Java IO (input output) stream & lt; 1 & gt;

Java IO (input output) stream <1>
I. IO stream Overview 1. IO stream is used for data transmission between devices. 2. Data Operations in Java are performed in a stream-based manner. 3. Classification: 1) data by Operation: byte streams (available in the early stage, can transfer any data) and bytes streams (ASCII code table, Unicode code table <two bytes> ). 2) stream-based: input stream and output stream. 4. abstract base class 1) byte stream: InputStream, OutputStream 2) bytes stream: Reader, Writer II. IO stream instance 1. FileWriter class instance

1 // create a Filewriterdemo Class 2 import java. io. *; 3 4 public class FilewriterDemo {5 6 public static void main (String [] args) throws IOException {7 // A filewritercategory is created, and text.txt 8 FileWriter fw = new FileWriter ("test.txt") is created "); 9 // write data to the memory, only written in the memory 10 fw. write ("abcde"); 11 // refresh the data and write the data into the file 12 fw. flush (); 13 // you can write 14 fw infinitely. write ("haha"); 15 16 fw. flush (); 17 // refresh on disabled 18 fw. close (); 19} 20}

 

2. IO exception

1 // create a Filewriterdemo Class 2 import java. io. *; 3 4 public class FilewriterDemo {5 6 public static void main (String [] args) {7 // defines class 8 FileWriter fw = null outside try; 9 10 try {11 // initialize 12 fw = new FileWriter ("test.txt"); 13 14 fw. write ("abcde"); 15} 16 17 catch (IOException e) {18 19 System. out. println (e. toString (); 20} 21 // when handling exceptions, try to put the closed data stream into finally22 finally {23 24 try {25 // If there are multiple, multiple judgments must be used and cannot be placed in one, such as: 26 // if (fw! = Null & fw = "") and so on 27 if (fw! = Null) 28 29 fw. close (); 30 31} catch (IOException e) {32 33 System. out. println (e. toString (); 34} 35} 36} 37}

 

3. FileRead instance

1 import java. io. *; 2 public class FileRead {3 4 public static void main (String [] args) throws IOException {5 // create a FileReader Class 6 FileReader fd = new FileReader ("test.txt"); 7 // when reading data from a file, at the end of the data, an int-1 is returned, indicating that the end of 8 int ch = 0; 9 while (ch = fd. read ())! =-1) {10 System. out. println ("ch =" + (char) ch); 11} 12/* 13 while (true) {14 int ch = fd. read (); 15 // when ch =-1, the cycle 16 if (ch =-1) 17 break is introduced; 18 // output the read data and forcibly convert it to char type 19 System. out. println ("ch =" + (char) ch); 20} 21 */22 // disable data stream 23 fd. close (); 24 25} 26 27}

 

3.2 read from the array

1 import java. io. *; 2 3 public class FileReadStr {4 5 public static void main (String [] args) throws IOException {6 7 FileReader fd = new FileReader ("test.txt "); 8 // when reading data using arrays, the array is generally defined as a factor of 1024 9 char [] buf = new char [1024]; 10 int num = 0; 11 while (num = fd. read (buf ))! =-1) {12 // from the first entry of the array to the end of the last entry 13 System. out. println (new String (buf, 0, num); 14} 15 16 fd. close (); 17} 18 19}