Lecture Lab - Pump

class Pump {
  public static final int COST_PER_LITRE = 1.45;

  // REQUIRES: 10 * COST_PER_LITRE  <= amount 
  //		   <= 30 * COST_PER_LITRE 
  // EFFECTS: payment is recorded 
  void prePay(int amount) {
     // stub
  }

  // EFFECTS: returns at least 10 litres of gas
  int dispense() {
     return 0;  // stub
  }
}

class APump extends Pump {
  // REQUIRES: 5 * COST_PER_LITRE  <= amount
  //		   <= 30 * COST_PER_LITRE 
  // EFFECTS: payment is recorded 
  void prePay(int amount) {
  // stub  
  }

  // EFFECTS: returns at least 5 litres of gas
  int dispense() {
     return 0;  // stub   
  }
}

class BPump extends Pump {
  // REQUIRES: 20 * COST_PER_LITRE  <= amount
  //		   <= 30 * COST_PER_LITRE 
  // EFFECTS: payment is recorded 
  void prePay(int amount) {
   // stub 
  }
  // EFFECTS: returns at least 20 litres of gas
  int dispense() {
     return 0;  // stub   
  }
}

Is precondition narrower?

Is postcondition wider?

Is LSP violated?

N-N-N

N-Y-Y

Y-N-Y

N-N-N

No good substitute if LSP is violated!

?-?-?

Lecture Lab - Speed

//EFFECTS: returns a speed of 1.0, 1.5, 2.0, 2.5 or 3.0
public double computeSpeed() {
  return 1.0;// stub
}

Is postcondition wider?

//EFFECTS: returns a speed of 1.0, 2.0 or 3.0

//EFFECTS: returns a speed in the range 1.0 to 1.5 or in the range 2.5 to 3.0

//EFFECTS: returns a speed of 0.0, 1.0, 2.0 or 3.0

//EFFECTS: returns a speed of 1.5 or 2.5

Lecture Lab - Choice

//REQUIRES: choice is one of "a", "b", "c" or "d"
//EFFECTS: (omitted)
public void handleChoice(String choice) {
  // stub
}

Is precondition narrower?

//REQUIRES: choice is one of "A", "B", "C" or "D"

//REQUIRES: choice is one of "a", "b", "c", "d", "e"

//REQUIRES: choice is one of "b", "c", "d", "e", "f", "g"

//REQUIRES: choice is one of "a", "A", "b", "B", "c", "C", "d" or "D"

//REQUIRES: choice is one of "a", "b", "c"