Table of Contents

Java concat() method

The Java concat() method is used to combine two strings into one. It’s a method of the String class. This method appends one string to the end of another. The method returns a String with the value of the String passed into the method, appended to the end of the String, used to invoke this method.

Method signature

public String concat(String str)

str: The string to be concatenated to the end of the current string.

The concat() method returns a new string that is the concatenation of the current string and the string provided as a parameter. The original string is not modified because strings in Java are immutable.

Example

Let’s understand the usage of the method with an example program:

package com.testingdocs.stringmethods;

public class ExampleProgram {

 public static void main(String[] args) {
 String str = "TestingDocs";
 System.out.println(str.hashCode());
 // concat() method demo
 str = str.concat(".com");
 System.out.println(str);
 System.out.println(str.hashCode());
 }
}

Program Output

The output of the program is as follows:

1555687499
TestingDocs.com
566048094

Notice that the hashCode of the string variable is different before and after the concatenation. This is because, in Java, String objects are immutable, meaning once a String object is created, it cannot be modified. When you perform a concatenation operation, a new String object is created.

When you concatenate strings, a new String object is created. The hashCode of a String is computed based on its content.