.

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

int result = str1.compareTo(str2);
System.out.println(result); // Output: -1

-1

Explanation: Since "apple" comes before "banana" alphabetically, str1.compareTo(str2) returns a negative value (-1).

Example 2: Strings are Equal

This example shows what happens when the strings being compared are identical.

String str1 = "orange";
String str2 = "orange";

int result = str1.compareTo(str2);
System.out.println(result); // Output: 0

0

Explanation: Because both strings are exactly the same, compareTo() returns 0.

Example 3: Strings in Reverse Order

This example illustrates a comparison where the first string comes after the second alphabetically.

String str1 = "zebra";
String str2 = "apple";

int result = str1.compareTo(str2);
System.out.println(result); // Output: 1

1

Explanation: "zebra" comes after "apple", so the result is a positive integer (1).

Example 4: Case Sensitivity

This example highlights that compareTo() is case-sensitive.

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

int result = str1.compareTo(str2);
System.out.println(result); // Output: 1

1

Explanation: Because "Apple" (uppercase 'A') has a higher Unicode value than "apple" (lowercase 'a'), compareTo() considers "Apple" greater and returns a positive value.

Example 5: Comparing Strings with Numbers

This example demonstrates comparing strings that contain numbers. The comparison is based on the string representation, not numerical values.

String str1 = "file10";
String str2 = "file2";

int result = str1.compareTo(str2);
System.out.println(result); // Output: 1

1

Explanation: The comparison is done lexicographically, treating the strings as text. "file10" comes after "file2" because '1' comes after '2' when compared as characters.