Java-如何使用PrintStream / OutputStream打印到命令行

Question

I know we can use PrintStream to print lines to a given file:

    PrintStream output;
    output = new PrintStream("./temp.txt");
    output .println("some output text"); 

However, can we use PrintStream to print lines to the command line ?

I've looked through the Java docs and it seems PrintStream constructor can take a file path or an OutputStream (is there a OutputStream subclass that would print to command line?)

Answer 1

output = new PrintStream(System.out);

or actually,

output = System.out;

Similarly, you can do the same with System.err ... So why don't we just simply use System.out and System.err directly? sout + tab is quite fast to type in IntelliJ

Answer 2

System.out or System.error are already PrintStream and we can use them to print the output to command line without creating a new PrintStream object that you are doing.

Advantage of using this printStream is that you can use System.setOut() or ``System.setErr()` to set the printSteam of your choice

PrintStream output = new PrintStream("./temp.txt");
System.setOut(output); 

Above will override the default Printstream of printing to command line and now calling System.out.println() will print everything in given file(temp.txt)

Answer 3

The PrintStream class provides methods to write data to another stream. To print to command line you can use System.out as out is an object of PrintStream class.

import java.io.*;  
class PrintStreamTest{  
  public static void main(String args[])throws Exception{  
    PrintStream pout=new PrintStream(System.out);  
    pout.println(1900);  
    pout.println("Hello Java");  
    pout.println("Welcome to Java");  
    pout.close();  
  }  
} 

This will give output on command line as:

1900

Hello Java

Welcome to Java