Java IO.pdf - Nguyen Dang Binh

Java I/O
This whole class is just a wrapper around an int position, which is set by the constructor and
the setIndex() mutator method. It's returned by the getIndex() method. As a
NumberFormat parses a string, it updates the associated ParsePosition's index. Thus, when
passed into a parse() method, the ParsePosition contains the index where parsing will
begin. When the parse() method returns, the ParsePosition contains the index
immediately after the last character parsed. If parsing fails, the parse position is unchanged.
Some number formats can only read integers, not floating point numbers. The
isParseIntegerOnly() method returns true if this is the case, false otherwise.
public boolean isParseIntegerOnly()
public void setParseIntegerOnly(boolean value)
The setParseInteger() method lets you specify that the format should only parse integers.
If a decimal point is encountered, then parsing should stop.
Example 16.8 is a simple program of the sort that's common in CS 101 courses. The
assignment is to write a program that reads a number entered from the command line and
prints its square root. Successive numbers are read until a negative number is entered, at
which point the program halts. Although this is a very basic exercise, it's relatively complex
in Java, because Java separates string parsing from basic I/O. Nonetheless, while it may not
be suitable for the first week's homework, students should be able to handle it by the end of
the semester.
Example 16.8. RootFinder
import java.text.*;
import java.io.*;
public class RootFinder {
public static void main(String[] args) {
Number input = null;
try {
BufferedReader br = new BufferedReader(new
InputStreamReader(System.in));
NumberFormat nf = NumberFormat.getInstance();
while (true) {
System.out.println("Enter a number (-1 to quit): ");
String s = br.readLine();
try {
input = nf.parse(s);
}
catch (ParseException e) {
System.out.println(s + " is not a number I understand.");
continue;
}
double d = input.doubleValue();
if (d < 0) break;
double root = Math.sqrt(d);
System.out.println("The square root of " + s + " is " + root);
}
}
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