concat(..) method is used to concatenate two Strings.
Say, we want to join String "Hello" and "World" and make it "HelloWorld".
public class Test{
public static void main(String[] arg){
String firstString = "Hello";
String secondString = "World";
String finalString = firstString.concat(secondString);
System.out.println("The combined String is : "+finalString);
}
}