How does a ArrayList's contains() method evaluate objects?

Question

Say I create one object and add it to my ArrayList. If I then create another object with exactly the same constructor input, will the contains() method evaluate the two objects to be the same? Assume the constructor doesn't do anything funny with the input, and the variables stored in both objects are identical.

ArrayList<Thing> basket = new ArrayList<Thing>();   Thing thing = new Thing(100);   basket.add(thing);   Thing another = new Thing(100);   basket.contains(another); // true or false? 

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class Thing {       public int value;        public Thing (int x) {         value = x;     }      equals (Thing x) {         if (x.value == value) return true;         return false;     } } 

Is this how the class should be implemented to have contains() return true?

Answer 1

ArrayList implements the List Interface.

If you look at the Javadoc for List at the contains method you will see that it uses the equals() method to evaluate if two objects are the same.

Answer 2

I think that right implementations should be

public class Thing {     public int value;        public Thing (int x)     {         this.value = x;     }      @Override     public boolean equals(Object object)     {         boolean sameSame = false;          if (object != null && object instanceof Thing)         {             sameSame = this.value == ((Thing) object).value;         }          return sameSame;     } }