I'm stuck with one of the final drills in my java programming course and would appreciate a pointer as to what I should be doing to satisfy the outcomes required.
The code will be tested by the following code which can't be altered:
Test:
int wheels = 4;
String make = "Honda";
String color = "Yellow";
Vehicle v1 = new Vehicle(make);
System.out.println(v1.aboutMe());
Vehicle v2 = new Vehicle(make, color);
System.out.println(v2.aboutMe());
Vehicle v3 = new Vehicle(make, color, wheels);
System.out.println(v3.aboutMe());
Result:
Vehicle object created.
Make: Honda
Colour: Blue
Wheels: 4
Vehicle object created.
Make: Honda
Colour: Yellow
Wheels: 4
Vehicle object created.
Make: Honda
Colour: Yellow
Wheels: 4
The code I have written is here but doesn't compile (temporary solution is greyed out but doesn't meet testing criteria as alters main method to passes parameters from the instance):
public class Vehicle {
// TODO your code goes here
// declare instance fields here!
String make;
String color;
int wheels;
public String aboutMe() {
String statement = "Make: " + make + "\n" + "Colour: " + color + "\n" + "Wheels: " + wheels;
return statement;
}
// constructor method
public Vehicle(String vehicleMake, String vehicleColor, int vehicleWheels) {
make = vehicleMake;
color = vehicleColor;
wheels = vehicleWheels;
}
//Test:
public static void main(String[] args) {
int wheels = 4;
String make = "Honda";
String color = "Yellow";
System.out.println("Vehicle object created.");
//CODE REQUIRED BY TEST:
Vehicle v1 = new Vehicle(make);
//Vehicle vh1 = new Vehicle("Honda", "Blue", 4);
System.out.println(vh1.aboutMe());
//CODE REQUIRED BY TEST:
Vehicle v2 = new Vehicle(make, color);
//Vehicle vh2 = new Vehicle("Honda", "Yellow", 4);
System.out.println(vh2.aboutMe());
//CODE REQUIRED BY TEST:
Vehicle v3 = new Vehicle(make, color, wheels);
//Vehicle vh3 = new Vehicle("Honda", "Yellow", 4);
System.out.println(vh3.aboutMe());
}
//Code stops here
}
In summary, how do I pass the instances declared in the main to the constructor?
Thanks kindly, this is my first post on here so much appreciated for bearing with me while I learn the correct protocol for asking questions on here.
Edit: thanks kindly the code runs now much appreciated
public class Vehicle {
// TODO your code goes here
// declare instance fields here!
String make;
String color;
int wheels;
public String aboutMe() {
String statement = "Vehicle object created.\n" + " Make: " + make + "\n" + " Colour: " + color + "\n" + " Wheels: " + wheels;
return statement;
}
//constructor method
public Vehicle(String vehicleMake, String vehicleColor, int vehicleWheels) {
make = vehicleMake;
color = vehicleColor;
wheels = vehicleWheels;
}
public Vehicle(String make) {
this(make, "Blue");
}
public Vehicle(String make, String color) {
this(make, color, 4);
}
public static void main(String[] args) {
int wheels = 4;
String make = "Honda";
String color = "Yellow";
//System.out.println("Vehicle object created.");
Vehicle v1 = new Vehicle(make);
System.out.println(v1.aboutMe());
Vehicle v2 = new Vehicle(make, color);
System.out.println(v2.aboutMe());
Vehicle v3 = new Vehicle(make, color, wheels);
System.out.println(v3.aboutMe());
}
// Code stops here
}
You need to create other constructors
public Vehicle(String make) {
this(make, "Blue");
}
public Vehicle(String make, String color) {
this(make, color, 4);
}
Related
Is there a way to process each class attribute in parallel using java 8 lambda?
For example, for a given Car.java:
public class Car{
private String color;
private String model;
private float value;
private float tax;
// and others attributes
.
.
.
// Getters and Setters
}
I would like to make some process over color, model, value, tax, etc in parallel. So basically the wished logic would be:
parallel processing:
- color
- model
- value
- tax
then join and update Car.java object instance fields.
