本文详细介绍了Java中DataOutput接口的功能与使用方法，包括如何将各种基本类型的数据转换为字节序列并写入到二进制流中。此外还讲解了字符串转换为Java Modified UTF-8格式的方法。
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Copyright © 2006 Sun Microsystems, Inc. and Motorola, Inc. All rights reserved.
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java.io
Interface DataOutput
All Known Subinterfaces:
Datagram
All Known Implementing Classes:
DataOutputStream
public interface DataOutput
The DataOutput interface provides for converting data from any of the Java primitive types to a series of bytes and writing these bytes to a binary stream. There is also a facility for converting a String into Java modified UTF-8 format and writing the resulting series of bytes.
For all the methods in this interface that write bytes, it is generally true that if a byte cannot be written for any reason, an IOException is thrown.
Since:
JDK1.0, CLDC 1.0
See Also:
DataInput, DataOutputStream
Method Summary
void write(byte[] b)
Writes to the output stream all the bytes in array b.
void write(byte[] b, int off, int len)
Writes len bytes from array b, in order, to the output stream.
void write(int b)
Writes to the output stream the eight low-order bits of the argument b.
void writeBoolean(boolean v)
Writes a boolean value to this output stream.
void writeByte(int v)
Writes to the output stream the eight low- order bits of the argument v.
void writeChar(int v)
Writes a char value, which is comprised of two bytes, to the output stream.
void writeChars(String s)
Writes every character in the string s, to the output stream, in order, two bytes per character.
void writeDouble(double v)
Writes a double value, which is comprised of eight bytes, to the output stream.
void writeFloat(float v)
Writes a float value, which is comprised of four bytes, to the output stream.
void writeInt(int v)
Writes an int value, which is comprised of four bytes, to the output stream.
void writeLong(long v)
Writes an long value, which is comprised of four bytes, to the output stream.
void writeShort(int v)
Writes two bytes to the output stream to represent the value of the argument.
void writeUTF(String s)
Writes two bytes of length information to the output stream, followed by the Java modified UTF representation of every character in the string s.
Method Detail
write
public void write(int b)
throws IOException
Writes to the output stream the eight low-order bits of the argument b. The 24 high-order bits of b are ignored.
Parameters:
b - the byte to be written.
Throws:
IOException - if an I/O error occurs.
write
public void write(byte[] b)
throws IOException
Writes to the output stream all the bytes in array b. If b is null, a NullPointerException is thrown. If b.length is zero, then no bytes are written. Otherwise, the byte b[0] is written first, then b[1], and so on; the last byte written is b[b.length-1].
Parameters:
b - the data.
Throws:
IOException - if an I/O error occurs.
write
public void write(byte[] b,
int off,
int len)
throws IOException
Writes len bytes from array b, in order, to the output stream. If b is null, a NullPointerException is thrown. If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown. If len is zero, then no bytes are written. Otherwise, the byte b[off] is written first, then b[off+1], and so on; the last byte written is b[off+len-1].
Parameters:
b - the data.
off - the start offset in the data.
len - the number of bytes to write.
Throws:
IOException - if an I/O error occurs.
writeBoolean
public void writeBoolean(boolean v)
throws IOException
Writes a boolean value to this output stream. If the argument v is true, the value (byte)1 is written; if v is false, the value (byte)0 is written. The byte written by this method may be read by the readBoolean method of interface DataInput, which will then return a boolean equal to v.
Parameters:
v - the boolean to be written.
Throws:
IOException - if an I/O error occurs.
writeByte
public void writeByte(int v)
throws IOException
Writes to the output stream the eight low- order bits of the argument v. The 24 high-order bits of v are ignored. (This means that writeByte does exactly the same thing as write for an integer argument.) The byte written by this method may be read by the readByte method of interface DataInput, which will then return a byte equal to (byte)v.
Parameters:
v - the byte value to be written.
Throws:
IOException - if an I/O error occurs.
writeShort
public void writeShort(int v)
throws IOException
Writes two bytes to the output stream to represent the value of the argument. The byte values to be written, in the order shown, are:
(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readShort method of interface DataInput, which will then return a short equal to (short)v.
Parameters:
v - the short value to be written.
