Java – Storing object into an array – Java

arraysjavastoring-data

I am relatively new to Java and I have taken some light courses on it. I am trying to emulate an exercise that I had a while back and I am having some trouble.

I have two classes. One is taking in data and the other is storing it.

public class Car{

public Car(String name, String color)
{
     this.name = name,
     this.color = color
}

How can I store this into the array (not an array list) that I created in this class:

public class CarDatabase {

Car[] carList = new Car[100];

public CarDatabase()
{
    // System.out.println("test");
}

public void createAccount(String name, String color)
{        
// this is where I am having trouble


    for (int i = 0; i < carList.length; i++)
    {

    System.out.println("Successfully created: " + name + 
            "." + "Color of car: " + color);
    break;


    }
}

I don't have a main method yet but I will need one later on to for example, PRINT out this array and that is what I can't wrap my head around – how do I store DATA/OBJECTS into the "CarDatabase" array so I can call methods with it later (instead of just being able to print it)?

Any help would be appreciated.
Thanks!

Best Answer

Not really sure what you are trying to achieve but I'll give it a go.

You could modify your CarDatabase class like so -

public class CarDatabase {

  Car[] carList = new Car[100];
  int carsStored;

  // No need for a constructor since we don't need any initialization.
  // The default constructor will do it's job.

  public void createAccount(String name, String color) {
    carList[carsStored++] = new Car(name, color);
  }
}

And your main method could look like -

public static void main(String[] args) {
  CarDatabase database = new CarDatabase();
  database.createAccount("Lambo", "Red");
  database.createAccount("Punto", "White");

  // To loop through your database, you can then do
  for(int i = 0; i < database.carList.length; i++) {
    Car car = database.carList[i];
    // Now you can call methods on car object.
  }
}

Hope that helps.

Related Solutions

Java – Is Java “pass-by-reference” or “pass-by-value”

Java is always pass-by-value. Unfortunately, when we deal with objects we are really dealing with object-handles called references which are passed-by-value as well. This terminology and semantics easily confuse many beginners.

It goes like this:

public static void main(String[] args) {
    Dog aDog = new Dog("Max");
    Dog oldDog = aDog;

    // we pass the object to foo
    foo(aDog);
    // aDog variable is still pointing to the "Max" dog when foo(...) returns
    aDog.getName().equals("Max"); // true
    aDog.getName().equals("Fifi"); // false
    aDog == oldDog; // true
}

public static void foo(Dog d) {
    d.getName().equals("Max"); // true
    // change d inside of foo() to point to a new Dog instance "Fifi"
    d = new Dog("Fifi");
    d.getName().equals("Fifi"); // true
}

In the example above aDog.getName() will still return "Max". The value aDog within main is not changed in the function foo with the Dog "Fifi" as the object reference is passed by value. If it were passed by reference, then the aDog.getName() in main would return "Fifi" after the call to foo.

Likewise:

public static void main(String[] args) {
    Dog aDog = new Dog("Max");
    Dog oldDog = aDog;

    foo(aDog);
    // when foo(...) returns, the name of the dog has been changed to "Fifi"
    aDog.getName().equals("Fifi"); // true
    // but it is still the same dog:
    aDog == oldDog; // true
}

public static void foo(Dog d) {
    d.getName().equals("Max"); // true
    // this changes the name of d to be "Fifi"
    d.setName("Fifi");
}

In the above example, Fifi is the dog's name after call to foo(aDog) because the object's name was set inside of foo(...). Any operations that foo performs on d are such that, for all practical purposes, they are performed on aDog, but it is not possible to change the value of the variable aDog itself.

For more information on pass by reference and pass by value, consult the following SO answer: https://stackoverflow.com/a/430958/6005228. This explains more thoroughly the semantics and history behind the two and also explains why Java and many other modern languages appear to do both in certain cases.

Java – Create ArrayList from array

new ArrayList<>(Arrays.asList(array));

Best Answer

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Java – Is Java “pass-by-reference” or “pass-by-value”

Java – Create ArrayList from array

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