Arrays and Strings - Beginning Java - page 158

There are many kinds of operations that can be performed on strings, but let's start with one you have used
already, joining two or more strings to form a new, combined string. This is often called string concatena-
tion .
Joining Strings
To join two String objects to form a new, single string you use the + operator, just as you have been doing
with the argument to the println() method in the program examples thus far. The simplest use of this is to
join two strings together:
myString = "The quick brown fox" + " jumps over the lazy dog";
This joins the two strings on the right of the assignment and stores the result in the String variable
myString . The + operation generates a completely new String object that is separate from the two original
String objects that are the operands, and a reference to this new object is stored in myString . Of course,
you also use the + operator for arithmetic addition, but if either of the operands for the + operator is a String
object or literal, then the compiler interprets the operation as string concatenation and converts the operand
that is not a String object to a string.
Here's an example of concatenating strings referenced by String variables:
String date = "31st ";
String month = "December";
String lastDay = date + month; // Result is "31st December"
If a String variable that you use as one of the operands to + contains null , then this is automatically
converted to the string "null" . So if the month variable were to contain null instead of a reference to the
string “ December ”, the result of the concatenation with date would be the string "31st null" .
Note that you can also use the += operator to concatenate strings. For example:
String phrase = "Too many";
phrase += " cooks spoil the broth";
After executing these statements, the variable phrase refers to the string "Too many cooks spoil the
broth" . Of course, this does not modify the string "Too many" . The string that is referenced by phrase
after this statement has been executed is a completely new String object. This is illustrated in Figure 4-7 .
FIGURE 4-7