Throws:
IOException - if an I/O error occurs.
writeChar
public void writeChar(int v)
throws IOException
Writes a char value, which is comprised of two bytes, to the output stream. The byte values to be written, in the order shown, are:
(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readChar method of interface DataInput, which will then return a char equal to (char)v.
Parameters:
v - the char value to be written.
Throws:
IOException - if an I/O error occurs.
writeInt
public void writeInt(int v)
throws IOException
Writes an int value, which is comprised of four bytes, to the output stream. The byte values to be written, in the order shown, are:
(byte)(0xff & (v >> 24))
(byte)(0xff & (v >> 16))
(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readInt method of interface DataInput, which will then return an int equal to v.
Parameters:
v - the int value to be written.
Throws:
IOException - if an I/O error occurs.
writeLong
public void writeLong(long v)
throws IOException
Writes an long value, which is comprised of four bytes, to the output stream. The byte values to be written, in the order shown, are:
(byte)(0xff & (v >> 56))
(byte)(0xff & (v >> 48))
(byte)(0xff & (v >> 40))
(byte)(0xff & (v >> 32))
(byte)(0xff & (v >> 24))
(byte)(0xff & (v >> 16))
(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readLong method of interface DataInput, which will then return a long equal to v.
Parameters:
v - the long value to be written.
Throws:
IOException - if an I/O error occurs.
writeFloat
public void writeFloat(float v)
throws IOException
Writes a float value, which is comprised of four bytes, to the output stream. It does this as if it first converts this float value to an int in exactly the manner of the Float.floatToIntBits method and then writes the int value in exactly the manner of the writeInt method. The bytes written by this method may be read by the readFloat method of interface DataInput, which will then return a float equal to v.
Parameters:
v - the float value to be written.
Throws:
IOException - if an I/O error occurs.
Since:
CLDC 1.1
writeDouble
public void writeDouble(double v)
throws IOException
Writes a double value, which is comprised of eight bytes, to the output stream. It does this as if it first converts this double value to a long in exactly the manner of the Double.doubleToLongBits method and then writes the long value in exactly the manner of the writeLong method. The bytes written by this method may be read by the readDouble method of interface DataInput, which will then return a double equal to v.
Parameters:
v - the double value to be written.
Throws:
IOException - if an I/O error occurs.
Since:
CLDC 1.1
writeChars
public void writeChars(String s)
throws IOException
Writes every character in the string s, to the output stream, in order, two bytes per character. If s is null, a NullPointerException is thrown. If s.length is zero, then no characters are written. Otherwise, the character s[0] is written first, then s[1], and so on; the last character written is s[s.length-1]. For each character, two bytes are actually written, high-order byte first, in exactly the manner of the writeChar method.
Parameters:
s - the string value to be written.
Throws:
IOException - if an I/O error occurs.
writeUTF
public void writeUTF(String s)
throws IOException
Writes two bytes of length information to the output stream, followed by the Java modified UTF representation of every character in the string s. If s is null, a NullPointerException is thrown. Each character in the string s is converted to a group of one, two, or three bytes, depending on the value of the character.
If a character c is in the range \u0001 through \u007f, it is represented by one byte:
(byte)c
If a character c is \u0000 or is in the range \u0080 through \u07ff, then it is represented by two bytes, to be written in the order shown:
(byte)(0xc0 | (0x1f & (c >> 6)))
(byte)(0x80 | (0x3f & c))
If a character c is in the range \u0800 through uffff, then it is represented by three bytes, to be written in the order shown:
(byte)(0xe0 | (0x0f & (c >> 12)))
(byte)(0x80 | (0x3f & (c >> 6)))
(byte)(0x80 | (0x3f & c))
First, the total number of bytes needed to represent all the characters of s is calculated. If this number is larger than 65535, then a UTFDataFormatError is thrown. Otherwise, this length is written to the output stream in exactly the manner of the writeShort method; after this, the one-, two-, or three-byte representation of each character in the string s is written.
The bytes written by this method may be read by the readUTF method of interface DataInput, which will then return a String equal to s.
Parameters:
s - the string value to be written.
Throws:
IOException - if an I/O error occurs.
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Copyright © 2006 Sun Microsystems, Inc. and Motorola, Inc. All rights reserved. Use is subject to License Terms. Your use of this web site or any of its content or software indicates your agreement to be bound by these License Terms.
For more information, please consult the JSR 118 specification.
Copyright © 2006 Sun Microsystems, Inc. and Motorola, Inc. All rights reserved.
