Question

Can anyone explain what the trade off (even if it’s negligible) would be between using if, if else, or switch in a sizable block of code similar to the following? Is the situation different if it were comparing a String or another Object instead of an int? The examples are in Java but it is meant as a general question.

EDIT

As several answers stated, a switch is going to be faster and should probably be used if there are more than a few cases. However, nobody has commented on if vs if else when in a long chain like this. What sparked this question is that I am frequently creating these blocks where a switch can’t be used because most of the cases require multiple expressions. I guess excluding the else feels sloppy, but it isn’t really necessary so why include it?

public String getValueString(int x) {
    if (x == 1) return "one";
    if (x == 2) return "two";
    if (x == 3) return "three";
    if (x == 4) return "four";
    ...
    return null;
}

VS

public String getValueString(int x) {
    if (x == 1) return "one";
    else if (x == 2) return "two";
    else if (x == 3) return "three";
    else if (x == 4) return "four";
    ...
    return null;
}

VS

public String getValueString(int x) {
    switch(x) {
        case 1: return "one";
        case 2: return "two";
        case 3: return "three";
        case 4: return "four";
        ...
    }
    return null;        
}

Answer 1

If you have a lot of cases, then the switch approach is the preferred method. The reason is because the first two requires essentially a linear search through all the if-statements. So it is O(N) to the number of cases you have.

On the other hand, switch statements are optimized differently and can be either O(log(N)) or even O(1) for finding that correct case.

---

How can the compiler achieve O(log(N)) or even O(1)?

• Binary search of the case values will allow it to be done in O(log(N)).
• If the case values are dense enough, the compiler may even use a jump table indexed by the case variable. In that case it is O(1).