Please, note that this problem is independent of the number of cars instances. It could be just one or many.
I was curious, how that would look like. Assuming the restriction holds, that the processing of each of the properties is independent of one another, that would be one way to utilize parallelStream(). But I doubt very much, that this pays off due to the overhead of the parallel machinery. One could make it even more outlandish using reactive streams, e.g. RxJava.
public class Car{
public String color;
public String model;
public float value;
public float tax;
public Car(String color, String model, float value, float tax) {
this.color = color;
this.model = model;
this.value = value;
this.tax = tax;
}
#Override
public String toString() {
return "Car{" +
"color='" + color + '\'' +
", model='" + model + '\'' +
", value=" + value +
", tax=" + tax +
'}';
}
}
#Test
public void process() {
List<Consumer<Car>> processors = Arrays.asList(
c -> c.color = printThread(c.color.toLowerCase()),
c -> c.model = printThread(c.model.toLowerCase()),
c -> c.value = printThread(c.value * c.value),
c -> c.tax = printThread(c.tax / c.tax));
Arrays.asList(new Car("Red", "AlphaGorilla", 1f, 0.5f), new Car("Blue", "Bloated++", 10f, 0.2f))
.parallelStream().forEach(c -> {
System.out.println(c);
processors.parallelStream().forEach(p -> {
p.accept(c);
fakeExpensiveComputation();
});
System.out.println(c);
});
}
private <T> T printThread(T smthg) {
System.out.println(String.format("Calculated value %s in thread %d", smthg.toString(), Thread.currentThread().getId()));
return smthg;
}
private void fakeExpensiveComputation() {
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
throw new RuntimeException();
}
}
I can't figure it out what getExits() needs to be in order to get the output requested by the problem.
//Constructor
public class Room {
private String name;
private String description;
private Room north;
private Room east;
private Room south;
private Room west;
public Room (String name, String description){
this.name = name;
this.description = description;
}
public Room getEast(){
return this.east;
}
public String getExits (){
//
}
public String getName(){
return this.name;
}
public Room getNorth(){
return this.north;
}
public Room getWest(){
return this.west;
}
public Room getSouth(){
return this.south;
}
public void setExits (Room n, Room e, Room w, Room s){
this.north = n;
this.east = e;
this.west = w;
this.south = s;
}
public String toString(){
return String.format("%s\n%s\n%s", this.name, this.description,getExits());
}
}
//Main Method
public class Tester{
public static void main(String []args){
Room hall = new Room ("Hall", "It's Dark");
Room bed = new Room ("Bed", "Tiny Room");
Room bath = new Room ("Bath", "Toilets here");
Room dine = new Room ("Dine", "Table and chairs");
hall.setExits(bed, bath, dine, null);
System.out.println(hall);
}
}
Output expected:
Hall
It's Dark
North: Dine
East: Bath
West: Dining
The 'Object Oriented' way of getting what you want would be to override the toString() method in your Room class such that it returns the name of the room.
You then modify the getExits(), like so:
public String getExits (){
StringBuilder sb = new StringBuilder();
if(this.north != null) sb.append(this.north.toString()).append(" North") else sb.append("No Exit for: North");
...
return sb.toString();
}
....
public class Room {
private String name;
...
#Override
public String toString() {
return this.name;
}
}
exit isn't something you can describe with a String. In the OO world, it should be a reference to a more meaningful object. I would go with
public Collection<Room> getExits();
or
public Map<String, Room> getExits();
which accurately describes where you can get from the hall. Here, we are assuming that "exit" is a doorway to another room.
You could return
Arrays.asList(northRoom, eastRoom, southRoom, westRoom);
or
Map<String, Room> map = new HashMap<>();
map.put("north", northRoom);
...
return map;
Then you would be able to provide any String representation from the returned collection.
It's like a sign placed in the hall to help people navigate. Even though it can be replaced with another sign (a more detailed/accurate one), the structure of the building is constant, and you aren't altering it. You are just representing it differently.
