CODEWITHSUNDEEP
javalistcollectionscontains
Nikita Kalugin
Nikita Kalugin

Reputation: 742

Using Contains for objects in List collection

I'm trying to find an object in the List collection by his name using Contains method, but, somehow, it doesn't work. How should I use it?

This is how I try to use this

CandyDao.getAllCandys().contains("Caramel")

But it can't find an object which I need.

CandyDao.java

public class CandyDao {
  private List<Candy> candys = Arrays.asList(new Candy("Caramel", 3, false),
          new Candy("Marmelade", 2, true));

  public List<Candy> getAllCandys(){
    return candys;
  }
}

Candy.java

  public class Candy {
  private String name;
  private float price;
  private boolean InStock;

  public Candy() {
  }

  public Candy(String name, float price, boolean InStock) {
    setName(name);
    setPrice(price);
    setInStock(InStock);
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public float getPrice() {
    return price;
  }

  public void setPrice(float price) {
    this.price = price;
  }

  public boolean getInStock() {
    return InStock;
  }

  public void setInStock(boolean InStock) {
    this.InStock = InStock;
  }
}

Upvotes: 1

Views: 287

Answers (4)

Andreas
Andreas

Reputation: 159260

Since the list contains Candy objects, the contains() method needs a Candy object for the comparison, so you can't use contains("Caramel").

To check if the list contains a Candy object with a name of "Caramel", you can use Java 8+ Streams to do the search:

CandyDao.getAllCandys().stream().Map(Candy::getName).anyMatch("Caramel"::equals);

The equivalent non-stream version would be:

boolean hasCaramel = false;
for (Candy candy : CandyDao.getAllCandys()) {
    if ("Caramel".equals(candy.getName())) {
        hasCaramel = true;
        break;
    }
}

Upvotes: 3

H&#252;lya
H&#252;lya

Reputation: 3433

getAllCandys() method returns a list of Candyobjects. You should look each element's nameproperty on the list. So cis an element of candyslist. Use c.getName().contains("Caramel") to look for "Caramel"

for(Candy c : candys) {
            System.out.println(c.getName() + " contains? " + c.getName().contains("Caramel"));
        }

Upvotes: 0

Pankaj Singhal
Pankaj Singhal

Reputation: 16053

Override the equals & hashcode method like below :

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    Candy candy = (Candy) o;
    return Objects.equals(name, candy.name);
}

@Override
public int hashCode() {
    return Objects.hash(name);
}

Now, Since the equals function only checks name for equality of Candy object, the following should work:

CandyDao.getAllCandys().contains(new Candy("Caramel", 0, true)) .   //2nd & 3rd arg of Candy constructor are inessential/dummy

Upvotes: 2

Vinoth A
Vinoth A

Reputation: 1239

You should override the Object#equals method in Candy as shown below:

@Override
public boolean equals(Object o) {
    if (!(o instanceof Candy)) {
        return false;
    }

    Candy that = (Candy) o;

    return Objects.equals(that.getName(), this.getName());
}

After overriding, List#contains should return true if the name matches.

Upvotes: 0

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