Question

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Compiler complains about “missing return statement” even though it is impossible to reach condition where return statement would be missing

The following method in Java compiles fine.

public String temp() {
    while(true) {
        if(true) {
            // Do something.
        }
    }
}

The method has an explicit return type which is java.lang.String with no return statement though it compiles fine. The following method however fails to compile.

public String tempNew() {
    if(true) {
        return "someString";
    }        
}

A compile-time error is issued indicating “missing return statement” even though the condition specified with the if statement is always true (it has a boolean constant that is never going to be changed neither by reflection). The method must be modified something like the following for its successful compilation.

public String tempNew() {
    if(true) {
        return "someString";
    } else {
        return "someString";
    }
}

or

public String tempNew() {
    if(true) {
        return "someString";
    }

    return "someString";
}

Regarding the first case with the while loop, the second case appears to be legal though it fails to compile.

Is there a reason in the second case beyond one of the compiler’s features.

Answer 1

Because it is dead code. The dead code analysis is done in a separate pass to the method return analysis, which does some more in-depth analysis that looks inside branch conditions.