Given: public class DNASynth { int aCount; int tCount; int cCount; int gCount; void setACount(int cCount) { cCount = cCount; } void setTCount() { this.tCount = tCount; } int setCCount() { return…

The correct answer is A. setAllCounts C. setTCount. There is an error in the provided answer key. The correct answers should be A and E, not A and C. Here is why: setAllCounts (A) clearly modifies fields: the chain assignment aCount = tCount = this.cCount = setGCount(x) writes to three fields, and the call to setGCount(x) also…

Java Object-Oriented Approach

Question

Given:
public class DNASynth {
int aCount;
int tCount;
int cCount;
int gCount;
void setACount(int cCount) {
cCount = cCount;
}
void setTCount() {
this.tCount = tCount;
}
int setCCount() {
return cCount;
}
int setGCount(int g) {
gCount = g;
return gCount;
}
void setAllCounts(int x) {
aCount = tCount = this.cCount = setGCount(x);
}
}
Which two methods modify field values? (Choose two.)

Options

AsetAllCounts
BsetACount
CsetTCount
DsetCCount
EsetGCount

How the community answered

(33 responses)

A
79% (26)
B
3% (1)
D
12% (4)
E
6% (2)

Explanation

There is an error in the provided answer key. The correct answers should be A and E, not A and C. Here is why:

setAllCounts (A) clearly modifies fields: the chain assignment aCount = tCount = this.cCount = setGCount(x) writes to three fields, and the call to setGCount(x) also writes to gCount.
setGCount (E) modifies gCount via gCount = g; - a straightforward field assignment. This is the most obvious example in the class.
setTCount (C) is a trap: this.tCount = tCount looks like a setter, but there is no parameter named tCount, so the right-hand side refers to the field itself. It is a self-assignment (this.tCount = this.tCount) and changes nothing.
setACount (B) is another trap: the parameter is named cCount, shadowing the field. The line cCount = cCount is a self-assignment of the local parameter - no field is touched.
setCCount (D) is a getter in disguise: despite the "set" prefix, it simply returns cCount and modifies nothing.

Memory tip: "set" in a method name means nothing in Java - always check whether the body actually assigns to a field (this.field = param). Watch for parameter shadowing (same name as field without this.) and missing parameters (nothing to assign with).

Topics

#variable shadowing#instance fields#this keyword#field modification

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