object-comparison

I have a program that is zoo and in the zoo there are branched subgroups of animals that are reptiles. When I do an equals method the main program compiles and it runs. I'm confused how does java know to use the equals method if I'm comparing objects and not specifically int or String? public class Zoo { public static void main(String[]args) { Animal a=new Animal("Bob"); Reptile komodo= new Reptile("Snakey"); komodo.bask(); a.size=3; komodo.size=5; System.out.println(a); System.out.println(komodo); Turtle t= new Turtle("Slowy"); t.hide(); t.size=6; t.numlegs=4; System.out.println(t); System

Does in_array() do object comparison where it checks that all attributes are the same? What if $obj1 === $obj2 , will it just do pointer comparison instead? I'm using an ORM, so I'd rather loop over the objects testing if $obj1->getId() is already in the array if it does object comparison. If not, in_array is much more concise. in_array() does loose comparisons ( $a == $b ) unless you pass TRUE to the third argument, in which case it does strict comparisons ( $a === $b ). Semantically, in_array($obj, $arr) is identical to this: foreach ($arr as &$member) { if ($member == $obj) { return TRUE; }

I've read everywhere that when you define an Integer between -128 to 127 in Java, instead of creating a new object it returns an object already created. I don't see any point of doing this other than letting newbie programmers compare Integer objects with == to see if they are the same number, but I think this is bad because sure they think that they can compare any Integer with == , and also is teaching a bad practice in any programming language: comparing the content of two 'different' objects with == . Is there any other reason on why this is done? Or is it just a bad decision when

This question already has an answer here: How to properly compare two Integers in Java? 8 answers I have to compare two Integer objects (not int ). What is the canonical way to compare them? Integer x = ... Integer y = ... I can think of this: if (x == y) The == operator only compares references, so this will only work for lower integer values. But perhaps auto-boxing kicks in...? if (x.equals(y)) This looks like an expensive operation. Are there any hash codes calculated this way? if (x.intValue() == y.intValue()) A little bit verbose... EDIT: Thank you for your responses. Although I know

This question already has an answer here: About the changing id of an immutable string 5 answers Why does "hello" is "hello" produce True in Python? I read the following here : If two string literals are equal, they have been put to same memory location. A string is an immutable entity. No harm can be done. So there is one and only one place in memory for every Python string? Sounds pretty strange. What's going on here? carl Python (like Java, C, C++, .NET) uses string pooling / interning. The interpreter realises that "hello" is the same as "hello", so it optimizes and uses the same location