Related
I know that:
Parsing is the process of turning some kind of data into another kind
of data.
But then I also came across this difference between Scanner and BufferedReader:
BufferedReader is faster than Scanner because BufferedReader does not
need to parse the data.
So my question is how is using Scanner slower than using BufferedReader if I am reading just text file (plain characters) and I am not doing any parsing? Is there any parsing I am not aware of?
Or from following code perspective, how is here Scanner slower because of parsing than using BufferedReader?
//1
BufferedReader bufferedReader = new BufferedReader(new FileReader("xanadu.txt"));
System.out.println(bufferedReader.readLine());
//2
Scanner scanner = new Scanner(new FileReader("xanadu.txt"));
scanner.useDelimiter("\n");
System.out.println(scanner.next());
I don't understand quote how Scanner is slower because of parsing, when I am technically not parsing any data..
Dividing an input stream into lines is a (very limited) form of parsing, but as you say BufferedReader can also do that. The difference, if there is one, will be that BufferedReader can use a highly-optimised procedure to implement a single use case (divide a stream into lines) while Scanner needs to be able to be considerably more flexible (divide a stream into tokens delimited by an arbitrary string or regular expression). Flexibility almost always comes at a price, although you won't know what that cost is without doing some benchmarking. (And it may be very small, since it is conceivable that Scanner has optimised algorithms for particular special cases which it can recognise.)
In short, "because parsing" is not a very good explanation for why one interface is slower than another one. But the more flexibly and precisely you parse an input, the more time it is expected to take.
As far I know, the two most common methods of reading character-based data from a file in Java is using Scanner or BufferedReader. I also know that the BufferedReader reads files efficiently by using a buffer to avoid physical disk operations.
My questions are:
Does Scanner perform as well as BufferedReader?
Why would you choose Scanner over BufferedReader or vice versa?
Scanner is used for parsing tokens from the contents of the stream while BufferedReader just reads the stream and does not do any special parsing.
In fact you can pass a BufferedReader to a scanner as the source of characters to parse.
In currently latest JDK 18 release/build (b37), the Scanner has a smaller buffer (1024 chars) as opposed to the BufferedReader (8192 chars), but it's more than sufficient.
As to the choice, use the Scanner if you want to parse the file, use the BufferedReader if you want to read the file line by line. Also see the introductory text of their aforelinked API documentations.
Parsing = interpreting the given input as tokens (parts). It's able to give back you specific parts directly as int, string, decimal, etc. See also all those nextXxx() methods in Scanner class.
Reading = dumb streaming. It keeps giving back you all characters, which you in turn have to manually inspect if you'd like to match or compose something useful. But if you don't need to do that anyway, then reading is sufficient.
See this link, following is quoted from there:
A BufferedReader is a simple class meant to efficiently read from the
underling stream. Generally, each read request made of a Reader like a
FileReader causes a corresponding read request to be made to
underlying stream. Each invocation of read() or readLine() could
cause bytes to be read from the file, converted into characters, and
then returned, which can be very inefficient. Efficiency is improved
appreciably if a Reader is warped in a BufferedReader.
BufferedReader is synchronized, so read operations on a BufferedReader
can safely be done from multiple threads.
A scanner on the other hand has a lot more cheese built into it; it
can do all that a BufferedReader can do and at the same level of
efficiency as well. However, in addition a Scanner can parse the
underlying stream for primitive types and strings using regular
expressions. It can also tokenize the underlying stream with the
delimiter of your choice. It can also do forward scanning of the
underlying stream disregarding the delimiter!
A scanner however is not thread safe, it has to be externally
synchronized.
The choice of using a BufferedReader or a Scanner depends on the code
you are writing, if you are writing a simple log reader Buffered
reader is adequate. However if you are writing an XML parser Scanner
is the more natural choice.
Even while reading the input, if want to accept user input line by
line and say just add it to a file, a BufferedReader is good enough.
On the other hand if you want to accept user input as a command with
multiple options, and then intend to perform different operations
based on the command and options specified, a Scanner will suit
better.