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SUMMARY: NESTED | FIELD | CONSTR | METHOD DETAIL: FIELD | CONSTR | METHOD
java.io
Interface DataOutput
All Known Subinterfaces:
Datagram
All Known Implementing Classes:
DataOutputStream
public interface DataOutput
The DataOutput interface provides for converting data from any of the Java primitive types to a series of bytes and writing these bytes to a binary stream. There is also a facility for converting a String into Java modified UTF-8 format and writing the resulting series of bytes.
For all the methods in this interface that write bytes, it is generally true that if a byte cannot be written for any reason, an IOException is thrown.
Since:
JDK1.0, CLDC 1.0
See Also:
DataInput, DataOutputStream
Method Summary
void write(byte[] b)
Writes to the output stream all the bytes in array b.
void write(byte[] b, int off, int len)
Writes len bytes from array b, in order, to the output stream.
void write(int b)
Writes to the output stream the eight low-order bits of the argument b.
void writeBoolean(boolean v)
Writes a boolean value to this output stream.
void writeByte(int v)
Writes to the output stream the eight low- order bits of the argument v.
void writeChar(int v)
Writes a char value, which is comprised of two bytes, to the output stream.
void writeChars(String s)
Writes every character in the string s, to the output stream, in order, two bytes per character.
void writeDouble(double v)
Writes a double value, which is comprised of eight bytes, to the output stream.
void writeFloat(float v)
Writes a float value, which is comprised of four bytes, to the output stream.
void writeInt(int v)
Writes an int value, which is comprised of four bytes, to the output stream.
void writeLong(long v)
Writes an long value, which is comprised of four bytes, to the output stream.
void writeShort(int v)
Writes two bytes to the output stream to represent the value of the argument.
void writeUTF(String s)
Writes two bytes of length information to the output stream, followed by the Java modified UTF representation of every character in the string s.
Method Detail
write
public void write(int b)
throws IOException
Writes to the output stream the eight low-order bits of the argument b. The 24 high-order bits of b are ignored.
Parameters:
b - the byte to be written.
Throws:
IOException - if an I/O error occurs.
write
public void write(byte[] b)
throws IOException
Writes to the output stream all the bytes in array b. If b is null, a NullPointerException is thrown. If b.length is zero, then no bytes are written. Otherwise, the byte b[0] is written first, then b[1], and so on; the last byte written is b[b.length-1].
Parameters:
b - the data.
Throws:
IOException - if an I/O error occurs.
write
public void write(byte[] b,
int off,
int len)
throws IOException
Writes len bytes from array b, in order, to the output stream. If b is null, a NullPointerException is thrown. If off is negative, or len is negative, or off+len is greater than the length of the array b, then an IndexOutOfBoundsException is thrown. If len is zero, then no bytes are written. Otherwise, the byte b[off] is written first, then b[off+1], and so on; the last byte written is b[off+len-1].
Parameters:
b - the data.
off - the start offset in the data.
len - the number of bytes to write.
Throws:
IOException - if an I/O error occurs.
writeBoolean
public void writeBoolean(boolean v)
throws IOException
Writes a boolean value to this output stream. If the argument v is true, the value (byte)1 is written; if v is false, the value (byte)0 is written. The byte written by this method may be read by the readBoolean method of interface DataInput, which will then return a boolean equal to v.
Parameters:
v - the boolean to be written.
Throws:
IOException - if an I/O error occurs.
writeByte
public void writeByte(int v)
throws IOException
Writes to the output stream the eight low- order bits of the argument v. The 24 high-order bits of v are ignored. (This means that writeByte does exactly the same thing as write for an integer argument.) The byte written by this method may be read by the readByte method of interface DataInput, which will then return a byte equal to (byte)v.
Parameters:
v - the byte value to be written.
Throws:
IOException - if an I/O error occurs.
writeShort
public void writeShort(int v)
throws IOException
Writes two bytes to the output stream to represent the value of the argument. The byte values to be written, in the order shown, are:
(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readShort method of interface DataInput, which will then return a short equal to (short)v.
Parameters:
v - the short value to be written.
Throws:
IOException - if an I/O error occurs.
writeChar
public void writeChar(int v)
throws IOException
Writes a char value, which is comprised of two bytes, to the output stream. The byte values to be written, in the order shown, are:
(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readChar method of interface DataInput, which will then return a char equal to (char)v.
