Compare two Strings in Java

String is a sequence of characters. In java, objects of String are immutable which means they are constant and cannot be changed once created.

Below are 5 ways to compare two Strings in Java:

Using user-defined function : Define a function to compare values with following conditions :

if (string1 > string2) it returns a positive value.
if both the strings are equal lexicographically
i.e.(string1 == string2) it returns 0.
if (string1 < string2) it returns a negative value.

The value is calculated as (int)str1.charAt(i) – (int)str2.charAt(i)

Examples:

Input 1: GeeksforGeeks
Input 2: Practice
Output: -9

Input 1: Geeks
Input 2: Geeks
Output: 0

Input 1: GeeksforGeeks
Input 2: Geeks
Output: 8

Program:

// Java program to Compare two strings 
// lexicographically 
public class GFG { 
  
    // This method compares two strings 
    // lexicographically without using 
    // library functions 
    public static int stringCompare(String str1, String str2) 
    { 
  
        int l1 = str1.length(); 
        int l2 = str2.length(); 
  
        for (int i = 0; i < l1 && i < l2; i++) { 
            int str1_ch = (int)str1.charAt(i); 
            int str2_ch = (int)str2.charAt(i); 
  
            if (str1_ch == str2_ch) { 
                continue; 
            } 
            else { 
                return str1_ch - str2_ch; 
            } 
        } 
  
        // Edge case for strings like 
        // String 1="Geeks" and String 2="Geeksforgeeks" 
        if (l1 < l2) { 
            return l1 - l2; 
        } 
        else if (l1 > l2) { 
            return l1 - l2; 
        } 
  
        // If none of the above conditions is true, 
        // it implies both the strings are equal 
        else { 
            return 0; 
        } 
    } 
  
    // Driver function to test the above program 
    public static void main(String args[]) 
    { 
        String string1 = new String("Geeksforgeeks"); 
        String string2 = new String("Practice"); 
        String string3 = new String("Geeks"); 
        String string4 = new String("Geeks"); 
  
        // Comparing for String 1 < String 2 
        System.out.println("Comparing " + string1 + " and " + string2 
                           + " : " + stringCompare(string1, string2)); 
  
        // Comparing for String 3 = String 4 
        System.out.println("Comparing " + string3 + " and " + string4 
                           + " : " + stringCompare(string3, string4)); 
  
        // Comparing for String 1 > String 4 
        System.out.println("Comparing " + string1 + " and " + string4 
                           + " : " + stringCompare(string1, string4)); 
    } 
} 

Output:

Comparing Geeksforgeeks and Practice : -9
Comparing Geeks and Geeks : 0
Comparing Geeksforgeeks and Geeks : 8

Using String.equals() :In Java, string equals() method compares the two given strings based on the data/content of the string. If all the contents of both the strings are same then it returns true. If all characters do not match, then it returns false.

Syntax:

str1.equals(str2);

Here str1 and str2 both are the strings which are to be compared.

Examples:

Input 1: GeeksforGeeks
Input 2: Practice
Output: false

Input 1: Geeks
Input 2: Geeks
Output: true

Input 1: geeks
Input 2: Geeks
Output: false

Program:

// Java program to Compare two strings 
// lexicographically 
public class GFG { 
    public static void main(String args[]) 
    { 
        String string1 = new String("Geeksforgeeks"); 
        String string2 = new String("Practice"); 
        String string3 = new String("Geeks"); 
        String string4 = new String("Geeks"); 
        String string5 = new String("geeks"); 
  
        // Comparing for String 1 != String 2 
        System.out.println("Comparing " + string1 + " and " + string2 
                           + " : " + string1.equals(string2)); 
  
        // Comparing for String 3 = String 4 
        System.out.println("Comparing " + string3 + " and " + string4 
                           + " : " + string3.equals(string4)); 
  
        // Comparing for String 4 != String 5 
        System.out.println("Comparing " + string4 + " and " + string5 
                           + " : " + string4.equals(string5)); 
  
        // Comparing for String 1 != String 4 
        System.out.println("Comparing " + string1 + " and " + string4 
                           + " : " + string1.equals(string4)); 
    } 
} 

Output:

Comparing Geeksforgeeks and Practice : false
Comparing Geeks and Geeks : true
Comparing Geeks and geeks : false
Comparing Geeksforgeeks and Geeks : false

Using String.equalsIgnoreCase() : The String.equalsIgnoreCase() method compares two strings irrespective of the case (lower or upper) of the string. This method returns true if the argument is not null and it returns an equivalent String ignoring case, else false.

Syntax:

str2.equalsIgnoreCase(str1);

Here str1 and str2 both are the strings which are to be compared.

