JAVA：为什么 Eclipse 将我的第二个 else-if 语句称为“死代码”？

Question

I am writing a code in JAVA on Eclipse IDE, and I am having a problem with my if-else statement. From my third outer "if", I have two "else-if" blocks, and Eclipse is calling my second "else-if" a dead code and skips it -- I checked it using Eclipse debugger, but I don't know why. Eclipse keeps suggesting me to delete the second else-if statement, which significantly changes my code.

Please let me know if there is any other information that I can add, and thanks in advance for all the help!

Here is the code:

public static void eachCycleUni (Queue processes, int numProcesses, Process[] allProcesses, Process[] original) {   
    Queue<Process> readyProcesses = new LinkedList<Process>();      //Stores processes that are ready

    for (int p = 0; p < allProcesses.length; p++) {
        Process currentProcess = allProcesses[p];
        while (terminatedProcesses != numProcesses) {
            //Nothing --> Nothing or Nothing --> currentRunning
            if (currentRunning == null && currentBlocked == null) {
                ....
            }
            //currentRunning --> --, or currentRunning --> currentBlocked, or currentRunning --> terminated
            else if (currentRunning.CPUburstRemaining != 0 && currentBlocked == null) {
                ...
            }
            //THIS ELSE-IF
            else if (currentBlocked.IOburstRemaining != 0 && currentRunning == null) {
                ...
            }
            cycleNumber++;
        }
    }
}

Answer 1

The relevant if and else-if checks are:

if (currentRunning == null && currentBlocked == null) {
   ...
}
else if (currentRunning.CPUburstRemaining != 0 && currentBlocked == null) {
   ...
}
else if (currentBlocked.IOburstRemaining != 0 && currentRunning == null) {
   ...
}

Your first if-checks will check that both currentRunning and currentBlocked are both null .

If this is not the case, you will check if currentBlocked is null and using currentRunning.CPUburstRemaining implicitly means currentRunning cannot be null (otherwise a NullPointerException would have been given).

After these two checks we therefore know that currentRunning can never be null anymore, because it would either have entered the first if -statement, or would have given a NullPointerException at the currentRunning.CPUburstRemaining in the first else if -block.

Because of that, your && currentRunning == null part of your else if (currentBlocked.IOburstRemaining != 0 && currentRunning == null) will always be falsey, so the IDE sees this as dead code.