Standard input / output stream

We usually use Scanner The following method is used to input data from the keyboard , But it is also a very meaningful thing to find out its essence .

Its bottom layer still uses byte input stream .

In this way, it is connected with the knowledge of flow .

Standard output stream

public class PrintStreamextends FilterOutputStreamimplements Appendable, Closeable

PrintStream Added functionality for other output streams , So that they can easily print various data value representations . It also provides two other functions . Unlike other output streams ,PrintStream Never throw IOException; It is , Exceptions can only be set through checkError The internal logo of the method test . in addition , In order to automatically refresh , You can create a PrintStream; This means that you can write byte Array is automatically called after flush Method , One of the println Method , Or write a newline character or byte (‘\n’). PrintStream All characters printed are converted to bytes using the platform's default character encoding . In the case of writing characters instead of bytes , You should use PrintWriter class .

Some construction methods

PrintStream(File file) Create a new print stream with the specified file and no automatic line refresh . PrintStream(File file, String csn) Create a new print stream with the specified file name and character set without automatic line refresh . PrintStream(OutputStream out) Create a new print stream . PrintStream(OutputStream out, boolean autoFlush) Create a new print stream . PrintStream(OutputStream out, boolean autoFlush, String encoding) Create a new print stream . PrintStream(String fileName) Create a new print stream with the specified file name without automatic line refresh . PrintStream(String fileName, String csn) Create a new print stream with the specified file name and character set without automatic line refresh .

So the message we get is , We can determine whether to refresh automatically according to the Boolean value in the parameter , In addition, you can also specify the encoding .

This is the same as the standard input stream System The format defined in the class is the same . Bottom words , In fact, it is also a byte stream . Simply look at how to use .

 // Standard output stream 
        PrintStream out = System.out;
        out.print("hello");// Output on the console 

But you can also output to a file , That is to input data into a file .

  // Byte print stream 
        PrintStream ps = new PrintStream("E:\\java_doc\\src\\io_demo\\jgdabc.txt");
        ps.write(97);// Use parent methods 
        ps.print(97);// Use your own method 
        ps.close();
       // Character print stream 
        PrintWriter pW = new PrintWriter("E:\\java_doc\\src\\io_demo\\jgdabc.txt");
        pW.write("hello");
        pW.flush();
        pW.println("Hello");
        pW.flush();
        PrintWriter pw = new PrintWriter(new FileWriter("E:\\java_doc\\src\\io_demo\\jgdabc.txt"),true);// Will automatically refresh 
        pw.println("Hello");
        pw.println("world"