Tuple.java

package simpledb;

import java.io.Serializable;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Tuple maintains information about the contents of a tuple. Tuples have a
 * specified schema specified by a TupleDesc object and contain Field objects
 * with the data for each field.
 */
public class Tuple implements Serializable {

    private static final long serialVersionUID = 1L;

    private TupleDesc td;
    private Field[] fields;
    private RecordId rid;
    
    /**
     * Create a new tuple with the specified schema (type).
     * 
     * @param td
     *            the schema of this tuple. It must be a valid TupleDesc
     *            instance with at least one field.
     */
    public Tuple(TupleDesc td) {
        // Done
    	this.td = td;
    	fields = new Field[td.numFields()];
    }

    /**
     * @return The TupleDesc representing the schema of this tuple.
     */
    public TupleDesc getTupleDesc() {
        // Done
        return td;
    }

    /**
     * @return The RecordId representing the location of this tuple on disk. May
     *         be null.
     */
    public RecordId getRecordId() {
        // Done
        return rid;
    }

    /**
     * Set the RecordId information for this tuple.
     * 
     * @param rid
     *            the new RecordId for this tuple.
     */
    public void setRecordId(RecordId rid) {
        // Done
    	this.rid = rid;
    }

    /**
     * Change the value of the ith field of this tuple.
     * 
     * @param i
     *            index of the field to change. It must be a valid index.
     * @param f
     *            new value for the field.
     */
    public void setField(int i, Field f) {
        // Done
    	fields[i] = f;
    }

    /**
     * @return the value of the ith field, or null if it has not been set.
     * 
     * @param i
     *            field index to return. Must be a valid index.
     */
    public Field getField(int i) {
        // Done
        return fields[i];
    }

    /**
     * Returns the contents of this Tuple as a string. Note that to pass the
     * system tests, the format needs to be as follows:
     * 
     * column1\tcolumn2\tcolumn3\t...\tcolumnN\n
     * 
     * where \t is any whitespace, except newline, and \n is a newline
     */
    public String toString() {
    	// Done
    	StringBuilder sb = new StringBuilder();
    	
    	sb.append(fields[0].toString());
    	for  (int i=1; i<fields.length; i++) {
    		sb.append("\t"+fields[i].toString());
    	}
        return sb.toString();
    }
    
    /**
     * @return
     *        An iterator which iterates over all the fields of this tuple
     * */
    public Iterator<Field> fields() {
        // Done
    	return new Iterator<Field>() {
    		private int idx = -1;
    		
			@Override
			public boolean hasNext() {
				return idx+1<fields.length;
			}
			@Override
			public Field next() {
				if (++idx == fields.length) {
					throw new NoSuchElementException();
				} else {
					return fields[idx];
				}
			}
			@Override
			public void remove() {
				
			}
    	};
    }
    
    /**
     * reset the TupleDesc of this tuple
     * */
    public void resetTupleDesc(TupleDesc td) {
        // Done
    	this.td = td;
    }
}