The overloaded + and += operators perform functions similar to the concat() method : String class « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. String class

public class MainClass {
  public static void main(String[] argv) {
    String x = "library";
    System.out.println(x + " card"); // output is "library card"

    x = "A";
    x += " ocean";
    System.out.println(x); // output is "A ocean"

  }
}

library card
A ocean