Arrays and Strings - Beginning Java 2 SDK - page 132

We select a random element from the array by creating a random index value within the output
statement with the expression (int)(stars.length*Math.random()) . Multiplying the random
number produced using the method Math.random() by the length of the array, we will get a value
between 0.0 and 6.0 since the value returned by random() will be between 0.0 and 1.0. The result
won't ever be 6.0 because the value returned by the random() method is strictly less than 1.0, which is
just as well as this would be an illegal index value. The result is then cast to an int , making it a valid
array index value.
Thus the program selects a random string from the array and displays it.
Operations on Strings
There are many kinds of operations that can be performed on strings, but we can start with one you
have used already, joining strings together, often called string concatenation .
Joining Strings
To join two String objects to form a 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 will join the two strings on the right of the assignment, and store the result in the String variable
myString . The + operation generates a completely new String object that is separate from the
original String objects that are the operands, and this new object is stored in myString .
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 will refer to the string " Too many cooks spoil
the broth ". Note that 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
on the following page.