String simpleSign = "You can go to: " + getExits().stream().map(Object::toString).collect(Collectors.join(", "));
or
String detailedSign = "Directions to go: " + getExits().entrySet().stream().map(e -> e.getKey() + " -> " + e.getValue().toString()).collect(Collectors.join("\n"));
Here's one way of doing things. It's a little awkward because you have to check for null for each case - if that's not the case for you, you can remove those checks.
public String getExits (){
List<String> exits = new ArrayList<>();
if (north != null) exits.add("North: " + north.name);
if (south != null) exits.add("South: " + south.name);
if (east != null) exits.add("East: " + east.name);
if (west != null) exits.add("West: " + west.name);
return String.join("\n", exits);
}
I have an Object ArrayList and I need to use the toString() method of the Motor object, which is a parameter of the Vehicle object. My vehicle objects are in an ArrayList which is iterated through with a for-loop (I know a foreach loop would be easier, but this is part of the assignment)
Here is the code for the loop:
for (int i = 0; i < VehicleList.size(); i++) {
System.out.println();
String info = VehicleList.get(i).toString();
Motor m = VehicleList.get(i).motor;
String motorInfo = m.toString();
System.out.println(info);
System.out.println(m);
}
There is an error that says "motor cannot be resolved or is not a field".
All of the classes should allow this to work, unless of course there is a simple mistake I am missing.
Here is the Motor class:
public class Motor {
protected String name;
protected int cylinders;
protected int bhp;
protected double displacement;
public Motor(String name, int cylinders, int bhp, double displacement) {
this.name = name;
this.cylinders = cylinders;
this.bhp = bhp;
this.displacement = displacement;
}
public String toString() {
return "Motor name= " + name + ", cylinders= " + cylinders + ", bhp=
" + bhp + ", displacement= " + displacement;
}
}
Motors and Vehicles are intitialized here (In the TestVehicle class):
//Motors
Motor EcoBoost = new Motor("EcoBoost", 6, 310, 2.3);
Motor Hemi = new Motor("Hemi", 8, 707, 5.7);
Motor P90D = new Motor("P90D", 0, 762, 0.0);
//Vehicles
Vehicle v0 = new PassCar("Ford", "Mustang", 2016, 44500.0, 5, true, EcoBoost);
Vehicle v1 = new PassCar("Tesla", "Model S", 2016, 121000.0, 2, true, P90D);
Vehicle v2= new Truck("Dodge", "Ram", 2016, 46000.0, "pickup", 1500, Hemi);
PassCar and Truck are inherited classes of Vehicle with a few more attributes. I can post the PassCar or Truck class if needed but I do not think that is where the problem is arising from. I believe it is coming from the For-Loop, specifically the line Motor m = VehicleList.get(i).motor; but I am not sure of how to fix it.
Vehicle Class:
public class Vehicle {
protected String make;
protected String model;
protected int year;
protected double price;
public Vehicle(String make, String model, int year, double price) {
this.make = make;
this.model = model;
this.year = year;
this.price = price;
}
public void description() {
System.out.println("Description");
}
public String toString() {
return "make= " + make + ", model= " + model + ", year= " + year +
", price= " + price;
}
}
EDIT: There cannot be any Getters or Setters as per the assignment requirements, and it must be an ArrayList, not a regular List. When I switch to I get the error "Type mismatch: cannot convert from ArrayList to ArrayList
Here is an image of the classes:
ArrayList<Object> VehicleList = new ArrayList<>(Arrays.asList(vehicles));
VehicleList is declared to contain instances of Object, so the compiler will only let you access methods and fields it knows exist on all instances of Object.
Change it to ArrayList<Vehicle>.
First, mind the naming convention. Variables should be named in camcelCase e.g. vehicleListinstead ofVehicleList`
I have an Object ArrayList
I believe you mean declaration of vehicleList looks like ArrayList<Object> vehicleList
Then behavior is expected because compiler only knows that VehicleList.get(i) is going to return you an Object reference. It can be a Vehicle, but it can also be anything else. So it won't allow you to access the motor field, as there is simply no such field in Object.
