Java - Finding the element of an array given the value?

Question

In my Java program, I am simulating a parking garage. Suppose there are a random number of cars, let's say 7. Car number 1 is referred to by the value 1, car 2 is referred to by the value 2, and so on. Each car value is randomly stored in an array that represents the parking garage. Each element of the array represents a parking spot. I am trying to write a method that does the following: Suppose you want to know what parking space car number 4 is in. The value "4" is passed to the method, and the method will search the array for that value. I want the method to tell me which element of the array the value "4" was found in. Here is what I have so far for the method:

public int findBayOfCar(int carNumber)
{
    int index = -1;
    boolean found = false;

    while (!found)
    {
        if (cars[index] == carNumber)
        {

        }
        index++;
    }

}

Obviously it will not work because Java cannot compare cars[index] (which is an array of the Car type) to carNumber, which is an int. What can I do to correct this?

what is 'cars' type. Is it its own class? Then you either have a getter method mentioned previously or a public variable you can access. Please post the code for how you set the value of each carNumber and we can help probably. — napkinsterror
– napkinsterror, Commented Dec 9, 2015 at 23:44

Orel Eraki · Accepted Answer · 2015-12-09 23:53:03Z

3

You had many errors in such a small code.

while (!found) this means that you will continue searching until you found something, but what happens if the element we're searching is not on the array ? We will get the infamous ArrayOutOfBoundsException due the fact we will try to access non-existing array cell. Solution: for (int i = 0; i < cars.length; i++) in order to run from the start until the size of the array.
Found, now what ? you didn't stopped when finding the car you were looking for, now we're setting it as found = true and stopping the search.

Code:

public int findBayOfCar(int carNumber)
{
    int foundAtBay = -1;
    for (int i = 0; i < cars.length; i++)
    {
        if (cars[i].number == carNumber) // or whatever .Number or .number which identify the car number.
        {
            foundAtBay = i;
            break;
        }
    }
    return foundAtBay;
}

edited Dec 9, 2015 at 23:53

answered Dec 9, 2015 at 23:46

Orel Eraki

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1 Comment

Stephen P Over a year ago

You don't want to return a boolean found, you want to return the bay number in which the car was found.

MaxZoom · Accepted Answer · 2015-12-09 23:45:55Z

1

You should of reference your Car object to obtain its number:

public static int findBayOfCar(int carNumber, Car[] cars)
{
  int index = -1;
  boolean found = false;

  while (!found && index < cars.length -1)
  {
    index++;
    if (cars[index].getNumber() == carNumber)
    {
       found = true;
    }  
  }
  return found ? index : -1;
}

answered Dec 9, 2015 at 23:45

MaxZoom

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Comments

Community · Accepted Answer · 2015-12-10 00:15:23Z

1

A simple and a brute-force solution to it would be LinearSearch:

for(int i=0; i < your_array_length; i++){
    if(cars[i] == carNumber){
      return i;
    }
}
return -1; //-1 represents that the car was not parked in any of the slots

edited Dec 10, 2015 at 0:15

CommunityBot

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answered Dec 9, 2015 at 23:52

Sharanya

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1 Comment

Klitos Kyriacou Over a year ago

Omit the break; after the return as it's unreachable.

steffen · Accepted Answer · 2015-12-10 00:13:51Z

If your cars are just numbers, then:

int[] cars = new int[] { 1, 2, 3 } ;
public int indexOf(int carNumber) {
    return Arrays.binarySearch(cars, carNumber);
}

If your cars are strings, then

String[] cars = new String[] { "car1", "car2", "car2" };
public int indexOf(int carNumber) {
    return Arrays.asList(cars).indexOf("car" + carNumber);
}

If your cars are objects, then

Car[] cars = new Car[] { new Car(), new Car(), new Car()  };
public Car indexOf(int carNumber) {
     return IntStream.range(0, cars.length).filter(c -> carNumber == cars[c].number).mapToObj(i -> cars[i]).findFirst().orElse(null);
}

Or, with an ordinary loop:

Car[] cars = new Car[] { new Car(), new Car(), new Car() };
public int indexOf(int carNumber) {
    for (int i = 0; i < cars.length; i++) {
        if (cars[i].number == carNumber) {
            return i;
        }
    }
    return -1;
}

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