BufferedReader has significantly larger buffer memory than Scanner. Use BufferedReader if you want to get long strings from a stream, and use Scanner if you want to parse specific type of token from a stream.
Scanner can use tokenize using custom delimiter and parse the stream into primitive types of data, while BufferedReader can only read and store String.
BufferedReader is synchronous while Scanner is not. Use BufferedReader if you're working with multiple threads.
Scanner hides IOException while BufferedReader throws it immediately.
I suggest to use BufferedReader for reading text. Scanner hides IOException while BufferedReader throws it immediately.
The difference between BufferedReader and Scanner are following:
BufferedReader is synchronized but Scanner is not synchronized.
BufferedReader is thread-safe but Scanner is not thread-safe.
BufferedReader has larger buffer memory but Scanner has smaller buffer memory.
BufferedReader is faster but Scanner is slower in execution.
Code to read a line from the console:
BufferedReader:
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
String st = br.readLine();
// You can make the object InputStreamReader object inside the BufferReader method.
BufferReader br = new BufferedReader(InputStreamReader(System.in));
String st = br.readLine();
// You can even inspect the type of the input stream manually by using Parse method which accepts string parameter.
int x = Integer.parseInt(br.readLine());
// Or you can pass the object directly.
int x = Integer.parseInt(st);
Scanner:
Scanner sc = new Scanner(System.in);
String st = sc.nextLine();
The differences between BufferedReader and Scanner are:
BufferedReader reads data, but Scanner parses data.
You can only read String using BufferedReader, using Scanner you can read to different data types like int.
BufferedReader is older than Scanner, it was added on JDK 1.1, while Scanner was added on JDK 5 release.
The buffer size of BufferedReader is larger (8KB) as compared to Scanner's 1KB.
BufferedReader is more suitable for reading files with long String, while Scanner is more suitable for reading small user input from command prompt.
BufferedReader is synchronized, while Scanner is not, which means you cannot share Scanner among multiple threads.
BufferedReader is faster than Scanner because it doesn't spend time on parsing.
BufferedReader is a bit faster as compared to Scanner.
BufferedReader is from java.io package, while Scanner is from java.util package.
On basis of the points we can select our choice.
Thanks for reading!
The Main Differences:
Scanner
Simple text scanner which can parse primitive types and strings using regular expressions.
Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.
Example:
String input = "1 fish 2 fish red fish blue fish";
Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*");
System.out.println(s.nextInt());
System.out.println(s.nextInt());
System.out.println(s.next());
System.out.println(s.next());
s.close();
prints the following output:
1
2
red
blue
The same output can be generated with this code, which uses a regular expression to parse all four tokens at once:
String input = "1 fish 2 fish red fish blue fish";
Scanner s = new Scanner(input);
s.findInLine("(\\d+) fish (\\d+) fish (\\w+) fish (\\w+)");
MatchResult result = s.match();
for (int i = 1; i <= result.groupCount(); i++) {
System.out.println(result.group(i));
}
s.close();
BufferedReader:
Reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.
The buffer size may be specified, or the default size may be used. The default is large enough for most purposes.
In general, each read request made of a Reader causes a corresponding read request to be made of the underlying character or byte stream. It is therefore advisable to wrap a BufferedReader around any Reader whose read() operations may be costly, such as FileReaders and InputStreamReaders. For example,
BufferedReader in = new BufferedReader(new FileReader("foo.in"));
will buffer the input from the specified file. Without buffering, each invocation of read() or readLine() could cause bytes to be read from the file, converted into characters, and then returned, which can be very inefficient.
Programs that use DataInputStreams for textual input can be localized by replacing each DataInputStream with an appropriate BufferedReader.
Source used: https://docs.oracle.com
There are different ways of taking input in java like:
1) BufferedReader 2) Scanner 3) Command Line Arguments
BufferedReader Read text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.
Where Scanner is a simple text scanner which can parse primitive types and strings using regular expressions.
if you are writing a simple log reader Buffered reader is adequate. if you are writing an XML parser Scanner is the more natural choice.
