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Day 4: Object Lessons
NOTES AND CORRECTIONS
SOURCE FILES
READER QUESTIONS
- Q: The length() and charAt() methods in Listing
4.3 don't appear to make sense. If length() says that a string
is 48 characters long, shouldn't the characters be numbered from 1 to
48 when charAt() is used to display characters in the string?
A: The two methods look at strings a little differently. The length() method counts the characters in the
string, with the first character counting as 1, the second as 2, and so on.
The string Charlie Brown has 13 characters. The charAt() method considers the first character in the
string to be located at position number 0. This is the same numbering
system used with array elements in Java. The string Charlie Brown
has characters ranging from position 0 -- the letter "C" --
to position 12 -- the letter "n".
- Q: I've got the following question about the line found in
Day 4; Page 103: "The exception is casting integers to
floating point values -- casting an int or a long to a float,
or a long to a double can cause some loss of
precision."
How can an integer lose precision when it doesn't have it to begin
with (in other words, it's not a real number)? -- P. R.
A: The loss of precision occurs because integer types can hold
more whole numbers than floating-point types. For this reason, you run
into a loss of precision when casting very large int and long
values to float and very large long values to double.
Both int and float are 32-bit
values in Java. The int primitive data type can represent 2.14
trillion different whole numbers, but float can only represent
around 16.78 million whole numbers, because it also has to represent
other values. When you cast an int value higher than 16,777,216
to a float, because of how Java applies the rules of
floating-point arithmetic, the int value will be converted to
the closest whole number that float can represent.
To see this in action, write an application
with the following code:
int i = 2000000000;
float one = i;
float two = i + 5;
if (one == two)
System.out.println("Numbers are equal.");
else
System.out.println("Numbers are not
equal.");
This will display the string
"Numbers are equal." If you change the first line to int
i = 16777216, the code will display the string "Numbers
are not equal."
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