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Explanation 7

Not the same as C and C++

Unlike C and C++, which can use an integer numeric expression in the conditional clause of an if statement, Java requires the conditional clause of an if statement to contain an expression that will return a boolean result.

Bad conditional expression

That is not the case in this program, and the following compiler error occurs under JDK 1.3:

Ap031.java:13: incompatible types found : intrequired: boolean if(x - y){

Back to Question 7

Answer 6

D. 6 4 9.3 7.300000000000001

Explanation 6

Postfix increment and decrement operators

This program illustrates the use of the increment (++) and decrement (--) operators in their postfix form.

Behavior of increment operator

Given a variable x , the following two statements are equivalent:

x++; x = x + 1;

Behavior of decrement operator

Also, the following two statements are equivalent:

x--; x = x - 1;

Prefix and postfix forms available

These operators have both a prefix form and a postfix form.

Can be fairly complex

It is possible to construct some fairly complex scenarios when using these operators and combining them into expressions.

In these modules ...

In this group of self-assessment modules, the increment and decrement operators will primarily be used to update control variables in loops.

Inaccurate results

Regarding the program output, you will note that there is a little arithmetic inaccuracy when this program is executed using JDK 1.3. (The same is still true with JDK version 1.7.)

Ideally, the output value 7.300000000000001 should simply be 7.3 without the very small additional fractional part, but that sort of thing often happens whenusing floating types.

Back to Question 6

Answer 5

A. Compiler Error

Explanation 5

Cannot use>with reference variables

The only relational operator that can be applied to reference variables is the == operator.

As discussed in the previous questions, even then it can only be used to determine if two reference variables refer to the same object.

This program produces the following compiler error under JDK 1.3:

Ap029.java:14: operator>cannot be applied to Dummy,Dummy System.out.println(x>y);

Back to Question 5

Answer 4

E. true true

Explanation 4

Two references to the same object

In this case, the reference variables named x and y both refer to the same object. Therefore, when tested for equality, using either the ==operator or the default equals method, the result is true.

Back to Question 4

Answer 3

D. false

Explanation 3

Read question 2

In case you skipped it, you need to read the explanation for the answer to Question 2 before reading this explanation.

Objects appear to be equal

These two objects are of the same type and contain the same values. Whyare they reported as not being equal?

Did not override the equals method

When I defined the class named Dummy used in the programs for Question 2 and Question 3 , I did not override the method named equals .

Therefore, my class named Dummy simply inherited the default version of the method named equals that is defined in the class named Object .

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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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