6 ways to Concatenate Strings in Java (Bonus: Choose concatenation character)

We need to deal with Strings in real time projects, and concatenation of Strings is a common and important functionality. There are multiple ways supported in Java to concatenate 2 or more Strings.

Let's try to understand what are our options:

1. Using the '+' operator

This is the easiest and the most commonly used option. We can simply use '+' between 2 Strings to concatenate them.

String s1 = "Hello";
String s2 = "World";
		
System.out.println(s1+s2);

Output:

HelloWorld

2. Using concat() function

Java has inbuilt function for concatenation. + operator is used for addition operations as well. If you want your code to be specific and readable, concat() function is an easy approach.

String s1 = "Hello";
String s2 = "World";
		
System.out.println(s1.concat(s2));

Output:

HelloWorld

3. Using StringBuilder class

StringBuilder class has inbuilt methond append(), which we can use for concatenation operation.

StringBuilder sb1 = new StringBuilder("String");
StringBuilder sb2 = new StringBuilder("Builder");
		
System.out.println(sb1.append(sb2));

Output:

StringBuilder

4. Using String format() method

String format is a functionality, which we can utilize to concatenate Strings. 

String s1 = "Hello";
String s2 = "World";

System.out.println(String.format("%s%s", s1,s2));

Output:

HelloWorld

5. Using String join() method

String.join() function is another method which can be utilized for concatenation. Bonus part is, you can specify the concatenation character. So, if you want a space character between all your Strings, this method gives you that flexibility.

String s1 = "Hello";
String s2 = "World";

System.out.println(String.join(" ", s1,s2));

Output:

Hello World

6. Using StringJoiner class

We can utilize StringJoiner class to concatenate Strings. As with String.join() method, this class also adds a bonus functionality of choosing a concatenation operator. 

import java.util.StringJoiner;

String s1 = "Hello";
String s2 = "World";

StringJoiner sj1 = new StringJoiner(",");
sj1.add(s1);
sj1.add(s2);
		
System.out.println(sj1.toString());

Output:

Hello,World

Just to reiterate all the options we have, let's have a single piece of code for your reference, which includes all the above options:

import java.util.StringJoiner;

public class ConcatString {

	public static void main(String[] args) {

		String s1 = "Hello";
		String s2 = "World";
		
		//Option 1
		System.out.println(s1+s2);
		
		//Option 2
		System.out.println(s1.concat(s2));
		
		StringBuilder sb1 = new StringBuilder("String");
		StringBuilder sb2 = new StringBuilder("Builder");
		
		//Option 3
		System.out.println(sb1.append(sb2));
		
		//Option 4
		System.out.println(String.format("%s%s", s1,s2));
		
		//Option5
		System.out.println(String.join(" ", s1,s2));
		
		StringJoiner sj1 = new StringJoiner(",");
		sj1.add(s1);
		sj1.add(s2);
		
		//Option 6
		System.out.println(sj1.toString());
		
	}

}

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