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

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

Syntax:

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

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

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 read, 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

3. NullPointerException: if cbuf is null.

Approach 1: When no exception

Java

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

public class FilterReaderread2 {
    public static void main(String[] args) throws IOException {

        Reader reader = new StringReader("hello");
        FilterReader filterReader = new FilterReader(reader) {
        };

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

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

Output:

3

Approach 2: IOException

Java

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

public class FilterReaderread2 {
    public static void main(String[] args) throws IOException {

        Reader reader = new StringReader("hello");
        FilterReader filterReader = new FilterReader(reader) {
        };

        char cbuf[] = { 'a', 'c', 'd', 'e', 'r' };
        int off = 0, len = 3;
        filterReader.close();
        System.out.println(filterReader.read(cbuf, off, len));
        filterReader.close();
    }
}

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 java.base/java.io.FilterReader.read(FilterReader.java:75)
	

Approach 3: IndexOutOfBoundsException 

Java

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

public class FilterReaderread2 {
    public static void main(String[] args) throws IOException {

        Reader reader = new StringReader("hello");
        FilterReader filterReader = new FilterReader(reader) {
        };

        char cbuf[] = { 'a', 'c', 'd', 'e', 'r' };
        int off = 0, len = 100;
        System.out.println(filterReader.read(cbuf, off, len));
        filterReader.close();
    }
}

Output:

Exception in thread "main" java.lang.IndexOutOfBoundsException
	at java.base/java.io.StringReader.read(StringReader.java:94)
	at java.base/java.io.FilterReader.read(FilterReader.java:75)
	

Approach 4: NullPointerException

Java

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

public class FilterReaderread2 {
    public static void main(String[] args) throws IOException {

        Reader reader = new StringReader("hello");
        FilterReader filterReader = new FilterReader(reader) {
        };

        char cbuf[] = null;
        int off = 0, len = 3;

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

Output:

Exception in thread "main" java.lang.NullPointerException: Cannot read the array length because "cbuf" is null
	at java.base/java.io.StringReader.read(StringReader.java:92)
	at java.base/java.io.FilterReader.read(FilterReader.java:75)
	

Some more methods of FilterReader class.

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.

read(): This method reads a single character.

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

reset(): This method resets the stream.

skip(long): This method skips characters.