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that delimit the throws clause Throws IOException in the header of the method.
This signals that this method may throw an IOException . Now, this method is
syntactically correct, but the method that called this one may be syntactically
incorrect and will also need a throws clause, and so on.
The upshot of this is that if the statement br.readLine() causes an
IOException , the system will print an error message and terminate execution of
the program.
For a complete discussion of handling exceptions, see Chap. 10.
Extracting numbers
Assume that a line "-77" of keyboard input has been placed in String vari-
able line and that our task is to extract the integer from line and place it in int
variable i . Static function parseInt of wrapper class Integer will do the job:
execution of:
i= Integer.parseInt(line);
converts the string in variable line to an integer and stores the integer in vari-
able i .
The two statements to read in a line of keyboard input and extract the inte-
ger in it can be combined to avoid declaring the unnecessary variable line :
i= Integer.parseInt(br.readLine());
But there is a problem with function parseInt : it does not allow white-
space, like blank characters, to appear before or after the integer. Thus, evalua-
tion of this expression results in an error message and abortion of the program:
Integer.parseInt(" 35 ")
Remove the whitespace from the input using String function trim :
Integer.parseInt(" 35 ".trim())
Thus, we should read a line containing an integer, possibly with preceding
/** Read and print two lines from the keyboard. As written, it does not compile. Remove
the comment delimiters around the throws clause on the first line and it will compile. */
public static void readAndProcess () /* throws IOException*/ {
InputStreamReader isr= new InputStreamReader(;
BufferedReader br= new BufferedReader(isr);
String line1= br.readLine();
String line2= br.readLine();
Figure 5.5:
A procedure to read and print two lines from the keyboard
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