For more information please refer:
http://java.meritcampus.com/t/240/Bufferedreader?tc=mm69
The answer below is taken from Reading from Console: JAVA Scanner vs BufferedReader
When read an input from console, there are two options exists to achieve that. First using Scanner, another using BufferedReader. Both of them have different characteristics. It means differences how to use it.
Scanner treated given input as token. BufferedReader just read line by line given input as string. Scanner itself provides parsing capabilities just like nextInt(), nextFloat().
But, what is others differences between?
Scanner treated given input as token. BufferedReader as stream line/String.
Scanner tokenized given input using regex. Using BufferedReader must write extra code.
BufferedReader faster than Scanner *point no. 2
Scanner isn’t synchronized, BufferedReader synchronized
Scanner came with since JDK 1.5 and higher.
When should use Scanner, or Buffered Reader?
Look at the main differences between both of them, one using tokenized, others using stream line. When you need parsing capabilities, use Scanner instead. But, I am more comfortable with BufferedReader. When you need to read data from a File, use BufferedReader, because it uses buffer memory when it reads a file, and that reduces physical drive usage. Or you can use BufferedReader as input to Scanner.
I prefer Scanner because it doesn't throw checked exceptions and therefore it's usage results in a more streamlined code.
BufferedReader will probably give you better performance (because Scanner is based on InputStreamReader, look sources). oops, for reading data from files it uses nio. When I tested nio performance against BufferedReader performance for big files nio shows a bit better performance.
For reading data from a file try Apache Commons IO.
I have a FileInputStream. I'd like to read character-oriented, linewise data from it, until I find a particular delimiter. Then I'd like to pass the FileInputStream, with the current position set immediately after the end of the delimiter line, to a library that needs an InputStream.
I can use a BufferedReader to walk through the file a line at a time, and everything works great. However, this leaves the underlying file stream in
BufferedReader br = new BufferedReader(new InputStreamReader(myFileStream))
at a non-deterministic position -- the BufferedReader had to look ahead, and I don't know how far, and AFAICT there's no way to tell the BufferedReader to rewind the underlying stream to just after the last-returned line.
Is this the best solution? It seems crazy to have a ReaderInputStream(BufferedReader(InputStreamReader(FileInputStream))) but it's the only way I've seen to avoid rolling my own. I'd really like to avoid writing my own entire stream-that-reads-lines implementation if at all possible.
You cannot unbuffer a buffered reader. You have to use the same wrapper for the life for the application. In your situation I would use
DataInputStream dis = new DataInputStream(new BufferedInputStream(new FileInputStream(file)));
String line = dis.readLine();
While DataInputStream.readLine() is deprecated, it could work for you if you are careful. Otherwise you only option is to read the bytes yourself and parse the text using the encoding required.
I can't seem to determine any difference between InputStreamReader and FileReader besides the way the two are initialized. Is there any benefit to using one or the other? Most other articles cover FileInputStream vs InputStreamReader, but I am contrasting with FileReader instead. Seems to me they both have the same purpose.
First, InputStreamReader can handle all input streams, not just files. Other examples are network connections, classpath resources and ZIP files.
Second, FileReader until Java 11 did not allow you to specify an encoding and instead only used the plaform default encoding, which made it pretty much useless as using it would result in corrupted data when the code is run on systems with different platform default encodings.
Since Java 11, FileReader is a useful shortcut for wrapping an InputStreamReader around a FileInputStream.
FileReader reads character from a file in the file system. InputStreamReader reads characters from any kind of input stream. The stream could be a FileInputStream, but could also be a stream obtained from a socket, an HTTP connection, a database blob, whatever.
I usually prefer using an InputStreamReader wrapping a FileInputStream to read from a file because it allows specifying a specific character encoding.
FileReader extends InputStreamReader. The only differences is that FileReader has constructors which assume you are reading from a file such as String filename, File file and FileDescriptor fd
I suggest you have a look at the source for FileReader to know more.
