Find a specified string in a file or a file under a certain directory, and print out all lines and line numbers containing the string

This is a written test question. I don’t know how to write it for a while. In the final analysis, the basics are still not enough, and I have to work hard.

First, judge whether it is a directory or a file, and if the directory contains a string by searching all files in the directory.

public class Test{

    public static void search(File file, String str) throws FileNotFoundException{
        Scanner scanner = new Scanner(a,"gbk");//文件编码，可以改成utf-8格式
        int k = 0;
        while(true){
            if(scanner.hasNext()==false)
                break;
            String s = scanner.nextLine();
            k++;
            if(s.contains(x)){
               String a = "文件"+file.getName+"第"+k+"行内容："+s;
               System.out.println(a);
            }
        }
    }
    
    public static void isFileorDirectory(File file, String str) throws FileNotFoundException{
        if(!file.isDirectory()){//判断是否文件
            search(file,str);
        }
        File[] fileNum = file.listFiles();
        if(fileNum==null)
            return;
        for(File file1: fileNum){
            if(file1.isFile()){
                search(file1, str);//是文件，直接查找
            }
            if(file1.isDirectory()){//是目录，则对其目录下的目录或文件继续查找
                isFileorDirectory(file1,str);
            }
        }
        
    }

    public static void main(String[] args){
        isFileorDirectory(new File("目录或者文件名","字符串");
    }
}