7.1 Ap0010: self-assessment, primitive types  (Page 6/9)

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Answer 9 .

D. 6.0

Explanation 9

Declare and initialize two local variables

This program declares and initializes two local variables, one of type double and the other of type int . Each variable is initialized with the integer value 3.

Automatic conversion to floating type double

However, before the value of 3 is stored in the double variable, it is automatically converted to type double .

Automatic conversion in mixed-type arithmetic

Numeric addition is performed on the two variables. Whenever addition is performed between a floating type and an integer type, the integer type isautomatically converted to a floating type and floating arithmetic is performed.

A floating result

This produces a floating result. When this floating result is passed to the println method for display, a decimal point and a zero are displayed to indicate a floating type, even though in this case, the fractional part of theresult is zero.

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Answer 8 .

A. Compiler Error

Explanation 8

Initialize boolean variable to true

This program declares and initializes a boolean variable with the value true . Then it attempts to add the literal value 1 to the value stored in the boolean variable named myVar .

Arithmetic with boolean values is not allowed

As mentioned earlier, unlike C++, boolean types in Java cannot participate in arithmetic expressions.

Therefore, this program will not compile. The compiler error produced by this program under JDK 1.3 reads partially as follows:

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Answer 7 .

D. false

Explanation 7

Format for variable initialization

This program declares a local boolean variable and initializes it to the value true . All variables, local or otherwise, can be initialized in this manner provided that the expression on the right of the equal sign evaluates toa value that is assignment compatible with the type of the variable. (I will have more to say about assignment compatibility in a future module) .

Value is changed before display

However, before calling the println method to display the initial value of the variable, the program uses the assignment operator (=) to assign the value false to the variable. Thus, when it is displayed, the value is false .

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Answer 6 .

A. Compiler Error

Explanation 6

A local boolean variable

In this program, the primitive variable named myVar is a local variable belonging to the method named printBoolean .

Local variables are not automatically initialized

Unlike instance variables, if you fail to initialize a local variable, the variable is not automatically initialized.

Cannot access value from uninitialized local variable

If you attempt to access and use the value from an uninitialized local variable before you assign a value to it, you will get a compiler error.The compiler error produced by this program under JDK 1.3 reads partially as follows: