java - 使用正则表达式 Java 搜索字母

Question

public static void main(String[]args){

**exp("^[a[k][t][l]]{6}$"); //line 9**
exp("^(bEt).*(oc)$");
exp("^(bEt)$");
exp("^(a).*");
exp("bEt(oc)*");
exp("^(bEt).*");
exp [baba][bebe][bibi][bobo][bubu][fafa][fefe][fofo][fufu]

}

public static void exp(String uttryck){
    int counter = 0;
    File fil = new File("Walta_corpus1.txt");
    Scanner sc = null;
    try{
        sc = new Scanner(fil);
    }
    catch(FileNotFoundException foo){
    }
    **String word = sc.next();** line 28
    Pattern pattern = Pattern.compile(uttryck);
    Matcher matcher = pattern.matcher(word);



    while(word != null){
        if(matcher.find()){
            counter++;
            System.out.println(word);
            }

        if(sc.hasNext()){
            word=sc.next();
            matcher = pattern.matcher(word);
            }
        else
            word = null;
    }
    System.out.println(counter);

}

我需要帮助解决的问题是:

    Exception in thread "main" java.lang.NullPointerException
at raknare.exp(raknare.java:28)
at raknare.main(raknare.java:9)

我尝试了很多，但没有任何效果。

Answer 1

检查下面的代码:

public static void exp(String uttryck) throws FileNotFoundException{
// .....
try{
    sc = new Scanner(fil);
}
catch(FileNotFoundException foo){
    // if scanner throws exception, sc is null
    foo.printStackTrace(); // add this method call and check.
    throw foo; //rethrow exception to caller
}
String word = sc.next(); // if catch is executed, sc will give NullPointerException

//.....
}

如果您得到FileNotFoundException，那么您将在上面一行得到NullPointerException，因为您在捕获异常FileNotFoundException后继续。