7.2 Ap0020: self-assessment, assignment and arithmetic operators  (Page 9/11)

The good news

The good news about doing arithmetic using operands of integer types is that as long as the result is within the allowable value range for the wider of theinteger types, the results are exact (floating arithmetic often produces results that are not exact) .

The bad news

The bad news about doing arithmetic using operands of integer types is that when the result is not within the allowable value range for the wider of theinteger types, the results are garbage, having no usable relationship to the correct result (floating arithmetic has a high probability of producing approximately correct results, even though the results may not be exact).

For this specific case ...

As you can see by the answer to this question, when a value of 2 was added to the largest positive value that can be stored in type int , the incorrect result was a very large negative value.

The result is simply incorrect. (If you know how to do binary arithmetic, you can figure out how this happens.)

No safety net in this case -- just garbage

Furthermore, there was no compiler error and no runtime error. The program simply produced an incorrect result with no warning.

You need to be especially careful when writing programs that perform arithmetic using operands of integer types. Otherwise, your programs mayproduce incorrect results.

Back to Question 6

Answer 5

C. 4.294967294E9

Explanation 5

Mixed-type arithmetic

This program illustrates the use of arithmetic operators with operands of different types.

Declare and initialize an int

The method named doMixed declares a local variable of type intnamed myIntVar and initializes it with the largest positive value that can be stored in type int .

Evaluate an arithmetic expression

An arithmetic expression involving myIntVar is evaluated and the result is passed as a parameter to the println method where it is displayed on the computer screen.

Multiply by a literal double value

The arithmetic expression uses the multiplication operator (*) to multiply the value stored in myIntVar by 2.0 (this literal operand is type double by default) .

Automatic conversion to wider type

When arithmetic is performed using operands of different types, the type of the operand of the narrower type is automatically converted to the type of theoperand of the wider type, and the arithmetic is performed on the basis of the wider type.

Result is of the wider type

The type of the result is the same as the wider type.

In this case ...

Because the left operand is type double , the int value is converted to type double and the arithmetic is performed as type double .

This produces a result of type double , causing the floating value 4.294967294E9 to be displayed on the computer screen.

Back to Question 5

Answer 4

C. 2147483647

Explanation 4

Uses a cast operator

This program, named Ap013.java , differs from the earlier program named Ap012.java in one important respect.

This program uses a cast operator to force the compiler to allow a narrowing conversion in order to assign a double value to an int variable.

The cast operator