Card for a car object:
Consider a “Car” class, which simulates fuel consumption in a car.
On the front side of the card, the methods that the object can execute are written. The methods for efficiency, adding gas, driving a given distance, and checking the amount of gas left in the tank that is as follows:
Car myCar Car(mpg) addGas(amount) drive(distance) getGasLeft |
On the back side of the card, the values of the instance variables are noted down. After creating the objects, the values of the instance variables will be as follows:
gasLeft | milesPerGallon |
0 | 25 |
Here, the initial value of “gasLeft” will be zero and the efficiency calculated in miles per gallon will be 25mpg.
Tracing the methods of Self Check 32:
The following method calls are given:
//Call the methods
Car myCar(25);
myCar.addGas(20);
myCar.drive(100);
myCar.drive(200);
myCar.addGas(5);
Cross out the old values whenever a mutator method is called, and write down the new one below.
gasLeft | milesPerGallon |
13 | 25 |
- Initially, the value of “gasLeft” and “milesPerGallon” was “0” and “25” respectively.
- When the method myCar.addGas(20)is called, the value “0” is cut-off and the value of “gasLeft” will be updated to “20”.
- It is because the addGas method adds the value of gas and thus, the gas left will be 0+20=20.
- When the method myCar.drive(100)is called, the value “20” is cut-off and the value of “gasLeft” will be updated to “16”.
- It is because a gas of value “4” is required to travel a distance of “100miles” and thus, the gas left will be 20-4=16.
- When the method myCar.drive(200)is called, the value “16” is cut-off and the value of “gasLeft” will be updated to “8”.
- It is because a gas of value “8” is required to travel a distance of “200miles” and thus, the gas left will be 16-8=8.
- When the method myCar.addGas(5)is called, the value “8” is cut-off and the value of “gasLeft” will be updated to “13”.
- It is because the addGas method adds the value of gas and thus, the gas left will be 8+5=13.
Instance variable added in Self Check 33:
It is given that the odometer of the car is simulated by adding a method “getMilesDriven”.
After adding the instance variables to the card, the card will be as follows:
gasLeft | milesPerGallon | totalMiles |
0 | 25 | 0 |
The initial value of the variable “totalMiles” is assigned to zero.
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