Change your declaration to something like List<Vehicle> vehicleList
However, as mentioned in other answer, it is not a good idea to access the field directly because of various reason. A slightly less evil way is to have getter of motor. (A better way is to provide meaningful behaviors instead of providing access to internal data)
Create an interface IMotor which is used by Vehicle class and Implemented in PassCar and other implementation of vehicle.
IMotor.java
public interface IMotor {
public Motor getMotor();
}
Motor.java
public class Motor {
protected String name;
protected int cylinders;
protected int bhp;
protected double displacement;
public Motor(String name, int cylinders, int bhp, double displacement) {
this.name = name;
this.cylinders = cylinders;
this.bhp = bhp;
this.displacement = displacement;
}
public String toString() {
return "Motor name= " + name + ", cylinders= " + cylinders + ", bhp=" + bhp + ", displacement= " + displacement;
}
}
Vehicle.java
public abstract class Vehicle implements IMotor{
protected String make;
protected String model;
protected int year;
protected double price;
public Vehicle(String make, String model, int year, double price) {
this.make = make;
this.model = model;
this.year = year;
this.price = price;
}
public String toString() {
return "make= " + make + ", model= " + model + ", year= " + year +
", price= " + price;
}
}
PassCar
public class PassCar extends Vehicle{
protected Motor motor;
public PassCar(String make, String model, int year, double price, Motor motor) {
super(make, model, year, price);
this.motor = motor;
}
public Motor getMotor() {
return motor;
}
}
Test.java
import java.util.Arrays;
import java.util.List;
public class Test {
public static void main(String[] args) {
Motor EcoBoost = new Motor("EcoBoost", 6, 310, 2.3);
Vehicle v0 = new PassCar("Ford", "Mustang", 2016, 44500.0, EcoBoost);
List<Vehicle> vehicles = Arrays.asList(v0);
System.out.println(vehicles.get(0).getMotor());
}
}
Your problem is that motor is not a member of the Vehicle class, but you are trying to access it through an expression of type Vehicle - namely vehicleList.get(i). This is forbidden, because the compiler has no way of knowing that every possible kind of Vehicle has a motor. After all, what would happen if you added a Bicycle class?
To make this work, you should remove motor from the Truck and PassCar classes, and add it to the Vehicle class. That way, vehicleList.get(i).motor would actually make sense, since the Vehicle expression would be guaranteed to refer to a Vehicle with a Motor.
It would also be recommended to use a getter for the motor field - that is, have motor as a private field of the Vehicle class, and write a method getMotor() to return it. You could then write vehicleList.get(i).getMotor() to get the Motor object associated with one Vehicle in the list.
Thanks to the help of all of your comments and my Java textbook, I managed to piece it together. Here is how I got it to work:
for (int i = 0; i < vehicleList.size(); i++) {
String motorInfo = "";
String info = "";
System.out.println();
if (vehicleList.get(i) instanceof PassCar) {
info = ((PassCar)vehicleList.get(i)).toString();
**motorInfo = ((PassCar)vehicleList.get(i)).motor.toString();**
}
else if(vehicleList.get(i) instanceof Truck) {
info = ((Truck)vehicleList.get(i)).toString();
**motorInfo = ((Truck)vehicleList.get(i)).motor.toString();**
}
Basically I had to use a polymorphic call and check if it was an instance of a PassCar or Truck.
And as for the Array and ArrayList used during the Class, I edited them like this:
Vehicle [] vehicles = new Vehicle [3];
vehicles[0] = v0;
vehicles[1] = v1;
vehicles[2] = v2;
showVehicle(vehicles);
ArrayList<Vehicle> vehicleList = new ArrayList<Vehicle>(Arrays.asList(vehicles));
System.out.println();
System.out.println("Output from ArrayList in main: ");
Thank you for the help everyone!
