PowerPoint Presentation - Composite and Interpreter Pattern

Singleton IntList

import java.util.NoSuchElementException;

abstract class IntList {

abstract int getFirst();

abstract IntList getRest();

}

class Empty extends IntList {

static final Empty ONLY = new Empty();

private Empty() {}

int getFirst() {

throw new

NoSuchElementException("getFirst applied to Empty()");

}

int getRest() {

throw new

NoSuchElementException("getRest applied to Empty()");

}

public String toString() { return "Empty()"; }

}

class NonEmpty extends IntList {

int first;

IntList rest;

int getFirst() { return first; );

IntList getRest() { return rest; }

public String toString() { return "NonEmpty(" + first + ", " + rest + ")"; }

}

Static member holding the unique instance

Private constructor