String concatenation: concat() vs "+" operator

In Java, you can use the concat() method of the java.lang.String class or the + operator to concatenate (join) two or more strings.

The concat() method returns a new string that is the result of concatenating the specified string to the end of this string. Here is an example of how you can use the concat() method to concatenate two strings:

public class StringConcatenationExample {
  public static void main(String[] args) {
    String str1 = "Hello";
    String str2 = "World";
    String str3 = str1.concat(str2);
    System.out.println(str3);  // Outputs "HelloWorld"
  }
}

The + operator is also used to concatenate strings in Java. When used with two strings, it returns a new string that is the result of concatenating the two strings. Here is an example of how you can use the + operator to concatenate two strings:

public class StringConcatenationExample {
  public static void main(String[] args) {
    String str1 = "Hello";
    String str2 = "World";
    String str3 = str1 + str2;
    System.out.println(str3);  // Outputs "HelloWorld"
  }
}

Both the concat() method and the + operator are used to concatenate strings in Java. The main difference between these two approaches is that the concat() method is a method of the java.lang.String class, while the + operator is a built-in operator in Java.

The + operator is generally considered to be more efficient than the concat() method, because the + operator can be used with other types as well as strings, and the Java compiler can optimize the code to use the StringBuilder class or other techniques to concatenate the strings more efficiently.

For example, when using the + operator to concatenate two strings, the Java compiler may generate code that uses the StringBuilder class to concatenate the strings, like this:

public class StringConcatenationExample {
  public static void main(String[] args) {
    String str1 = "Hello";
    String str2 = "World";
    String str3 = new StringBuilder().append(str1).append(str2).toString();
    System