Difference between concat() and + operator in Java

concat() Method

The Java String concat() method concatenates one string to the end of another string. This method returns a string with the value of the string passed into the method, appended to the end of the string.

Example:

Output:

Gfg! is the best.

+ operator

+ operator is used to concatenate strings on either side.

Example:

Output:

Gfg! is the best.

Although concat() and + operator are both used for concatenation of strings, but there are some differences between them:

1. Number of arguments the concat() method and + operator takes:
   • concat() method takes only one argument of string and concat it with other string.
   • + operator takes any number of arguments and concatenates all the strings.
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   public class GFG {     public static void main(String[] args)     {         String s = "Geeks", t = "for", g = "geeks";            System.out.println(s + t + g);         System.out.println(s.concat(t));     } }

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   Output:

   Geeksforgeeks
   Geeksfor
   

2. Type of arguments :
   • strong>concat() method takes only string arguments, if there is any other type is given in arguments then it will raise an error.
   • + operator takes any type and converts to string type and then concatenates the strings.
3. concat() method raises java.lang.NullPointer Exception
   • concat() method throws NullPointer Exception when string is concatenated with null
   • + operator did not raise any Exception when the string is concatenated with null.
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   public class GFG {     public static void main(String[] args)     {         String s = "Geeks";         String r = null;         System.out.println(s + r);            // It raises an NullPointer Exception         System.out.println(s.concat(r));     } }

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   Output:

   
   Geeksnull
   Exception in thread "main" java.lang.NullPointerException
       at java.lang.String.concat(String.java:2027)
       at GFG.main(GFG.java:7)
   

4. Creates a new String object.
   • concat() method takes concatenates two strings and return new string object only string length is greater than 0, otherwise it returns same object.
   • + operator creates a new string object every time irrespective of length of string.
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   public class GFG {     public static void main(String[] args)     {            String s = "Geeks", g = "";         String f = s.concat(g);         if (f == s)             System.out.println("Both are same");         else             System.out.println("not same");         String e = s + g;         if (e == s)             System.out.println("Both are same");         else             System.out.println("not same");     } }

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   Output:

   Both are same
   not same
   

5. Performance:
   concat() method is better than + operator because it creates a new object only when the string length is greater than zero(0) but + operator always a creates a new string irrespective of length of string.

Difference table:

bestharadhakrishna

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