How to compare user input to an instance variable of all objects from a class

Question

So, I'm trying to compare a string to an instance variable of another class, and I can't think of a way to do this for all objects of the said class. I know for sure that if the method where this occurs is running, I have 4 objects of the class that contains the instance variable. The goal is to compare the string the user gives me, and if it is equal to the one of a previously defined object, change another instance variable in that object. In sudo-code it would be something like this:

if (colourInput == colourofAnyObjectOfTheClass)
   sizeOfThatObject = sizeInput;
else
   new Object(colourInput, sizeInput);

And I've previously defined what colourInput and sizeInput are. How can I go about implementing this in Java?

possible duplicate of [Java string comparison?](http://stackoverflow.com/questions/995918/java-string-comparison) — upog, Nov 04 '13 at 13:14

score 1 · Answer 1 · edited May 23 '17 at 11:51

1

When comparing Strings, you should use the String#equals() method, not the == operator.

if (colourofAnyObjectOfTheClass.equals(colourInput)) {
    sizeOfThatObject = sizeInput;
} else {
    new SomeObject(colourInput, sizeInput);
}

edited May 23 '17 at 11:51

Community

1
1

answered Nov 04 '13 at 13:12

Konstantin Yovkov

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3

and always nice to put the constant in front – Simon Verhoeven Nov 04 '13 at 13:13
Why is using .equals() a better solution? – uname22 Nov 04 '13 at 15:40
Because `.equals()` checks the **contents** of the objects for equality, while the `==` operator checks whether the variables refer the same object in the memory. Check out [this thread](http://stackoverflow.com/questions/995918/java-string-comparison) – Konstantin Yovkov Nov 04 '13 at 15:51

score 0 · Answer 2 · answered Nov 04 '13 at 13:19

You should consider creating some sort of repository of instances of your class that is class which will manage creation of object so it can keep track of them.

class MyEntityRepository {
    private List<MyEntity> entities;

    public MyEntity createOrUpdate(String color, Integer size) {
         MyEntity entity = findByColor(color);
         if (entity != null) {
             entity.setSize(size); 
         } else {
             entity = new MyEntity(color, size);
             entities.add(entity);
         }
         return entity;
    } 

    private MyEntity findByColor(String color) { ... }
}

If you have a lot of entities you may create some sort of index, for example store Map<String, MyEntity> which maps keys to entities and use it to speed up search.

How to compare user input to an instance variable of all objects from a class

2 Answers2