Java String concat

The Java String class concat() method combines specified string at the end of this string. It returns a combined string. It is like appending another string.

Signature

The signature of the string concat() method is given below:

Parameter

anotherString : another string i.e., to be combined at the end of this string.

Returns

combined string

Internal implementation

public String concat(String str) {  
       int otherLen = str.length();  
       if (otherLen == 0) {  
           return this;  
       }  
       int len = value.length;  
       char buf[] = Arrays.copyOf(value, len + otherLen);  
       str.getChars(buf, len);  
       return new String(buf, true);  
   }  

Java String concat() method example

FileName: ConcatExample.java

public class ConcatExample{  
public static void main(String args[]){  
String s1="java string";  
// The string s1 does not get changed, even though it is invoking the method    
// concat(), as it is immutable. Therefore, the explicit assignment is required here.
s1.concat("is immutable");  
System.out.println(s1);  
s1=s1.concat(" is immutable so assign it explicitly");  
System.out.println(s1);  
}}  

Test it Now

Output:

java string
java string is immutable so assign it explicitly

Java String concat() Method Example 2

Let's see an example where we are concatenating multiple string objects.

FileName: ConcatExample2.java

public class ConcatExample2 {
	public static void main(String[] args) {	
		String str1 = "Hello";
		String str2 = "Javatpoint";
		String str3 = "Reader";
		// Concatenating one string 
		String str4 = str1.concat(str2);		
		System.out.println(str4);
		// Concatenating multiple strings
		String str5 = str1.concat(str2).concat(str3);
		System.out.println(str5);
	}
}

Output:

HelloJavatpoint
HelloJavatpointReader

Java String concat() Method Example 3

Let's see an example where we are concatenating spaces and special chars to the string object. It is done using the chaining of the concat() method.

FileName: ConcatExample3.java

public class ConcatExample3 {
	public static void main(String[] args) {
		String str1 = "Hello";
		String str2 = "Javatpoint";
		String str3 = "Reader";
		// Concatenating Space among strings
		String str4 = str1.concat(" ").concat(str2).concat(" ").concat(str3);
		System.out.println(str4);		
		// Concatenating Special Chars		
		String str5 = str1.concat("!!!");
		System.out.println(str5);		
		String str6 = str1.concat("@").concat(str2);
		System.out.println(str6);
	}
}

Output:

Hello Javatpoint Reader
Hello!!!
<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="afe7cac3c3c0efe5ced9cedbdfc0c6c1db">[email�protected]</a>

Java String concat() Method Example 4

Till now, we have seen that the concat() method appends the string at the end of the string that invokes the method. However, we can do a bit of workaround to append the string at the beginning of a string using the concat() method.

FileName: ConcatExample4.java

// A Java program that shows how to add 
// a string at the beginning of another string
public class ConcatExample4
{
// main method
public static void main(String argvs[])
{
String str = "Country";

// we have added the string "India is my" before the String str;
// Also, observe that a string literal can also invoke the concat() method
String s = "India is my ".concat(str);

// displaying the string
System.out.println(s);

}
}

Output: