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OBJECTIVES
I can:
evaluate arithmetic expressions that use casting
understand that integer values in Java are stored using a finite amount (4 bytes) of memory. Therefore, an int value must be in the range from Integer.MIN_VALUE to Integer.MAX_VALUE inclusive
understand when an expression evaluates to an int value outside of the allowed range, an integer overflow occurs
recognize and use implicit casting
use casting to round to the nearest integer
In Java, type casting is used to convert variables from one type to another.
By casting we don't mean something to do with fishing, but it is a similar idea to casting a pot in clay.
In Java when you cast you are changing the "shape" (or type) of the variable.
The casting operators (int) and (double) are used right next to a number or variable to create a temporary value converted to a different data type.
For example, (double) 1 / 3 will give a double result instead of an int result.
Notice what happens when you:
Line 5: divide an int by an int
Lines 6 & 7: divide a double by an int or an int by a double
Line 8: divide an int casted to a double divided by an int
Java assumes that if you are doing division with integers that you want an integer result and it will truncate ("chop off") and throw away the part after the decimal point.
If you use a mixture of integers (int) and decimal (double) numbers Java will assume that you want a double result.
If there is at least one double in the operation, Java will widen the type of the other operand to a double too and return the result in a double.
If you have integers and you want a double result from some mathematical operation cast one of the integers to a double using (double) as shown above.
ROUNDING
There are a few ways that rounding can be accomplished in Java, but type casting is used for one of them.
Values of type double can be rounded to the nearest integer by adding or subtracting 0.5 and type casting using the (int) operator.
double positiveDouble = 3.249;
int nearestPositiveInt = (int)(positiveDouble + 0.5);
3.249 + 0.5 = 3.749. Java will truncate 3.749 to 3 to give an int result that is properly rounded to the nearest positive integer.
double negativeDouble = -4.652;
int nearestNegativeInt = (int)(negativeDouble - 0.5);
-4.652 - 0.5 = -5.152. Java will truncate -5.152 to -5 to give an int result that is properly rounded to the nearest negative integer.
MAX AND MIN VALUES
Recall that int values are stored using 4 bytes or 32 bits of memory.
2 ^ 32 = 4,294,967,296 possible integer values that can be stored using Java.
Half of these possible values are positive, and the other half are negative.
Therefore, there is an Integer.MAX_VALUE defined as 2,147,483,647 and an Integer.MIN_VALUE defined as -2,147,483,648.
If you try to store any number larger or smaller than these numbers as an int variable, it will result in an integer overflow where an incorrect value could be stored.
I think it's pretty interesting actually. Adding one to the maximum value of an int will result in the minimum value of an int. Subtracting one from the minimum value of an int will result in the maximum value of an int.
SUMMARY
Type casting is used to convert variables from one type to another.
The casting operators (int) and (double) can be used to create a temporary value converted to a different data type.
Casting a double value to an int causes the digits to the right of the decimal point to be truncated (thrown away).
Some programming code causes int values to be automatically cast (widened) to double values.
Values of type double can be rounded to the nearest integer by (int)(x + 0.5) or (int)(x - 0.5) for negative numbers.
Integer values in Java are represented by values of type int, which are stored using a finite amount (4 bytes) of memory. Therefore, an int value must be in the range from Integer.MIN_VALUE to Integer.MAX_VALUE inclusive.
If an expression would evaluate to an int value outside of the allowed range, an integer overflow occurs. This could result in an incorrect value within the allowed range.
EVIDENCE
1) Complete the following Google Form. This form must be 100% correct and includes released AP practice questions. To stop working and return later, hit submit! You can "edit your response" and continue where you left off.
PT.5 Evidence
2) MC Exam Practice: This lesson has additional practice problems which can be found on the MC Exam Practice page with an answer key! Use ctrl + f to search for different objectives throughout the year. You could look at these questions now, or, save these practice questions for later and use them to review! The choice is yours.
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