https://openjdk.java.net/ 
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package java.lang;

import java.io.IOException;


A Readable is a source of characters. Characters from a Readable are made available to callers of the read method via a CharBuffer. 
Since:1.5
/**
 * A {@code Readable} is a source of characters. Characters from
 * a {@code Readable} are made available to callers of the read
 * method via a {@link java.nio.CharBuffer CharBuffer}.
 *
 * @since 1.5
 */
public interface Readable {

    
Attempts to read characters into the specified character buffer.
The buffer is used as a repository of characters as-is: the only
changes made are the results of a put operation. No flipping or
rewinding of the buffer is performed.

Params:
  • cb – the buffer to read characters into
Throws:
Returns:The number of char values added to the buffer, or -1 if this source of characters is at its end
/**
     * Attempts to read characters into the specified character buffer.
     * The buffer is used as a repository of characters as-is: the only
     * changes made are the results of a put operation. No flipping or
     * rewinding of the buffer is performed.
     *
     * @param cb the buffer to read characters into
     * @return The number of {@code char} values added to the buffer,
     *                 or -1 if this source of characters is at its end
     * @throws IOException if an I/O error occurs
     * @throws NullPointerException if cb is null
     * @throws java.nio.ReadOnlyBufferException if cb is a read only buffer
     */
    public int read(java.nio.CharBuffer cb) throws IOException;
}