未检测到循环中的初始化变量

Question

I have this piece of code

    String p4name;
    String p5name;
    if(p1score > p2score && p1score > p3score){
        if(p2score > p3score){
            p1.setWinner(true);
            p2.setWinner(true);
            p3.setWinner(false);
            System.out.println();
            System.out.println();
            System.out.println("**** " + p1.getName() + " and " + p2.getName() + " proceed to 2-Player phase **** ");
            p4name = p1.getName();
            p5name = p2.getName();
        }
        else{
            p1.setWinner(true);
            p2.setWinner(false);
            p3.setWinner(true);
            System.out.println();
            System.out.println();
            System.out.println("**** " + p1.getName() + " and " + p3.getName() + " proceed to 2-Player phase **** ");
            p4name = p1.getName();
            p5name = p3.getName();
        }
    }
    else if(p2score > p1score && p2score > p3score){
        if(p1score > p3score){
            p1.setWinner(true);
            p2.setWinner(true);
            p3.setWinner(false);
            System.out.println();
            System.out.println();
            System.out.println("**** " + p1.getName() + " and " + p2.getName() + " proceed to 2-Player phase **** ");
            p4name = p1.getName();
            p5name = p2.getName();
        }
        else{
            p1.setWinner(false);
            p2.setWinner(true);
            p3.setWinner(true);
            System.out.println();
            System.out.println();
            System.out.println("**** " + p2.getName() + " and " + p3.getName() + " proceed to 2-Player phase **** ");
            p4name = p2.getName();
            p5name = p3.getName();
        }
    }
    else if (p3score > p1score && p3score > p2score){
        if(p1score > p2score){
            p1.setWinner(true);
            p2.setWinner(false);
            p3.setWinner(true);
            System.out.println();
            System.out.println();
            System.out.println("**** " + p1.getName() + " and " + p3.getName() + " proceed to 2-Player phase **** ");
            p4name = p1.getName();
            p5name = p3.getName();
        }
        else{
            p1.setWinner(false);
            p2.setWinner(true);
            p3.setWinner(true);
            System.out.println();
            System.out.println();
            System.out.println("**** " + p2.getName() + " and " + p3.getName() + " proceed to 2-Player phase **** ");
            p4name = p2.getName();
            p5name = p3.getName();
        }
    }
    else {
        System.out.println();
        System.out.println();
        System.out.println("**** It's a tie **** ");
    }

and I attempted to create new objects using the p4name, p5name variable

    Player p4 = new Player(p4name);
    Player p5 = new Player(p5name);

but the cmd said that p4name, p5name is not initialized. Is it because it was initialized in the if/else? Is there any possible ways to overcome this without having to continue the rest of my code in the loop?

Answer 1

I would suggest to extract the following method:

public void setWinners(.. p1, boolean p1Win, .. p2, boolean p2Win, .. p3, boolean p3Win){
                p1.setWinner(p1Win);
                p2.setWinner(p2Win);
                p3.setWinner(p3Win);
                System.out.println();
                System.out.println();
                System.out.println("**** " + p1.getName() + " and " + p2.getName() + " proceed to 2-Player phase **** ");
}

Typically, one should not pass a boolean as a parameter of a method but here IMO it is acceptable:

    String p4name;
    String p5name;
    if(p1score > p2score && p1score > p3score){
        p4name = p1.getName();
        if(p2score > p3score){
            setWinners(p1, true, p2, true, p3, false);
            p5name = p2.getName();
        }
        else{ 
            setWinners(p1, true, p2, false, p3, true);
            p5name = p3.getName();
        }
    }
    else if(p2score > p1score && p2score > p3score){
        if(p1score > p3score){
            setWinners(p1, true, p2, true, p3, false);
            p4name = p1.getName();
        }
        else{
            setWinners(p1, false, p2, true, p3, true);
            p4name = p2.getName();
        }
        p5name = p2.getName();
    }
    else if (p3score > p1score && p3score > p2score){
        if(p1score > p2score){
            setWinners(p1, true, p2, false, p3, true);
            p4name = p1.getName();
        }
        else{
            setWinners(p1, false, p2, true, p3, true);
            p4name = p2.getName();
        }
        p5name = p3.getName();
    }
    else {
        System.out.println();
        System.out.println();
        System.out.println("**** It's a tie **** ");
        return; // Exist the game
    }

        

Answer 2

Most answers so far are suggesting you initialize these variables, and they are all bad advice .

