lispinput.java

计算机代数系统

package net.sf.yacas;


/** \class LispInput : pure abstract class declaring the interface
 *  that needs to be implemented by a file (something that expressions
 *  can be read from).
 */
abstract class LispInput 
{
    /** Constructor with InputStatus. InputStatus retains the information
     * needed when an error occurred, and the file has already been
     * closed.
     */
    public LispInput(InputStatus aStatus)
	{ 
	  iStatus = aStatus;
	}

    /// Return the next character in the file
    public abstract char Next() throws Exception;

    /** Peek at the next character in the file, without advancing the file
     *  pointer.
     */
    public abstract char Peek() throws Exception;

    public InputStatus Status()
	{
	  return iStatus;
	}

    /// Check if the file position is past the end of the file.
    public abstract boolean EndOfStream();
    /** StartPtr returns the start of a buffer, if there is one.
     * Implementations of this class can keep the file in memory
     * as a whole, and return the start pointer and current position.
     * Especially the parsing code requires this, because it can then
     * efficiently look up a symbol in the hash table without having to
     * first create a buffer to hold the symbol in. If StartPtr is supported,
     * the whole file should be in memory for the whole period the file
     * is being read.
     */
    public abstract StringBuffer StartPtr();
    public abstract int Position();
    public abstract void SetPosition(int aPosition);

    InputStatus iStatus;
};