Reader read(char[], int, int) in Java

read(char[], int, int): This method is available in the java.io.Reader class of Java.

Syntax:

int java.io.Reader.read(char[] cbuf, int off, int len) throws IOException

This method takes three arguments. This method reads characters into a portion of an array.

This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.

Parameters: Three parameters are required for this method.

cbuf: Destination buffer.

off: Offset at which to start storing characters.

len: Maximum number of characters to read.

Returns: The number of characters reads, or -1 if the end of the stream has been reached.

Throws:

1. IOException - If an I/O error occurs.

2. IndexOutOfBoundsException - If off is negative, or len is negative, or len is greater than cbuf.length - off

Approach 1: When no exception

Java

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

public class Readerread4 {
    public static void main(String[] args) throws IOException {

        Reader reader = new StringReader("HELLO");

        char cbuf[] = { 'a', 'b', 'c', 'd', 'e' };
        int off = 0, len = 3;

        System.out.println(reader.read(cbuf, off, len));
        reader.close();

    }
}

Output:

3

Approach 2: IOException 

Java

package com.Reader;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

public class Readerread4 {
    public static void main(String[] args) throws IOException {

        Reader reader = new StringReader("HELLO");

        char cbuf[] = { 'a', 'b', 'c', 'd', 'e' };
        int off = 0, len = 3;

        reader.close();
        System.out.println(reader.read(cbuf, off, len));

    }
}

Output:

Exception in thread "main" java.io.IOException: Stream closed
	at java.base/java.io.StringReader.ensureOpen(StringReader.java:56)
	at java.base/java.io.StringReader.read(StringReader.java:91)
	at com.Reader.Readerread4.main(Readerread4.java:16)

Approach 3: IndexOutOfBoundsException

Java

package com.Reader;

import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;

public class Readerread4 {
    public static void main(String[] args) throws IOException {

        Reader reader = new StringReader("HELLO");

        char cbuf[] = { 'a', 'b', 'c', 'd', 'e' };
        int off = 0, len = 13;

        System.out.println(reader.read(cbuf, off, len));
        reader.close();

    }
}

Output:

Exception in thread "main" java.lang.IndexOutOfBoundsException
	at java.base/java.io.StringReader.read(StringReader.java:94)
	at com.Reader.Readerread4.main(Readerread4.java:15)

Some other methods of Reader

close(): This method closes the stream and releases any system resources associated with it.

mark(int): This method marks the present position in the stream.

markSupported(): This method tells whether this stream supports the mark() operation. 

Reader.nullReader(): This method returns a new Reader that reads no characters.

read(): This method reads a single character.

read(char[]): This method reads characters into an array.

read(CharBuffer): This method attempts to read characters into the specified character buffer.

read(char[], int, int): This method reads characters into a portion of an array.

ready(): This method tells whether this stream is ready to be read.

reset(): This method resets the stream.

skip(long): This method skips characters.

transferTo(Writer): This method reads all characters from this reader and writes the characters to the given writer in the order that they are read.