Ok so I'm trying to get a better understanding of how to return a private variable from a class that I have created. I've only provided a small snippet of my main program to explain my question, so if more information is needed please let me know. My goal is to return a string from the class (working great), but also be able to return the private variables individually as needed (example used below is "flight_number").
public class Flights {
private String dest_city, dest_state, departureDate, departureTime;
private int flight_number;
public Flights(String city, String state, String dDate, String dTime, int flightNumber) {
dest_city = city;
dest_state = state;
departureDate = dDate;
departureTime = dTime;
flight_number = flightNumber;
}
public String toString() {
return "Flight number: " + flight_number + " Destination: " + dest_city + "," + dest_state + " Departing on:" + departureDate + " at" + departureTime + ".";
}
}
public class dummy {
public static void main(String[] args) {
// Uses the constructor to set values
Flights flight1 = new Flights("Houston", "Texas", "12/20/2014", "12:40 pm", 100);
System.out.println(flight1);
System.out.println(flight_number); // Error: `flight_number` cannot be resolved to a variable.
}
}
You need to add a public getter in Flights and call it from main:
public class Flights {
// all the private fields
public int getFlightNumber() {
return this.flight_number;
}
}
In Main:
public static void main(String[] args) {
Flights flight1 = new Flights("Houston", "Texas"); //...
System.out.println(flight1);
System.out.println(flight1.getFlightNumber()); // call the getter
}
You should start with an editor like eclipse and that should help you get started quickly. Getters and Setters is what you need, but start with Eclipse and you should do better.
Im trying to get help with to run with my automobile compiler I chaned a few things and i have 1 error
public class AutomobileDescription
{
/**
Constructor to display the make, model and price the new automobile I wish to purchase
*/
public AutomobileDescription(String carMake, String carModel, carPrice)
{
make = m;
model = mo;
price = p;
}
public String m =("Toyota");
public String mo =("Camry");
public String p =("22055");
public String getAutomobileinfo()
{
return m + mo + p;
Automobile myAutomobile = new Automobile(Toyota, Camry, 22055);
System.out.println("The Make, Model and Price of the car is: m + mo + p ");
}
}
----jGRASP exec: javac -g AutomobileDescription.java
AutomobileDescription.java:7: error: expected
public AutomobileDescription(String carMake, String carModel, carPrice)
^
1 error
----jGRASP wedge2: exit code for process is 1.
----jGRASP: operation complete.
You have multiple problems here:
public class AutomobileDescription
{
/**
Constructor to display the make, model and price the new automobile I wish to purchase
*/
public AutomobileDescription(String carMake, String carModel, /*no return type*/ carPrice)
{
make = m;
model = mo;
price = p;
}
public String m =("Toyota");
public String mo =("Camry");
public String p =("22055");
public String getAutomobileinfo()
{
return m + mo + p; /*return? then why statements after this?*/
Automobile myAutomobile = new Automobile(Toyota, Camry, 22055);
System.out.println("The Make, Model and Price of the car is: m + mo + p ");
}
}
Solution:
public class AutomobileDescription{
/**
Constructor to display the make, model and price the new automobile I wish to purchase
*/
public AutomobileDescription(String carMake, String carModel, String carPrice)
{
m = make;
mo = model;
p = carPrice;
}
private String m;
private String mo;
private String p;
public String getAutomobileinfo()
{
return m + mo + p;
}
public static void main(String[] args){
AutomobileDescription myAutomobile = new AutomobileDescription("Toyota", "Camry", "22055");
System.out.println("The Make, Model and Price of the car is: " + myAutomobile.getAutomobileinfo());
}
}
public AutomobileDescription(String carMake, String carModel, carPrice)
^^^^^^^^
You have omitted the type of parameter carPrice. Most likely you want
public AutomobileDescription(String carMake, String carModel, BigDecimal carPrice)
Another problem...
public String getAutomobileinfo()
{
return m + mo + p;
Automobile myAutomobile = new Automobile(Toyota, Camry, 22055);
System.out.println("The Make, Model and Price of the car is: m + mo + p ");
}
The return statement means that the two following statements can never be reached, and this will result in a compile error after you correct the first problem.
This is not a valid method name:
public String getMake + getModel + getPrice;
Fix that. If you still have problems, be a little more detailed. Maybe even post the error message!