Java String Comparison: A Comprehensive Guide

The String class includes several methods that compare strings or substrings within strings. Each is examined here.

There are three ways to compare string in java:

1. By equals() method
2. By = = operator
3. By compareTo() method

1) String compare by equals() method

The String equals() method compares the original content of the string. It compares values of string for equality. String class provides two methods:

Program: equals

class Stringcomparison{

 public static void main(String args[]){
   String s1="Rahim";
   String s2="Rahim";
   String s3=new String("Rahim");
   String s4="Ram";
   System.out.println(s1.equals(s2));//true
   System.out.println(s1.equals(s3));//true
   System.out.println(s1.equals(s4));//false
 }
}

Output

true
true
false
Press any key to continue . . .

Program: equalsIgnoreCase

class Teststringcomparison{
 public static void main(String args[]){
   String s1="RAMBO";
   String s2="rambo";

   System.out.println(s1.equals(s2));//false
   System.out.println(s1.equalsIgnoreCase(s2));//true
 }
}

Output

false
true
Press any key to continue . . .

More examples Program

Program

public class StringCompare{
   public static void main(String args[]){
      String str = "Hello Rambo";
      String anotherString = "hello rambo";
      Object objStr = str;

      System.out.println( str.compareTo(anotherString) );
      System.out.println( str.compareToIgnoreCase(anotherString) );
      System.out.println( str.compareTo(objStr.toString()));
   }
}

Output

The above code sample will produce the following result.

-32
0
0
Press any key to continue . . .

2) String compare by == operator

This operators that can be used with object references are comparing for equality (==). These operators compare two values to see if they refer to the same object. Although this comparison is very fast,

Program

class Stringcomparison {
 public static void main(String args[]){
   String s1="Atnyla";
   String s2="Atnyla";
   String s3=new String("Atnyla");
   System.out.println(s1==s2);//true (because both refer to same instance)
   System.out.println(s1==s3);//false(because s3 refers to instance created in nonpool)
 }
}

Output

The above code sample will produce the following result.

true
false
Press any key to continue . . .

3) String compare by compareTo() method

The String compareTo() method compares values lexicographically and returns an integer value that describes if first string is less than, equal to or greater than second string.

Suppose s1 and s2 are two string variables. If:

• stng1 == stng2 :0
• stng1 > stng2   :positive value
• stngs1 < stng2   :negative value

Program

class Stringcomparison {
 public static void main(String args[]){
   String stng1="Atnyla";
   String stng2="Atnyla";
   String stng3="Rambo";
   System.out.println(stng1.compareTo(stng2));//0
   System.out.println(stng1.compareTo(stng3));//1(because stng1>s3)
   System.out.println(stng3.compareTo(stng1));//-1(because stng3 < s1 )
 }
}

Output

0
-17
17
Press any key to continue . . .

Equality comparison: One way for primitives, Four ways for objects