Multiple Choice Question

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Submitted by c-admin on Tue, 05/28/2019 - 04:27

QID:

133

Type:

Multiple Choice Question

Category:

Java Programmer I

Tags:

Operators and Scopes

Question:

Assume that a, b, and c refer to instances of primitive wrapper classes. Which of the following statements are correct?

Note: Although primitive wrapper classes are not explicitly mentioned in the exam objectives, we have seen some candidates get questions on this aspect of wrapper classes.

Select 2 options

A. a.equals(a) will always return true.
B. b.equals(c) may return false even if c.equals(b) returns true.
C. a.equals(b) returns same as a == b.
D. a.equals(b) throws an exception if they refer to instances of different classes.
E. a.equals(b) returns false if they refer to instances of different classes.

Answer and Explanation (Click to expand)

Answer:

A, E

Explanation:

Equals method of a primitive wrapper class ( e.g. java.lang.Integer, Double, Float etc) are

1. symmetric => a.equals(b) returns same as b.equals(a)
2. transitive => if a.equals(b) and b.equals(c) return true, then a.equals(c) returns true.
3. reflexive => a.equals(a) return true.

For example, the following code for the equals method on Integer explains how it works:

public boolean equals(Object obj) {
if (obj instanceof Integer) {
return value == ((Integer)obj).intValue();
}
return false;
}

Q&A Set:

Set 12

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