"Local variable is redundant" using Java

Question

Why is the following giving me a "local variable is redundant error"?

public double depreciationAmount() {
    double depreciationAmount = (cost * percentDepreciated);
    return depreciationAmount;
}

Answer 1

Why is the following giving me a "local variable is redundant error"?

Because you can trivially write this without using a local variable.

public double depreciationAmount() {
    return cost * percentDepreciated;
}

Hence the local variable is deemed to be unnecessary / redundant by the checker.

---

However, I surmise that this is not a compiler error. It might be a compiler warning, or more likely it is a style checker or bug checker warning. It is something you could ignore without any risk to the correctness of your code ... as written.

Also, I would predict that once that the code has been JIT compiled (by a modern Hotspot JIT compiler ...) there would be no performance difference between the two versions.

---

I won't attempt to address the issue as to whether the warning is appropriate¹. If you feel it is inappropriate, then "Local variable is redundant" using Java explains how to suppress it.

---

^{1 - Except to say that it is too much to expect current generation style checkers to know when so-called explaining variables are needed. First you'd need to get a statistically significant2 group of developers to agree on measurable3 criteria for when the variables are needed, and when they aren't.
2 - Yea, I know. Abuse of terminology.
3 - They must be measurable, and there needs to be consensus on what the thresholds should be if this is to be implemented by a checker.}

Answer 2

Although not the case here, if having a redundant local variable is desired (I've had one time where this was the case - without getting into specifics), here's how to suppress this specific warning.

@SuppressWarnings("UnnecessaryLocalVariable")
public double depreciationAmount() {
    double depreciationAmount = (cost * percentDepreciated);
    return depreciationAmount;
}