Read a File in Java which reads floating point radii

The java.io.DataInputStream and java.io.DataOutputStream classes read and write primitive Java data types and strings in a specified machine-independent format. Generally you use a DataInputStream to read data written by a DataOutputStream. By using data streams, you guarantee that the data you write on one system can be read by Java programs on other systems.
There are twelve write methods in the DataOutputStream class.

The DataOutputStream has these methods:

public DataOutputStream(OutputStream out)
 
public synchronized void write(int b) throws IOException
 
public synchronized void write (byte b[], int offset, int length) throws IOException
 
public void flush() throws IOException
 
public final void writeBoolean(boolean v) throws IOException
 
public final void writeByte(int v) throws IOException
 
public final void writeShort(int v) throws IOException
 
public final void writeChar(int v) throws IOException

public final void writeInt(int v) throws IOException
 
public final void writeFloat(float v) throws IOException
 
public final void writeDouble(double v) throws IOException
 
public final void writeBytes(String s) throws IOException
 
public final void writeChars(String s) throws IOException
 
public final void writeUTF(String str) throws IOException
 
public final int size()

There are twelve corresponding read methods in the DataInputStream Class.

public DataInputStream(InputStream in)
 
public final int read(byte b[]) throws IOException
  
public final int read(byte b[], int offset, int length) throws IOException
  
public final void readFully(byte b[]) throws IOException
  
public final void readFully (byte b[], int offset, int length) throws IOException
  
public final int skipBytes(int n) throws IOException
 
public final boolean readBoolean() throws IOException
  
public final byte readByte() throws IOException

In Java SE 17, the DataInputStream class is part of the java.io package and provides methods to read primitive data types and strings from an input stream.
List of read Methods in DataInputStream

1. int read()
   • Reads the next byte of data from the input stream.
   • Returns: The byte read, or -1 if the end of the stream is reached.
   • Throws: IOException
2. int read(byte[] b)
   • Reads up to b.length bytes of data into an array.
   • Returns: The number of bytes read, or -1 if the end of the stream is reached.
   • Throws: IOException
3. int read(byte[] b, int off, int len)
   • Reads up to len bytes into an array starting from index off.
   • Returns: The number of bytes read, or -1 if the end of the stream is reached.
   • Throws: IOException
4. boolean readBoolean()
   • Reads one byte and returns true if the byte is nonzero, false otherwise.
   • Throws: IOException
5. byte readByte()
   • Reads one byte and returns it as a byte.
   • Throws: IOException, EOFException
6. char readChar()
   • Reads two bytes and returns a char.
   • Throws: IOException, EOFException
7. double readDouble()
   • Reads eight bytes and returns a double.
   • Throws: IOException, EOFException
8. float readFloat()
   • Reads four bytes and returns a float.
   • Throws: IOException, EOFException



 

9. void readFully(byte[] b)
   • Reads b.length bytes into the provided array.
   • Throws: IOException, EOFException
10. void readFully(byte[] b, int off, int len)
    • Reads exactly len bytes into an array starting from off.
    • Throws: IOException, EOFException
11. int readInt()
    • Reads four bytes and returns an int.
    • Throws: IOException, EOFException
12. String readLine() (Deprecated)
    • Reads a line of text (terminated by \n, \r, or \r\n).
    • Returns: The read line as a String, or null if EOF is reached.
    • Throws: IOException
    • Deprecated because it does not properly convert bytes to characters.
13. long readLong()
    • Reads eight bytes and returns a long.
    • Throws: IOException, EOFException
14. short readShort()
    • Reads two bytes and returns a short.
    • Throws: IOException, EOFException
15. int readUnsignedByte()
    • Reads one byte and returns it as an int in the range [0, 255].
    • Throws: IOException, EOFException
16. int readUnsignedShort()
    • Reads two bytes and returns an int in the range [0, 65535].
    • Throws: IOException, EOFException
17. String readUTF()
    • Reads a string encoded in UTF-8.
    • Returns: The UTF-8 decoded String.
    • Throws: IOException, EOFException

These methods allow efficient reading of structured binary data from an input stream.

Method Signatures found in the DataInputStream class in Java SE 17 .
Review of Method Signatures

Method	Remarks
public final int readUnsignedByte() throws IOException	Defined in DataInputStream, returns an unsigned byte as an int (0-255).
public final short readShort() throws IOException	Reads two bytes as a short.
public final int readUnsignedShort() throws IOException	Reads two bytes as an unsigned short, returning an int (0-65535).
public final char readChar() throws IOException	Reads two bytes as a char.
public final int readInt() throws IOException	Reads four bytes as an int.
public final long readLong() throws IOException	Reads eight bytes as a long.
public final float readFloat() throws IOException	Reads four bytes as a float.
public final double readDouble() throws IOException	Reads eight bytes as a double.
public final String readUTF() throws IOException	Reads a UTF-8 encoded string.
public static final String readUTF(DataInput in) throws IOException	A static method in DataInputStream, used to read a UTF-8 string from a DataInput object.

Final Notes

• The last method (readUTF(DataInput in)) is a static utility method in DataInputStream that allows reading a UTF-8 string from any DataInput instance.
• The final keyword ensures that these methods cannot be overridden in subclasses.

You will notice that every write method in the DataOutputStream class is matched by exactly one corresponding read method in the DataInputStream class. For writeByte(), there is readByte(). For writeShort(), there is readShort(); and so on.
The reverse is not true. The DataInputStream class also has several methods to read data commonly written by non-Java programs such as readUnsignedByte() and readUnsignedShort().

The DataInputStream class has a readLine() method that was used quite commonly in Java 1.0. However it is deprecated in favor of BufferedReader in Java 1.1.

public final String readLine() throws IOException

The DataInputStream class also has useful readFully() methods that read repeatedly from the underlying stream until the byte array is filled. This contrasts with the regular read() methods, which only read as many bytes as are available at the moment.

Click the Exercise link below to write a program that reads a file of floating point radii and writes a file of floating point circumferences.
Portable Formats - Exercise