Java String comparison, differences between ==, equals, matches, compareTo().

When working with strings in Java, one of the most common operations is comparing strings to check for equality or ordering. Java provides several methods to perform string comparison: equals(), matches(), and compareTo(). While all of them are used to compare strings, each method serves a different purpose and behaves differently.  

Different approaches

Following are the different approaches for string comparison ?

• equals() Method
• matches() Method
• compareTo() Method

When to Use Each Method

• Use equals() when you need to check if two strings are identical in content.
  
• Use matches() when you need to check if a string follows a specific pattern, such as validating formats like email addresses, phone numbers, or any other custom regular expressions.
  
• Use compareTo() when you need to order or sort strings based on their lexicographical order.

equals() Method

The equals() method compares this string to the specified object. The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object. 

Syntax

public boolean equals(Object obj)

Key Points

• It performs a case-sensitive comparison of the string's content.
  
• It returns true if the strings are exactly the same (case-sensitive).
  
• It is not null-safe; calling equals() on a null reference will result in a NullPointerException.

Example

public class Sample{
   public static void main(String []args){
      String s1 = "tutorialspoint";
      String s2 = "tutorialspoint";
      String s3 = new String ("Tutorials Point");
      System.out.println(s1.equals(s2));
      System.out.println(s2.equals(s3));
   }
}

Output

true
false

You can also compare two strings using the == operator. But, it compares references of the given variables not values.

matches() Method

The matches() method of the String class tells whether or not this string matches the given regular expression. An invocation of this method of the form str.matches(regex) yields exactly the same result as the expression Pattern.matches(regex, str).

Syntax

public boolean matches(String regex)

Key Points

• It is specifically used for pattern matching.
  
• The string is checked against the entire regular expression.
  
• Unlike equals(), it can perform more complex comparisons such as matching specific patterns (e.g., email addresses, phone numbers, etc.).

Example

public class Sample {
   public static void main(String []args) {
      String s1 = "tutorialspoint";
      String s2 = "tutorialspoint";
      String s3 = new String ("Tutorials Point");
      System.out.println(s1 == s2);
      System.out.println(s2 == s3);
   }
}

Output

true
false

compareTo() Method

The compareTo() method is used to compare two strings lexicographically. This method returns an integer value:

• 0 if the strings are equal,
• A negative integer if the first string is lexicographically less than the second string,
  
• A positive integer if the first string is lexicographically greater than the second string.

Syntax

public int compareTo(String anotherString)

Key Points

• It compares the strings based on their Unicode values.
  
• It is case-sensitive.
  
• It is useful when you need to order strings (e.g., sorting).

Example 

import java.io.*;
public class Test {
   public static void main(String args[]) {
      String Str = new String("Welcome to Tutorialspoint.com");
      System.out.print("Return Value :" );
      System.out.println(Str.matches("(.*)Tutorials(.*)"));
      System.out.print("Return Value :" );
      System.out.println(Str.matches("Tutorials"));
      System.out.print("Return Value :" );
      System.out.println(Str.matches("Welcome(.*)"));
   }
}

Output

Return Value :true
Return Value :false
Return Value :true

Key Differences Between equals(), matches(), and compareTo()

Below is the comparison table to show the key differences between equals(), matches(), and compareTo() ?

Method	Purpose	Comparison Type	Case Sensitivity	Use Case
equals()	Check if two strings are the same	Exact equality	Case-sensitive	Comparing two strings for equality.
matches()	Checks if the string matches a regular expression	Pattern matching (regex)	Case-sensitive	Validating strings against patterns (e.g., email)
compareTo()	Compares two strings lexicographically	Lexicographical order	Case-sensitive	Ordering strings or sorting.