BufferedReader default buffer size?

Question

According to the documentation, BufferedReader(Reader) uses a default buffer size, while the second constructor, BufferedReader(Reader, int) allows the buffer size to be set.

public BufferedReader(Reader in)

Creates a buffering character-input stream that uses a default-sized input buffer.

However, the docs do not not mention what the default buffer size is.

What is the default buffer size of a BufferedReader?

@Vulcan EJP gave you a wrong answer then. as said I've extraced the actual .jar containing BufferedReader and took a look at it. maybe it was other way for some years, or will be other way in future, but now it is stricctly specified to 8192 in the java.io.BufferedReader!!! — IAM
– IAM, Commented Jun 7, 2013 at 8:10
@Vulcan android was jsut an example of documentation. actual proof followed later. but since android also uses rt.jar, transitively the documentation is enough. — IAM
– IAM, Commented Jun 7, 2013 at 8:12
@IAM I did not give a wrong answer. I stated that it (a) is unspecified and (b) had been 4096 in the Oracle/Sun code for many years. They are free to change it at any time because it is unspecified. — user207421
– user207421, Commented Sep 24, 2016 at 10:47

IAM · Accepted Answer · 2013-06-07 02:15:27Z

11

The default buffer size is 8192 characters

http://developer.android.com/reference/java/io/BufferedReader.html

 BufferedReader(Reader in)
Constructs a new BufferedReader, providing in with a buffer of 8192 characters.

Besides this documentation, I've extraced the rt.jar archive, and decompiled the BufferedReader.class from java.io.* using JD-GUI, this is what I found in the class definition:

private static int defaultCharBufferSize = 8192;

edited Jun 7, 2013 at 2:15

answered Jun 6, 2013 at 23:26

IAM

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9 Comments

7stud Over a year ago

You may be right, but the official docs don't say that: docs.oracle.com/javase/7/docs/api

Smit Over a year ago

@7stud Take a look at link given in my comment.

7stud Over a year ago

@Smit, Back at ya: take a look at the oracle link in my comment.

Smit Over a year ago

@7stud I already looked at Javadoc API, and so my search ended me at that link. Anyhow lots of other forums says the same size and I ran your program and gave me 8192

FThompson Over a year ago

While the official docs do not mention this, I just took a look through the source code, and it is indeed 8192. Thanks.

|

user207421 · Accepted Answer · 2013-06-07 02:20:21Z

2

It isn't specified. On purpose. It's been 4096 for some years in the Sun/Oracle Java JDKs but don't rely on it.

answered Jun 7, 2013 at 2:20

user207421

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2 Comments

pevik Over a year ago

It might be platform dependent, but it's 8192 on current Android.

user207421 Over a year ago

@Pevik Your link is to BufferedInputStream, and the question is about BufferedReader.

Community · Accepted Answer · 2017-05-23 10:34:08Z

1

~~I'm sure~~ I think it may be system/jvm dependent. Run this program:

What are the default buffer size for java.io.BufferedInputStream on old and exotic JVMs?

import java.io.BufferedInputStream;
import java.io.InputStream;

public class BufferSizeDetector extends BufferedInputStream {
    public static void main(String[] args) {
        BufferSizeDetector bsd = new BufferSizeDetector(null);

        System.err.println(System.getProperty("java.version"));
        System.err.println(bsd.getBufferSize());
    }

    public BufferSizeDetector(InputStream in) {
        super(in);
    }

    public int getBufferSize() {
        return super.buf.length;
    }
}

I get:

1.6.0_45
8192

edited May 23, 2017 at 10:34

CommunityBot

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answered Jun 6, 2013 at 23:29

7stud

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2 Comments

FThompson Over a year ago

Interesting, but what assures that BufferedReader and BufferedInputStream have the same default buffer size?

7stud Over a year ago

@Vulcan, Good point. (Stupid BufferedReader class doesn't have a buf field).

Suraj Rao · Accepted Answer · 2019-03-18 12:23:38Z

1

Ans is 8 KB.

1024 bytes * 8 = 8192 (8 KB)
refer class : java.io.BufferedReader

private static int defaultCharBufferSize = 8192;

edited Mar 18, 2019 at 12:23

Suraj Rao

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answered Mar 18, 2019 at 12:17

GovindaRaju

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