Concatenate strings in Java
Concatenate string literals (string enclosed in double quotes).
To concatenate strings simply, use + operator.
Since Java8, join method is added to String class, to concatenate strings with delimiter easily.
However, if string is concatenated several times, + operator may affect performance.
(Detailed explanation is not written here)
If string is concatenated several times, we should use StringBuilder.
ConcatenateStringLiteral.java 
public class ConcatenateStringLiteral {
  public static void main(String[] args) {
    // Concatenate string literal simply
    System.out.println("Panda " + "is " + "cute.");

    // Concatenate string literal with delimiter
    // Stinrg.join() is added since java8
    System.out.println(String.join(", ", "Panda", "Giant panda", "Lesser panda"));

    // As needed, please use StringBuilder
    StringBuilder sb = new StringBuilder("Panda");
    sb.append(" is great!");
    System.out.println(sb);
  }
}
Result 
$ javac ConcatenateStringLiteral.java
$ java ConcatenateStringLiteral
Panda is cute.
Panda, Giant panda, Lesser panda
Panda is great!