Parameters:
v - the char value to be written.
Throws:
IOException - if an I/O error occurs.
writeInt
public void writeInt(int v)
throws IOException
Writes an int value, which is comprised of four bytes, to the output stream. The byte values to be written, in the order shown, are:
(byte)(0xff & (v >> 24))
(byte)(0xff & (v >> 16))
(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readInt method of interface DataInput, which will then return an int equal to v.
Parameters:
v - the int value to be written.
Throws:
IOException - if an I/O error occurs.
writeLong
public void writeLong(long v)
throws IOException
Writes an long value, which is comprised of four bytes, to the output stream. The byte values to be written, in the order shown, are:
(byte)(0xff & (v >> 56))
(byte)(0xff & (v >> 48))
(byte)(0xff & (v >> 40))
(byte)(0xff & (v >> 32))
(byte)(0xff & (v >> 24))
(byte)(0xff & (v >> 16))
(byte)(0xff & (v >> 8))
(byte)(0xff & v)
The bytes written by this method may be read by the readLong method of interface DataInput, which will then return a long equal to v.
Parameters:
v - the long value to be written.
Throws:
IOException - if an I/O error occurs.
writeFloat
public void writeFloat(float v)
throws IOException
Writes a float value, which is comprised of four bytes, to the output stream. It does this as if it first converts this float value to an int in exactly the manner of the Float.floatToIntBits method and then writes the int value in exactly the manner of the writeInt method. The bytes written by this method may be read by the readFloat method of interface DataInput, which will then return a float equal to v.
Parameters:
v - the float value to be written.
Throws:
IOException - if an I/O error occurs.
Since:
CLDC 1.1
writeDouble
public void writeDouble(double v)
throws IOException
Writes a double value, which is comprised of eight bytes, to the output stream. It does this as if it first converts this double value to a long in exactly the manner of the Double.doubleToLongBits method and then writes the long value in exactly the manner of the writeLong method. The bytes written by this method may be read by the readDouble method of interface DataInput, which will then return a double equal to v.
Parameters:
v - the double value to be written.
Throws:
IOException - if an I/O error occurs.
Since:
CLDC 1.1
writeChars
public void writeChars(String s)
throws IOException
Writes every character in the string s, to the output stream, in order, two bytes per character. If s is null, a NullPointerException is thrown. If s.length is zero, then no characters are written. Otherwise, the character s[0] is written first, then s[1], and so on; the last character written is s[s.length-1]. For each character, two bytes are actually written, high-order byte first, in exactly the manner of the writeChar method.
Parameters:
s - the string value to be written.
Throws:
IOException - if an I/O error occurs.
writeUTF
public void writeUTF(String s)
throws IOException
Writes two bytes of length information to the output stream, followed by the Java modified UTF representation of every character in the string s. If s is null, a NullPointerException is thrown. Each character in the string s is converted to a group of one, two, or three bytes, depending on the value of the character.
If a character c is in the range \u0001 through \u007f, it is represented by one byte:
(byte)c
If a character c is \u0000 or is in the range \u0080 through \u07ff, then it is represented by two bytes, to be written in the order shown:
(byte)(0xc0 | (0x1f & (c >> 6)))
(byte)(0x80 | (0x3f & c))
If a character c is in the range \u0800 through uffff, then it is represented by three bytes, to be written in the order shown:
(byte)(0xe0 | (0x0f & (c >> 12)))
(byte)(0x80 | (0x3f & (c >> 6)))
(byte)(0x80 | (0x3f & c))
First, the total number of bytes needed to represent all the characters of s is calculated. If this number is larger than 65535, then a UTFDataFormatError is thrown. Otherwise, this length is written to the output stream in exactly the manner of the writeShort method; after this, the one-, two-, or three-byte representation of each character in the string s is written.
The bytes written by this method may be read by the readUTF method of interface DataInput, which will then return a String equal to s.
Parameters:
s - the string value to be written.
Throws:
IOException - if an I/O error occurs.
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Copyright © 2006 Sun Microsystems, Inc. and Motorola, Inc. All rights reserved. Use is subject to License Terms. Your use of this web site or any of its content or software indicates your agreement to be bound by these License Terms.
For more information, please consult the JSR 118 specification.
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