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Thanks, Andrew.

Thanks, Andrew. Reminders: wear the wireless mike combination is 1-31 speak slowly, pause for questions I’d rather you get through less material than try to rush through the slides bring whiteboard markers/eraser make sure writing is LARGE ENOUGH to be seen in back of room use BOLD colors.

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Thanks, Andrew.

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  1. Thanks, Andrew. • Reminders: • wear the wireless mike • combination is 1-31 • speak slowly, pause for questions • I’d rather you get through less material than try to rush through the slides • bring whiteboard markers/eraser • make sure writing is LARGE ENOUGH to be seen in back of room • use BOLD colors

  2. CSE115: Introduction to Computer Science I Dr. Carl Alphonce 343 Davis Hall 645-4739 alphonce@buffalo.edu

  3. Agenda • Announcements • Cell phones / laptops off & away / Name signs out • Last time • Our second relationship: Association • Methods with parameters • Today • null • this (revisited) • interfaces (if time permits)

  4. Announcements • Exam 2 – three weeks away (Wednesday after spring break) • covers material from exam 1 up to & including 3/9 • review on Monday 3/19 • exam on Wednesday 3/21 • No recitations in exam week: 3/19 – 3/23

  5. ‘null’ • ‘null’ denotes the null reference, a reference which does not refer to any object. • We can use ‘null’ to solve the two dogs, one collar problem (see code on next slide):

  6. removeCollar rather than getCollar public class Dog { private Collar _collar; public Dog(Collar collar) { this._collar = collar; } public void setCollar(Collarcollar) { this._collar= collar; } public Collar removeCollar() { Collar temp = this._collar; this._collar = null; return temp; } }

  7. Can also use in constructor public class Dog { private Collar _collar; public Dog() { _collar = null; } . . . } Now a Dog can be created without a Collar

  8. Consider this code(assume association via constructor) fido rover 3500 4000 Dog fido = new Dog(new Collar()); Dog rover = new Dog(new Collar()); fido – 3500 rover – 4000 fido’s _collar – 3600 rover’s _collar – 4100 two collars are at 4850 and 4925 • 4850 _collar • _collar 3500 3600 4000 4100 • 4925 4850 4925

  9. Consider this code(assume association via constructor) fido rover 3500 4000 temp Dog fido = new Dog(new Collar()); Dog rover = new Dog(new Collar()); fido.setCollar(rover.removeCollar()); public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; } • 4850 _collar • _collar 3500 3600 4000 4100 • 4925 4850 4925

  10. Consider this code(assume association via constructor) fido rover 3500 4000 temp Dog fido = new Dog(new Collar()); Dog rover = new Dog(new Collar()); fido.setCollar(rover.removeCollar()); public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; } • 4850 _collar • _collar 3500 3600 4000 4100 What happens here? Which _collar are we referring to here? • 4925 4850 4925

  11. thisthe object on which a method is invoked fido rover this 3500 4000 temp fido.setCollar(rover.removeCollar()); public Collar removeCollar() { Collar temp = _collar; _collar = null; return temp; } • 4000 • 4925 • 4850 _collar • _collar 3500 3600 4000 4100 What happens here? Which _collar are we referring to here? • 4925 4850 4925

  12. thisimplicitly in code fido rover this 3500 4000 temp fido.setCollar(rover.removeCollar()); public Collar removeCollar() { Collar temp = this._collar; this._collar = null; return temp; } • 4000 • 4925 • 4850 _collar • _collar 3500 3600 4000 4100 What happens here? Which _collar are we referring to here? • 4925 4850 4925

  13. this fido rover this 3500 4000 temp rover.setCollar(fido.removeCollar()); public Collar removeCollar() { Collar temp = this._collar; this._collar = null; return temp; } • 3500 • 4850 • 4850 _collar • _collar 3500 3600 4000 4100 What happens here? Which _collar are we referring to here? • 4925 4850 4925

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