1. EEC 484/584 Computer Networks
Java Tutorial #2: Java IO
Wenbing Zhao
Cleveland State University
Materials taken from:

2. EEC484/584 Computer Networks
Java IO
To do Java IO, need to
Import java.io.*
System
InputStreamReader
BufferedReader
File
BufferedWriter
FileReader
FileWriter
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EEC484/584 Computer Networks

3. EEC484/584 Computer Networks
System
System.in: standard input (of type: InputStream)
System.out: standard output
import java.io.*;
public class TrivialApplication {
public static void main ( String args[] ) throws IOException{
//reads one byte as an integer from standard in
int ch = System.in.read();
System.out.println((char)ch); // print to standard out }; }
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EEC484/584 Computer Networks

4. EEC484/584 Computer Networks
InputStreamReader
InputStreamReader: a bridge from byte streams to character streams, i.e., it reads bytes and decodes them into characters
Constructor: InputStreamReader(InputStream in)
Methods: close(); read(); etc.
import java.io.*;
public class TrivialApplication {
public static void main ( String args[] ) throws IOException{
InputStreamReader input = new InputStreamReader(System.in);
int ch = input.read();
System.out.println((char)ch); // print to standard out }; }
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EEC484/584 Computer Networks

5. EEC484/584 Computer Networks
BufferedReader
BufferedReader: is used to improve IO efficiency, i.e., it may read more bytes from the underlying stream than necessary to satisfy current read operation
Constructor: BufferedReader(Reader in)
Methods: close(); read(); readLine(); etc.
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
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EEC484/584 Computer Networks

6. EEC484/584 Computer Networks
File
File: used to create a file with designated filename
File inputFile = new File("testFile.txt");
// relative path, in current working directory
File outputFile = new File("/home/users/2p92/outFile.txt");
// absolute path, separators OS dependent
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EEC484/584 Computer Networks

7. EEC484/584 Computer Networks
BufferedWriter
Make write operation more efficient: allows for one writing step by providing data output storage which can then be outputted efficiently
Constructor: BufferedWriter(Writer out);
Methods: close(); flush(); newLine(); write(int c), etc.
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EEC484/584 Computer Networks

8. EEC484/584 Computer Networks
FileReader
Allows an application to gain access to character input from file
Constructor: FileReader(File file)
Methods: close(); read(); etc.
File inputFile = new File("test.dat");
FileReader Joe = new FileReader(inputFile);
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EEC484/584 Computer Networks

9. EEC484/584 Computer Networks
FileWriter
Allows an application to place character output in the designated file
Constructor: FileWriter(File file);
Methods: close(); flush(); write(); etc.
File inputFile = new File("test.dat");
FileReader Joe = new FileReader(inputFile);
File outputFile = new File("out.dat");
FileWriter out = new FileWriter(outputFile);
int c;
While ((c = joe.read() !=-1){
out.write(c); }
joe.close(); out.close();
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EEC484/584 Computer Networks

10. EEC484/584 Computer Networks
A Useful Example
public class IOTest {   public static void main(String[] args) throws IOException {       BufferedReader br =
new BufferedReader(new FileReader(new File("iotest.dat")));       BufferedWriter bw =
new BufferedWriter(new FileWriter(new File("iotestout.dat")));       while(true) { String s = br.readLine();      if(null == s) break;           bw.write("Out: "+s); bw.newLine();       }       bw.flush();       br.close();       bw.close();   } }
6/4/2019
EEC484/584 Computer Networks