我试图制作一个程序，但控制台仍然显示“线程“main”java.lang.NullPointerException中的异常”，我不知道出了什么问题

Question

程序应该是这样工作的：

首先它从用户那里获得 SENTENCE（字符串）和 MUTATION 因子（double）。然后它将字符串 SENTENCE 更改为字符数组 (ARRAY 1)。之后，它创建了 5 个新的字符数组，其长度等于 ARRAY 1 的长度。它们中的每一个都充满了随机字符（只有字母和空格）。然后程序选择与 ARRAY 1 最相似的 5 个数组中的一个。获胜者“乘”到接下来的 5 个数组中。在它们中的每一个中，程序都会验证是否符合 ARRAY 1。如果字符适合 ARRAY 1 中的字符，则程序不会更改它。如果 char 不适合 ARRAY 1 中的那个，那么它是否会发生变异（根据 MUTATION 因子和随机概率）。然后程序选择一个与 ARRAY 1 最相似的数组，获胜者“multiplies”等。程序工作直到程序制作的数组与 ARRAY 1 相同。'Counter'（静态 int）计算具有数组的“代”数在程序制作正确的数组之前通过。

我怀疑最后一种方法可能有问题。但我真的不知道它是什么。这是我写的代码：

static int counter;
public static void main(String[] args) {

    Scanner skaner = new Scanner(System.in);
    String sentence = skaner.nextLine();
    double mutation = Double.parseDouble(skaner.nextLine());

//
        ArrayList<char[]> candidates = Draw(ChangeIntoChars(sentence), mutation);
        char[] candidate = ChooseTheBestOne(candidates,
                ChangeIntoChar(sentence));
        String result = CheckAndDraw(candidate, ChangeIntoChars(sentence),
                mutation);
        System.out.print(result);
        System.out.println();
        System.out.print(counter);
}

    public static char[] ChangeIntoChars (String sentence) {

        char[] chars = sentence.toCharArray();
        return chars;
    }



    public static ArrayList<char[]> Draw (char [] chars, double mutation) {

        char [] random1 = new char [chars.length];
        char [] random2 = new char [chars.length];
        char [] random3 = new char [chars.length];
        char [] random4 = new char [chars.length];
        char [] random5 = new char [chars.length];

        Random r = new Random();


        for (int i=0; i<random1.length; i++) {
            if          (random1[i]==chars[i]) {}
            else        {double p = Math.random();
                        if (mutation>p){
                String alphabet = "aąbcćdeęfghijklłmnńoópqrsśtuwxyzżź ";
                random1[i]=(alphabet.charAt(r.nextInt(alphabet.length())));
                        }
                        else {}
                        }}

        for (int i=0; i<random2.length; i++) {
            if      (random2[i]==chars[i]) {}
            else        {double p = Math.random();
                        if (mutation>p){
                String alphabet = "aąbcćdeęfghijklłmnńoópqrsśtuwxyzżź ";
                random2[i]=(alphabet.charAt(r.nextInt(alphabet.length())));
                        }
                        else {}
                        }}

        for (int i=0; i<random3.length; i++) {
            if      (random3[i]==chars[i]) {}
            else        {double p = Math.random();
                        if (mutation>p){
                String alphabet = "aąbcćdeęfghijklłmnńoópqrsśtuwxyzżź ";
                random3[i]=(alphabet.charAt(r.nextInt(alphabet.length())));
                        }
                        else {}
                        }}

        for (int i=0; i<random4.length; i++) {
            if      (random4[i]==chars[i]) {}
            else        {double p = Math.random();
                        if (mutation>p){
                String alphabet = "aąbcćdeęfghijklłmnńoópqrsśtuwxyzżź ";
                random4[i]=(alphabet.charAt(r.nextInt(alphabet.length())));
                        }
                        else {}
                        }}

        for (int i=0; i<random5.length; i++) {
            if      (random5[i]==chars[i]) {}
            else        {double p = Math.random();
                        if (mutation>p){
                String alphabet = "aąbcćdeęfghijklłmnńoópqrsśtuwxyzżź ";
                random5[i]=(alphabet.charAt(r.nextInt(alphabet.length())));
                        }
                        else {}
                        }}


        ArrayList<char[]> candidates = new ArrayList<char[]>();
        candidates.add(random1);
        candidates.add(random2);
        candidates.add(random3);
        candidates.add(random4);
        candidates.add(random5);

        return candidates;
    }
    public static char [] ChooseTheBestOne(ArrayList<char[]>candidates,char[]chars) {

        char [] number1 = candidates.get(0);
        char [] number2 = candidates.get(1);
        char [] number3 = candidates.get(2);
        char [] number4 = candidates.get(3);
        char [] number5 = candidates.get(4);

        int j = 0;
        for (int i=0; i<number1.length; i++){
            if (number1[i]==chars[i]){
                j++;}
            }

        int k = 0;
        for (int i=0; i<number2.length; i++){
            if (number2[i]==chars[i]){
                k++;}
            }

        int l = 0;
        for (int i=0; i<number3.length; i++){
            if (number3[i]==chars[i]){
                l++;}
            }

        int m = 0;
        for (int i=0; i<number4.length; i++){
            if (number4[i]==chars[i]){
                m++;}
            }

        int n = 0;
        for (int i=0; i<number5.length; i++){
            if (number5[i]==chars[i]){
                n++;}
            }

        int [] whosTheWinner = {j,k,l,m,n};
        int max = 0;
        char[] winner = null;
        for (int x=0; x<whosTheWinner.length; x++) {
            if (whosTheWinner[x]> max) {max = whosTheWinner[x];
                if  (x==0) {winner = number1;}
                else if (x==1) {winner = number2;}
                else if (x==2) {winner = number3;}
                else if (x==3) {winner = number4;}
                else if (x==4) {winner = number5;}

        }}
        counter++;
        return winner ;
        }
    public static String CheckAndDraw (char[]winner,char[]chars,double mutation){
        int i = 0;
        String end = "This is not what I meant.";

        boolean success;


        if (winner[i]==chars[i]){
            success = true;
            end = "END";
        }
        else {success = false;}


        while (success!=true){

            ArrayList<char[]> resultsOfTheDraw = Draw(winner, mutation);
            winner = ChooseTheBestOne(resultsOfTheDraw, chars);

            }



        return end;

        }
    }

Answer 1

您的问题是，在方法 ChooseTheBestOne() 中，在方法末尾的 if-else 阶梯中，有时没有任何条件为真，因此 winner 仍然为空。您需要在该阶梯中放置一个 else 子句，将某些内容分配给 winner。