Concat Strings in Java

Concat Strings in Java | The word concatenation means to add a string to another string. The concatenation can be done by using the “+” operator. Java string class provides concat() method to add a string to another string. In this blog, let us see the different ways to concatenate strings.

How concatenation of String in Java works:-
Example-1:-
String1 = “Hello”
String2 = “world”
After concatenation:- “Hello world”

Example-2:-
String1 = “Hi”
String2 = “Programmer”
After concatenation:- “Hi Programmer”

We can concatenate strings in two ways:-
a) Using the ‘+’ operator
b) By using concat() method of the Java String class

The syntax of the concat() method is as follows:- public String concat(String str)
Parameters:- str the string needed to be combined.
Returns: the string which is combined.

Java String Concat Example

Example-1:- How to concat string in Java using concat()?

public class Main {
   public static void main(String args[]) {
      String string = "Hi, ";
      string = string.concat("Good Morning");
      System.out.println(string);
   }
}

Output:-

Hi, Good Morning

Let us see another example of how to concat strings in Java using concat() method of string class. This time we will apply concat() method multiple times.

Example-2:- How to concat string in Java using concat()?

public class Main {
   public static void main(String args[]) {
      String string1 = "Java";
      String string2 = " Programming";
      String string3 = " Language";

      String string4 = string1.concat(string2);
      System.out.println("string4: " + string4);
      String string5 = string4.concat(string3);
      System.out.println("string5: " + string5);

      String string6 = string1.concat(string2).concat(string3);
      System.out.println("string6: " + string6);
   }
}

Output:-

string4: Java Programming
string5: Java Programming Language
string6: Java Programming Language

Example-3:- How to concat string in Java using concat()?

public class Main {
   public static void main(String args[]) {
      String str1 = "As string";
      System.out.println(str1);
      str1 = str1.concat(" is immutable.");
      System.out.println(str1);
      str1 = str1.concat(" Once created it cannot be changed.");
      System.out.println(str1);
   }
}

Output:-

As string
As string is immutable.
As string is immutable. Once created it cannot be changed.

Example-4:- How to concat string in Java using concat()?

public class Main {
   public static void main(String[] args) {
      String string1 = "Hello, ";
      String string2 = "KnowProgram";
      String string3 = " Reader's.";

      String string4 = string1.concat(string2);
      System.out.println(string4);

      String str5 = string1.concat(string2).concat(string3);
      System.out.println(str5);
   }
}

Output:-

Hello, KnowProgram
Hello, KnowProgram Reader’s.

How to Concat String in Java using + Operator

Not only using the string class concat() method but also using the “+” operator we can concat strings. Let us understand it through an example-1:-

public class Main {
   public static void main(String args[]) {
      String string = "Hi, ";
      string = string + "Good Morning";
      System.out.println(string);
   }
}

Output:-

Hi, Good Morning

Example-2:- How to concat strings in Java using the + operator?

public class Main {
   public static void main(String args[]) {
      String string1 = "Java";
      String string2 = " Programming";
      String string3 = " Language";

      String string4 = string1 + string2;
      System.out.println("string4: " + string4);
      String string5 = string4 + string3;
      System.out.println("string5: " + string5);

      String string6 = string1 + string2 + string3;
      System.out.println("string6: " + string6);
   }
}

Output:-

string4: Java Programming
string5: Java Programming Language
string6: Java Programming Language

Example-3:- How to concat strings in Java using the + operator?

public class Main {
   public static void main(String args[]) {
      String str1 = "As string";
      System.out.println(str1);
      str1 = str1 + " is immutable.";
      System.out.println(str1);
      str1 = str1 + " Once created it cannot be changed.";
      System.out.println(str1);
   }
}

Output:-

As string
As string is immutable.
As string is immutable. Once created it cannot be changed.

Example-4:- How to concat strings in Java using the + operator?

public class Main {
   public static void main(String[] args) {
      String string1 = "Hello, ";
      String string2 = "KnowProgram";
      String string3 = " Reader's.";

      String string4 = string1 + string2;
      System.out.println(string4);

      String str5 = string1 + string2 + string3;
      System.out.println(str5);
   }
}

Output:-

Hello, KnowProgram
Hello, KnowProgram Reader’s.

Java Concat Array Of Strings

We have seen how to concat strings in Java using concat() method or using the concatenation operator (+). Now let us develop a simple for its use case. We have an array of strings and we have to concat it to make a single string.

import java.util.Arrays;

public class Main {
   public static void main(String[] args) {
      String lang[] = 
         { "Java ", "Python ", "HTML ", "C++ ", "CSS" };
      String string = "";

      for (String str : lang) {
         string = string.concat(str);
      }
      System.out.println("String array: " 
                  + Arrays.toString(lang));

      System.out.println("String Array Merging: " + string);
   }
}

Output:-

String array: [Java , Python , HTML , C++ , CSS]
String Array Merging: Java Python HTML C++ CSS

We can also use the “+” operator to concat array of strings. For this, in for loop we have to use the concatenation operator “+” instead of the Java string concat() method. And we will get the same result.

for (String str : lang) {
   string += str;
}

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