As far I know, the two most common methods of reading character-based data from a file in Java is using Scanner or BufferedReader. I also know that the BufferedReader reads files efficiently by using a buffer to avoid physical disk operations.
My questions are:
Does Scanner perform as well as BufferedReader?
Why would you choose Scanner over BufferedReader or vice versa?
Scanner is used for parsing tokens from the contents of the stream while BufferedReader just reads the stream and does not do any special parsing.
In fact you can pass a BufferedReader to a scanner as the source of characters to parse.
In currently latest JDK 18 release/build (b37), the Scanner has a smaller buffer (1024 chars) as opposed to the BufferedReader (8192 chars), but it's more than sufficient.
As to the choice, use the Scanner if you want to parse the file, use the BufferedReader if you want to read the file line by line. Also see the introductory text of their aforelinked API documentations.
Parsing = interpreting the given input as tokens (parts). It's able to give back you specific parts directly as int, string, decimal, etc. See also all those nextXxx() methods in Scanner class.
Reading = dumb streaming. It keeps giving back you all characters, which you in turn have to manually inspect if you'd like to match or compose something useful. But if you don't need to do that anyway, then reading is sufficient.
See this link, following is quoted from there:
A BufferedReader is a simple class meant to efficiently read from the
underling stream. Generally, each read request made of a Reader like a
FileReader causes a corresponding read request to be made to
underlying stream. Each invocation of read() or readLine() could
cause bytes to be read from the file, converted into characters, and
then returned, which can be very inefficient. Efficiency is improved
appreciably if a Reader is warped in a BufferedReader.
BufferedReader is synchronized, so read operations on a BufferedReader
can safely be done from multiple threads.
A scanner on the other hand has a lot more cheese built into it; it
can do all that a BufferedReader can do and at the same level of
efficiency as well. However, in addition a Scanner can parse the
underlying stream for primitive types and strings using regular
expressions. It can also tokenize the underlying stream with the
delimiter of your choice. It can also do forward scanning of the
underlying stream disregarding the delimiter!
A scanner however is not thread safe, it has to be externally
synchronized.
The choice of using a BufferedReader or a Scanner depends on the code
you are writing, if you are writing a simple log reader Buffered
reader is adequate. However if you are writing an XML parser Scanner
is the more natural choice.
Even while reading the input, if want to accept user input line by
line and say just add it to a file, a BufferedReader is good enough.
On the other hand if you want to accept user input as a command with
multiple options, and then intend to perform different operations
based on the command and options specified, a Scanner will suit
better.
BufferedReader has significantly larger buffer memory than Scanner. Use BufferedReader if you want to get long strings from a stream, and use Scanner if you want to parse specific type of token from a stream.
Scanner can use tokenize using custom delimiter and parse the stream into primitive types of data, while BufferedReader can only read and store String.
BufferedReader is synchronous while Scanner is not. Use BufferedReader if you're working with multiple threads.
Scanner hides IOException while BufferedReader throws it immediately.
I suggest to use BufferedReader for reading text. Scanner hides IOException while BufferedReader throws it immediately.
The difference between BufferedReader and Scanner are following:
BufferedReader is synchronized but Scanner is not synchronized.
BufferedReader is thread-safe but Scanner is not thread-safe.
BufferedReader has larger buffer memory but Scanner has smaller buffer memory.
BufferedReader is faster but Scanner is slower in execution.
Code to read a line from the console:
BufferedReader:
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
String st = br.readLine();
// You can make the object InputStreamReader object inside the BufferReader method.
BufferReader br = new BufferedReader(InputStreamReader(System.in));
String st = br.readLine();
// You can even inspect the type of the input stream manually by using Parse method which accepts string parameter.
int x = Integer.parseInt(br.readLine());
// Or you can pass the object directly.
int x = Integer.parseInt(st);
Scanner:
Scanner sc = new Scanner(System.in);
String st = sc.nextLine();
The differences between BufferedReader and Scanner are:
BufferedReader reads data, but Scanner parses data.
You can only read String using BufferedReader, using Scanner you can read to different data types like int.
