7.1 Ap0010: self-assessment, primitive types  (Page 7/9)

Must initialize or assign value to all local variables

Thus, the programmer is responsible for either initializing all local variables, or assigning a value to them before attempting to access their valuewith code later in the program. The good news is that the system won't allow you to compute with garbage left over in memory occupied by variables, either localvariables or member variables.

Back to Question 6

Answer 5 .

B. false

Explanation 5

The boolean type

In this program, the primitive variable named myVar is an instance variable of the type boolean .

What is an instance variable?

An instance variable is a variable that is declared inside a class, outside of all methods and constructors of the class, and is not declared static.Every object instantiated from the class has one. That is why it is called an instance variable.

Cannot use uninitialized variables in Java

One of the great things about Java is that it is not possible to make the mistake of using variables that have not been initialized.

Can initialize when declared

All Java variables can be initialized when they are declared.

Member variables are automatically initialized

If the programmer doesn't initialize the variables declared inside the class but outside of a method (often referred to as member variables as opposed to local variables) , they are automatically initialized to a default value. The default value for a boolean variable is false.

Did you know the boolean default value?

I wouldn't be overly concerned if you had selected the answer A. true, because I wouldn't necessarily expect you to memorize the default initializationvalue.

Great cause for concern

However, I would be very concerned if you selected either C. 1 or D. 0.

Java has a true boolean type

Unlike C++, Java does not represent true and false by the numeric values of 1 and 0. (At least the numeric values that represent true and false are not readily accessible by the programmer.)

Thus, you cannot include boolean types in arithmetic expressions, as is the case in C++.

Back to Question 5

Answer 4 .

• B. 1.7976931348623157E308
• D. 4.9E-324

Explanation 4

Floating type versus integer type

If you missed this one, shame on you!

I didn't expect you to memorize the maximum and minimum values represented by the floating type double, but I did expect you to be able to distinguish betweenthe display of a floating value and the display of an integer value.

Both values are positive

Note that both of the values given above are positive values.

Unlike the integer types discussed earlier, the constants named MAX_VALUE and MIN_VALUE don't represent the ends of a signed number range for type double . Rather, they represent the largest and smallest (non-zero) values that can be expressed by the type.

An indication of granularity

MIN_VALUE is an indication of the degree of granularity of values expressed as type double . Any double value can be treated as either positive or negative.

Two floating types are available

Java provides two floating types: float and double . The double type provides the greater range, or to use another popular terminology, it isthe wider of the two.