Permutation

Permutation.java

import java.util.ArrayList;

public interface Permutation extends Iterable<Integer>{

	// Build a new Permutation by composition of this and other
	public Permutation compose(Permutation other);
	
	// Get element of Permutation at index
	public Integer sigma(Integer index);
	
	// Get number of elements
	public Integer getSize();
	
	// Get list of elements
	public ArrayList<Integer> getElements();
}

PermutationImpl.java

import java.util.ArrayList;
import java.util.Iterator;

public class PermutationImpl implements Permutation {
	
	public PermutationImpl(ArrayList<Integer> resultList) {
		// TODO Auto-generated constructor stub
	}

	/* (non-Javadoc)
	 * @see Permutation#compose(Permutation)
	 */
	@Override
	public Permutation compose(Permutation other) {
		// Checks:
		// Same cardinality
		// Same range (1...n)
		// -> Both are Permutation objects, should be valid
		
		// Example:
		// [2,4,5,1,3] this
		// [3,5,1,4,2] other
		// [5,4,2,3,1] composite
		
		ArrayList<Integer> resultList = new ArrayList<Integer>();
		for(Integer element: this) {
			resultList.add(other.sigma(element));
		}
		Permutation result = new PermutationImpl(resultList);
		return result;
	}
	
	public int hashCode() {
		// Delegate HashCode to element list
		return getElements().hashCode();
	}
	
	public boolean equals(Object other) {
		boolean result = false;
		
		// Reference Test
		if (this == other) {
			result = true;
		}
		// Type test (instanceof)
		else if (other instanceof Permutation) {
			// Attribute test
			if (this.getSize() == ((Permutation)other).getSize()
				&& this.getElements().equals(((Permutation)other).getElements())) {
				result = true;
			}
		}
		return result;
	}

	@Override
	public Iterator<Integer> iterator() {
		return getElements().iterator();
	}
	
	@Override
	public Integer getSize() {
		return getElements().size();
	}

	@Override
	public Integer sigma(Integer index) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public ArrayList<Integer> getElements() {
		// TODO Auto-generated method stub
		return null;
	}
}