Using Other Variables with Strings

Although you can use the + operator to paste two strings together, as demonstrated in the preceding section, you will use it more often to link strings and variables. Take a look at the following:

int length = 121;

char rating = 'R';

System.out.println("Running time: " + length + " minutes");

System.out.println("Rated " + rating);

This code will be displayed as the following:

Running time: 121 minutes

Rated R

This example displays a unique facet about how the + operator works with strings. It can cause variables that are not strings to be treated just like strings when they are displayed. The variable length is an integer set to the value 121. It is displayed between the strings Running time: and minutes. The System.out.println() statement is being asked to display a string plus an integer, plus another string. This statement works because at least one part of the group is a string. The Java language offers this functionality to make displaying information easier.

One thing you might want to do with a string is paste something to it several times, as in the following example:

String searchKeywords = "";

searchKeywords = searchKeywords + "drama ";

searchKeywords = searchKeywords + "romance ";

searchKeywords = searchKeywords + "New Zealand";

This code would result in the searchKeywords variable being set to "drama ro-mance New Zealand." The first line creates the searchKeywords variable and sets it to be an empty string, because there's nothing between the double quotation marks.

The second line sets the searchKeywords variable equal to its current string, plus the string drama added to the end. The next two lines add "romance" and "New Zealand" in the same way.

As you can see, when you are pasting more text at the end of a variable, the name of the variable has to be listed twice. Java offers a shortcut to simplify this process a bit: the += operator. The += operator combines the functions of the = and + operators. With strings, it is used to add something to the end of an existing string. The searchKeywords example can be shortened by using +=, as shown in the following code:

String searchKeywords = "";

searchKeywords += "drama ";

searchKeywords += "romance ";

searchKeywords += "New Zealand";

This code produces the same result: searchKeywords is set to "drama romance New Zealand."