Java Cookbook, 4th Edition by Ian F. Darwin

Author:Ian F. Darwin [Ian F. Darwin]
Language: eng
Format: epub
Publisher: O'Reilly Media, Inc.
Published: 2020-04-24T16:00:00+00:00

Figure 3-1. String, StringBuilder, and C-language strings

Although we haven’t discussed the details of the java.io package yet (we will, in [Link to Come]), you need to be able to read text files for some of these programs. Even if you’re not familiar with java.io, you can probably see from the examples of reading text files that a BufferedReader allows you to read “chunks” of data, and that this class has a very convenient readLine() method.

Going the other way, System.out.println() is normally used to print strings or other values to the terminal or “standard output.” String concatenation is commonly used here, as in:

System.out.println("The answer is " + result);

One caveat with string concatenation is that if you are appending a bunch of things, and a number and a character are concatenated at the front, they are added before concatenation due to Java’s precedence rules. So don’t do as I did in this contrived example:

int result = ...; System.out.println(result + '=' + " the answer.");

Given that result is an integer, then result + '=' (result added to the equals sign, which is of the numeric type char) is a valid numeric expression, which will result in a single value of type int. If the variable result has the value 42, and given that the character = in a Unicode (or ASCII) code chart has the value 61, this prints:

103 the answer.

The wrong value and no equals sign! Safer approaches include using parentheses, using double quotes around the equals sign, using a StringBuilder (see Recipe 3.2) or a MessageFormat (see [Link to Come]), or using String.format() (see [Link to Come]). Of course in this simple example you could just move the = to be part of the string literal, but the example was chosen to illustrate the problem of arithmetic on char values being confused with string contatenation. I won’t show you how to sort an array of strings here; the more general notion of sorting a collection of objects will be taken up in [Link to Come].

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