如何读取文本文件并将其打印到控制台窗口？ 爪哇

Question

I would like to read an entire text file and store its entire contents into a single string. Then I would like to print the string to the console window. I tried this:

import java.util.Scanner;
import java.io.*;

public class WritingTextFiles{

    public static void main (String [] args) throws IOException{
        FileWriter fw= new FileWriter("testing.txt");  
        Scanner in= new Scanner (System.in);
        String testwords=in.nextLine();  
        fw.write(testwords);  
        BufferedReader r = new BufferedReader( new FileReader( "testing.txt" ) );  
        System.out.print(r);  
        fw.close();  
    }
}

The only thing that is printed to the console window is java.io.BufferedReader@18fb397.

Can anyone explain this to a newbie like me? I have very little experience but I am certainly willing to learn. I am open to any and all suggestions. Thanks in advance!

Answer 1

The reason that java.io.BufferedReader@18fb397 is printed to the console is because you give the reference of the buffered reader as an argument to print, and not the string you want to print.

BufferedReader r = new BufferedReader( new FileReader( "testing.txt" ) );
System.out.print(r);

should be:

BufferedReader r = new BufferedReader( new FileReader( "testing.txt" ) );
String s = "", line = null;
while ((line = r.readLine()) != null) {
    s += line;
}
System.out.print(s);

Notice we actually read the lines of the file and store it in a temporary variable, then we append this variable to s. Then we print s, and not the BufferedReader.

On a final note, it is wise to close a file when your done, you do call fw.close(), but you should have called it directly after writing the testwords. This is to make sure that the FileWriter has actually written the string.

Answer 2

If it's a relatively small file, a one-line Java 7+ way to do this is:

System.out.println(new String(Files.readAllBytes(Paths.get("testing.txt"))));

If you just want to read it into a String, that's also simple:

String s = new String(Files.readAllBytes(Paths.get("testing.txt")));

See https://docs.oracle.com/javase/7/docs/api/java/nio/file/package-summary.html for more details.

Cheers!