You WANT to leave those variable uninitialized. The advice to pre-initialize them to a value are misleading and bad code style.

Let me first explain that bombshell before I explain what you should be doing in this case.

Why initializing locals is bad in cases like these

Presumably, if you ever get to the place where you execute p5 = new Player(p5Name) , and p5Name has never been set to any value yet, then you've actually got a bug in your program. You do not want a player whose name is the empty string or a blank space.

It is always better that bugs manifest as compilation errors: This means you cannot possibly ship your code with the bug (good thing), the editor will show a red wavy underline precisely at the location where you programmed it (fantastic), and you will be made aware of the fact that you have a bug as you type (marvellous). Leaving the local variable unset gets you exactly this behaviour, which is why it's good to leave them unset. You want the compiler to check that all possible code paths initialize this variable / that all code paths where you end up using p5Name are only reachable via a route that also ends up setting p5Name before you use it.

Contrast to the other option (just initialize them to some throw-away value, like the empty string or a space), which is where the line with the problem (namely, Player p5 = new Player(p5Name) isn't actually where the bug lies (because the bug lies in the control structure above that which has a path where p5Name never gets set), you won't know about the bug until you do a full test run, and a test may not even catch it.

How to do it right

Draw out your control structure as a tree, and figure out which case(s) lead to p5Name being unset. Then add cases to it, or if you feel that all cases are covered, update the code so the compiler follows along with you.

In this case, in your pasted code, if there is any tie, then p4Name and p5Name are unset - and presumably you never wanted that to happen.

It is not clear from your paste what is supposed to happen then, but there are 2 obvious answers that come to mind:

1. Whatever code creates p4 and p5 makes no sense in case there are ties between p1/p2/3, and should therefore never run. If this is the case, your it is a tie! block of code should use control flow to ensure that code then does not run. Either return in the block, or make a method that creates p4/p5, which is only called from the non-it-is-a-tie blocks.

2. The code that creates p4 and p5 can run just fine even in case of ties. If this is what you intended, then update your It is a tie! code block to set p4Name and p5Name to something sensible. Possibly just flip a coin, or just pick one of the pX objects that are involved in the tie and christen them as the value for p4Name and p5Name.

... but there are always exceptions

it is possible that your eyeballs and brain can figure out that it is impossible for a line that uses some local variable x to ever execute for a code path where x is unset, but, that the compiler isn't as smart as you are, and will still complain.

Usually, it is then better to refactor your code so that the compiler does figure it out. Occasionally, however, that does more harm than good (programming, in the end, requires a modicum of experience about how to write maintainable code, styleguides and rules of thumb are merely guidelines, not hard rules, and you'll never get to optimal maintainable code solely by aggressively applying a wide array of style rules no matter how much you invest in writing good style rules, programming just isn't that easy.), If that is the case, then and only then, sure. init that variable to a throwaway, But know that you are missing out on compiler-checked bug-finding. which is a shame: You're basically saying, "The loss of compiler-check here is an evil. but it is the lesser evil compared to how ugly this code is going to get if I attempt to rewrite it so that compiler can figure out that there is no code path where I end up accessing it in an uninitialized state".

Answer 3

Yeah. You need to initialize it to something(blank or null) outside of the if clause. Below change would work.

String p4name = "";
String p5name = "";
if(p1score > p2score && p1score > p3score){

Answer 4

You forgot to initialize the variables, this will give you an error message you need to assign a value to the strings, so the strings are not null. here is the code you need to implement:

String p4name = " ";
String p5name = " ";