Working with Files - Advanced Topics in Java: Core Concepts in Data Structures - page 194

Program P7.3
import java.io.*;
public class ReadBinaryFile {
public static void main(String[] args) throws IOException {
DataInputStream in = new DataInputStream(new FileInputStream("num.bin"));
int amt = 0;
try {
while (true) {
int n = in.readInt();
System.out.printf("%d ", n);
++amt;
}
}
catch (IOException e) { }
System.out.printf("\n\n%d numbers were read\n", amt);
} //end main
} //end class ReadBinaryFile
If num.bin contains the output from Program P7.2, then Program P7.3 produces the following output:
25 18 47 96 73 89 82 13 39
9 numbers were read
The new statement in Program P7.3 is this:
DataInputStream in = new DataInputStream(new FileInputStream("num.bin"));
A data input stream lets a program read primitive Java data types from an input stream that was created as a data
output stream. A file input stream is an input stream for reading data from a file. The following constructor creates an
input stream connected to the file num.bin :
new FileInputStream("num.bin")
The following are some of the methods in the DataInputStream class:
int readInt() //read 4 input bytes and return an int value
double readDouble() //read 8 input bytes and return a double value
char readChar() //read a char as a 2-byte value
void readFully(byte[] b) //read bytes and store in b until b is full
float readFloat() //read 4 input bytes and return a float value
long readLong() //read 8 input bytes and return a long value
int skipBytes(int n) //attempts to skip n bytes of data;
//returns the number actually skipped
Generally speaking, these methods are used to read data that was written using the corresponding “write”
methods from DataOutputStream .
Note the use of try...catch to read numbers until end-of-file is reached. Recall that there is no “end-of-data”
value in the file, so we can't test for this. The while statement will read from the file continuously. When the end-of-
file is reached, an EOFException is thrown. This is a subclass of IOException and so is caught.
The catch block is empty, so nothing happens there. Control goes to the following statement, which prints the
amount of numbers read.