BufferedReader is older than Scanner, it was added on JDK 1.1, while Scanner was added on JDK 5 release.
The buffer size of BufferedReader is larger (8KB) as compared to Scanner's 1KB.
BufferedReader is more suitable for reading files with long String, while Scanner is more suitable for reading small user input from command prompt.
BufferedReader is synchronized, while Scanner is not, which means you cannot share Scanner among multiple threads.
BufferedReader is faster than Scanner because it doesn't spend time on parsing.
BufferedReader is a bit faster as compared to Scanner.
BufferedReader is from java.io package, while Scanner is from java.util package.
On basis of the points we can select our choice.
Thanks for reading!
The Main Differences:
Scanner
Simple text scanner which can parse primitive types and strings using regular expressions.
Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.
Example:
String input = "1 fish 2 fish red fish blue fish";
Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*");
System.out.println(s.nextInt());
System.out.println(s.nextInt());
System.out.println(s.next());
System.out.println(s.next());
s.close();
prints the following output:
1
2
red
blue
The same output can be generated with this code, which uses a regular expression to parse all four tokens at once:
String input = "1 fish 2 fish red fish blue fish";
Scanner s = new Scanner(input);
s.findInLine("(\\d+) fish (\\d+) fish (\\w+) fish (\\w+)");
MatchResult result = s.match();
for (int i = 1; i <= result.groupCount(); i++) {
System.out.println(result.group(i));
}
s.close();
BufferedReader:
Reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.
The buffer size may be specified, or the default size may be used. The default is large enough for most purposes.
In general, each read request made of a Reader causes a corresponding read request to be made of the underlying character or byte stream. It is therefore advisable to wrap a BufferedReader around any Reader whose read() operations may be costly, such as FileReaders and InputStreamReaders. For example,
BufferedReader in = new BufferedReader(new FileReader("foo.in"));
will buffer the input from the specified file. Without buffering, each invocation of read() or readLine() could cause bytes to be read from the file, converted into characters, and then returned, which can be very inefficient.
Programs that use DataInputStreams for textual input can be localized by replacing each DataInputStream with an appropriate BufferedReader.
Source used: https://docs.oracle.com
There are different ways of taking input in java like:
1) BufferedReader 2) Scanner 3) Command Line Arguments
BufferedReader Read text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.
Where Scanner is a simple text scanner which can parse primitive types and strings using regular expressions.
if you are writing a simple log reader Buffered reader is adequate. if you are writing an XML parser Scanner is the more natural choice.
For more information please refer:
http://java.meritcampus.com/t/240/Bufferedreader?tc=mm69
The answer below is taken from Reading from Console: JAVA Scanner vs BufferedReader
When read an input from console, there are two options exists to achieve that. First using Scanner, another using BufferedReader. Both of them have different characteristics. It means differences how to use it.
Scanner treated given input as token. BufferedReader just read line by line given input as string. Scanner itself provides parsing capabilities just like nextInt(), nextFloat().
But, what is others differences between?
Scanner treated given input as token. BufferedReader as stream line/String.
Scanner tokenized given input using regex. Using BufferedReader must write extra code.
BufferedReader faster than Scanner *point no. 2
Scanner isn’t synchronized, BufferedReader synchronized
Scanner came with since JDK 1.5 and higher.
When should use Scanner, or Buffered Reader?
Look at the main differences between both of them, one using tokenized, others using stream line. When you need parsing capabilities, use Scanner instead. But, I am more comfortable with BufferedReader. When you need to read data from a File, use BufferedReader, because it uses buffer memory when it reads a file, and that reduces physical drive usage. Or you can use BufferedReader as input to Scanner.
I prefer Scanner because it doesn't throw checked exceptions and therefore it's usage results in a more streamlined code.
BufferedReader will probably give you better performance (because Scanner is based on InputStreamReader, look sources). oops, for reading data from files it uses nio. When I tested nio performance against BufferedReader performance for big files nio shows a bit better performance.
For reading data from a file try Apache Commons IO.