piycomparator.java

PIY(Program It Yourself)是一个基于Java的应用程序开发环境

package piy;

import java.io.Serializable;

/**
* Represents an abstract comparator - a class that can be used to compare two objects.
* Each comparator can provide any number of comparison methods, for example a String
* comparator might return true if stringA starts with stringB, or stringA ends with
* stringB, etc.  Negative statements need not (should not) be provided - PIY
* gives the user the option to negate.<p>
* Classes extending this should include the code (in the constructor) 
* <code>super.init(this)</code> to initialise the class.
* @author David Vivash
* @version 1.0, 30/04/01
*/
public abstract class PIYComparator extends BooleanComparable implements Serializable {
	private FixedProperty first = null, second = null;
	private String mode = null;

	private PIYComparator implementingClass = null;

	/**
	* Initialises the new PIYComparator. If the extending class does not return
	* an array of strings containing at least one element from the getModes() method,
	* this method throws a PIYComparatorError.
	* @param instance the instance object of the extending PIYComparator class
	*/
	public void init(PIYComparator instance) {
		if (instance == null) throw new PIYComparatorError();
		
		implementingClass = instance;
		
		first	= new FixedProperty(null, instance.getFirstType());
		second	= new FixedProperty(null, instance.getSecondType());

		String[] modes = instance.getModes();
		if ((modes == null) || (modes.length == 0)) throw new PIYComparatorError();
		else mode = modes[0];
	}

	/**
	* Get the first object for comparison
	* @return the first object
	*/
	public FixedProperty getFirst() { return first; }

	
	/**
	* Get the second object for comparison, the thing the first object is being compared to
	* @return the second object
	*/
	public FixedProperty getSecond() { return second; }

	/**
	* Gets what type the first object should be.  The <code>first</code> object will
	* be set up to have this type.  If there is no type, and support should not be set up,
	* this method should be set up to return void.class.
	*/
	public abstract Class getFirstType();

	/**
	* Gets what type the first object should be.  The <code>second</code> object will
	* be set up to have this type. If there is no type, and support should not be set up,
	* this method should be set up to return void.class.
	*/
	public abstract Class getSecondType();

	/**
	* Gets the mode of operation for this comparator.
	* @return the currently selected mode
	*/
	public String getMode() { return mode; }

	/**
	* Set the mode of operation for this comparator.  If the mode is not valid, ie. not one
	* of the modes specified in getModes(), the mode will remain with its previous value. 
	* @param val the mode to set
	*/
	public void setMode(String val) { 
		String[] modes = implementingClass.getModes();

		for (int i=0; i<modes.length; i++)
			if (modes[i] == val) mode = val;

	}

	public abstract String[] getModes();

}


class PIYComparatorError extends Error {
	public PIYComparatorError() { super(); }
}