Java ArrayList Contain always return false although it contain the same value

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You need to override the equals method herited from the Object class (and hence also hashCode to respect the contract, see Why do I need to override the equals and hashCode methods in Java? ) in your Hole class.

Returns true if this list contains the specified element. More
formally, returns true if and only if this list contains at least one
element e such that (o==null ? e==null : o.equals(e)).

Basically the default equals implementation is an == comparison between the two objects 

public boolean equals(Object obj) {
   return (this == obj);
}

Since you created two different objects, while they have the same value as attributes they’re two distincts objects and hence this == obj returns false.

If you did :

Hole a = new Hole(0,1);
leftFlowInnerHole.add(a);
System.out.print(leftFlowInnerHole.contains(a));

You’ll see that it outputs true.

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