在java中将标准输出流设置为默认值

Question

I went through the java API documentation.I fiddled with some of the functions and classes and found something strange.The following code I wrote is not setting the standard output stream to the default(System.out). At first,I set the standard output destination to a file and then I tried resetting it but it continues to write in the file.

try
    {

        file=new FileOutputStream("mamamia.txt",true);
        //j=new BufferedOutputStream(file);
        j=new PrintStream (file);
        //byte[] b={49,50,44,67,44,23,57,32};
        //j.write(b,0,5);
        System.setOut(j);
        System.out.println("hey mama mia");
        System.out.println("hello gigs");


        PrintStream j1=new PrintStream (System.out);
        System.setOut(j1);
        System.out.println("Hey bro");

        j.flush();
        file.flush();
        file.close();
         j.close();
    }

'Hey bro' is getting printed in the file.Why is it not going back to default? Prinstream constructor looks for type OutputStream.Since PrintStream is an indirect subclass of OutputStream,I passed System.out directly.It is not showing me any error,the only prob is that it is not going back to the default. Can someone help?

Answer 1

What you are doing is, in great simplification:

stdout = file;
stdout = stdout;

so no surprise it's not set to the original.

You would need to keep the original standard output stream in a temporary variable and then assign it back to System.out . Something like this:

PrintStream originalStdout = System.out;
System.setOut(j);
// do your printing...
// and revert
System.setOut(originalStdout);

Answer 2

System.setOut(j1);

Here you are setting System.out to the printstream it already is linked to, which is the file one.

You should first store the original System.out printstream, then reaffect this original printstream once you're done, like :

try
    {

        file=new FileOutputStream("mamamia.txt",true);
        //j=new BufferedOutputStream(file);
        j=new PrintStream (file);
        //byte[] b={49,50,44,67,44,23,57,32};
        //j.write(b,0,5);
        PrintStream originalStream = System.out;
        System.setOut(j);
        System.out.println("hey mama mia");
        System.out.println("hello gigs");


        System.setOut(originalStream );
        System.out.println("Hey bro");

        j.flush();
        file.flush();
        file.close();
         j.close();
    }