Examples:

Input 1: GeeksforGeeks
Input 2: Practice
Output: false

Input 1: Geeks
Input 2: Geeks
Output: true

Input 1: geeks
Input 2: Geeks
Output: false

Program:

// Java program to Compare two strings 
// lexicographically 
public class GFG { 
    public static void main(String args[]) 
    { 
        String string1 = new String("Geeksforgeeks"); 
        String string2 = new String("Practice"); 
        String string3 = new String("Geeks"); 
        String string4 = new String("Geeks"); 
        String string5 = new String("geeks"); 
  
        // Comparing for String 1 != String 2 
        System.out.println("Comparing " + string1 + " and " + string2 
                           + " : " + string1.equalsIgnoreCase(string2)); 
  
        // Comparing for String 3 = String 4 
        System.out.println("Comparing " + string3 + " and " + string4 
                           + " : " + string3.equalsIgnoreCase(string4)); 
  
        // Comparing for String 4 = String 5 
        System.out.println("Comparing " + string4 + " and " + string5 
                           + " : " + string4.equalsIgnoreCase(string5)); 
  
        // Comparing for String 1 != String 4 
        System.out.println("Comparing " + string1 + " and " + string4 
                           + " : " + string1.equalsIgnoreCase(string4)); 
    } 
} 

Output:

Comparing Geeksforgeeks and Practice : false
Comparing Geeks and Geeks : true
Comparing Geeks and geeks : true
Comparing Geeksforgeeks and Geeks : false

Using Objects.equals() : Object.equals(Object a,Object b) method returns true if the arguments are equal to each other and false otherwise. Consequently, if both arguments are null, true is returned and if exactly one argument is null, false is returned. Otherwise, equality is determined by using the equals() method of the first argument.

Syntax:

public static boolean equals(Object a, Object b)

Here a and b both are the string objects which are to be compared.

Examples:

Input 1: GeeksforGeeks
Input 2: Practice
Output: false

Input 1: Geeks
Input 2: Geeks
Output: true

Input 1: null
Input 2: null
Output: true

Program:

// Java program to Compare two strings 
// lexicographically 
  
import java.util.*; 
  
public class GFG { 
    public static void main(String args[]) 
    { 
        String string1 = new String("Geeksforgeeks"); 
        String string2 = new String("Geeks"); 
        String string3 = new String("Geeks"); 
        String string4 = null; 
        String string5 = null; 
  
        // Comparing for String 1 != String 2 
        System.out.println("Comparing " + string1 + " and " + string2 
                           + " : " + Objects.equals(string1, string2)); 
  
        // Comparing for String 2 = String 3 
        System.out.println("Comparing " + string2 + " and " + string3 
                           + " : " + Objects.equals(string2, string3)); 
  
        // Comparing for String 1 != String 4 
        System.out.println("Comparing " + string1 + " and " + string4 
                           + " : " + Objects.equals(string1, string4)); 
  
        // Comparing for String 4 = String 5 
        System.out.println("Comparing " + string4 + " and " + string5 
                           + " : " + Objects.equals(string4, string5)); 
    } 
} 

Output:

Comparing Geeksforgeeks and Geeks : false
Comparing Geeks and Geeks : true
Comparing Geeksforgeeks and null : false
Comparing null and null : true

Using String.compareTo() :

Syntax:

int str1.compareTo(String str2)

Working:
It compares and returns the following values as follows:

if (string1 > string2) it returns a positive value.
if both the strings are equal lexicographically
i.e.(string1 == string2) it returns 0.
if (string1 < string2) it returns a negative value.

Examples:

Input 1: GeeksforGeeks
Input 2: Practice
Output: -9

Input 1: Geeks
Input 2: Geeks
Output: 0

Input 1: GeeksforGeeks
Input 2: Geeks
Output: 8

Program:

// Java program to Compare two strings 
// lexicographically 
  
import java.util.*; 
  
public class GFG { 
    public static void main(String args[]) 
    { 
        String string1 = new String("Geeksforgeeks"); 
        String string2 = new String("Practice"); 
        String string3 = new String("Geeks"); 
        String string4 = new String("Geeks"); 
  
        // Comparing for String 1 < String 2 
        System.out.println("Comparing " + string1 + " and " + string2 
                           + " : " + string1.compareTo(string2)); 
  
        // Comparing for String 3 = String 4 
        System.out.println("Comparing " + string3 + " and " + string4 
                           + " : " + string3.compareTo(string4)); 
  
        // Comparing for String 1 > String 4 
        System.out.println("Comparing " + string1 + " and " + string4 
                           + " : " + string1.compareTo(string4)); 
    } 
} 

Output:

Comparing Geeksforgeeks and Practice : -9
Comparing Geeks and Geeks : 0
Comparing Geeksforgeeks and Geeks : 8

Why not to use == for comparison of Strings?

In general both equals() and “==” operator in Java are used to compare objects to check equality but here are some of the differences between the two:

Main difference between .equals() method and == operator is that one is method and other is operator.
One can use == operators for reference comparison (address comparison) and .equals() method for content comparison.

In simple words, == checks if both objects point to the same memory location whereas .equals() evaluates to the comparison of values in the objects.

Example:

// Java program to understand   
// why to avoid == operator  
  
public class Test {  
    public static void main(String[] args)  
    {  
        String s1 = new String("HELLO");  
        String s2 = new String("HELLO");  
  
        System.out.println(s1 == s2);  
  
        System.out.println(s1.equals(s2));  
    }  
}  

Output:

false
true

Explanation: Here String objects are being created namely s1 and s2.

Both s1 and s2 refers to different objects.
When one uses == operator for s1 and s2 comparison then the result is false as both have different addresses in memory.
Using equals, the result is true because its only comparing the values given in s1 and s2.

My Personal Notes

Nov	DEC	Jan
	19
2017	2018	2019

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