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Library providing immutable/persistent collection classes for Java. While collections are immutable they provide methods for adding and removing values by creating new modified copies of themselves. Each copy shares almost all of its structure with other copies to minimize memory consumption.

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// Burton Computer Corporation
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package org.javimmutable.collections;

/**
 * Implemented by objects used to traverse persistent data structures.
 * The iterators themselves must be immutable and always create a new
 * iterator when next() is called.
 *
 * @param 
 */
public interface Cursor
{
    /**
     * Advances to the next (possibly first) value.  Must always return a non-null Cursor.
     * A newly created Cursor must always point to "before" the first value because next() will always
     * be called once before retrieving the first value.  If the Cursor is already at the end
     * of its sequence then it should return a Cursor that will always return false for hasValue().
     *
     * @return iterator for next position
     */
    Cursor next();

    /**
     * Read-only method with no side effects that determines if the Cursor currently has a value.
     * Users of the Cursor will always call this after calling next() to see if they have reached
     * the end of the sequence.  If hasValue() returns true then next() will be called.  If hasValue()
     * returns false then next() must not be called.
     *
     * @return true iff getValue() can be called
     */
    boolean hasValue();

    /**
     * Return the value at the Cursor's position.  Only valid if a call to hasValue() would return true.
     *
     * @return current value
     * @throws IllegalStateException if getValue() is not allowed for this iterator
     */
    V getValue();
}