How to Compare two Strings in Java?

In this article, you will learn How to Compare two Strings in Java? String is a succession of characters. In Java, objects of String are permanent which implies they are steady and can’t be changed once made. The following are 5 methods for contrasting two Strings in Java: Attention peruser! Try not to quit adapting now. Get hold of all the significant Java Foundation and Collections ideas with the Fundamentals of Java and Java Collections Course at an understudy cordial cost and become industry prepared. To finish your readiness from learning a language to DS Algo and some more.

Utilizing client characterized work: Define a capacity to contrast esteems and following conditions :

if (string1 > string2) it returns a positive worth.
if both the strings are equivalent lexicographically
i.e.(string1 == string2) it brings 0 back.
if (string1 < string2) it returns a negative worth.
The worth is determined 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();
        int lmin = Math.min(l1, l2);
 
        for (int i = 0; i < lmin; i++) {
            int str1_ch = (int)str1.charAt(i);
            int str2_ch = (int)str2.charAt(i);
 
            if (str1_ch != str2_ch) {
                return str1_ch - str2_ch;
            }
        }
 
        // Edge case for strings like
        // String 1="Geeks" and String 2="Geeksforgeeks"
        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 any character does 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 the contents of both the Strings are same 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: true

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 use == for comparison of Strings?

In general both equals() and “==” operators 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 two String objects are being created namely s1 and s2.

- Both s1 and s2 refer 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 compares the values given in s1 and s2

Also Read: How to implement recursion in C++?

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