Comparing String and Integer with equals

Question

The output of the below code is false

String str = "3456";
String str1 = "3456";
System.out.println(Integer.valueOf(str).equals(str1));

I didn't understand it. I thought it will return true. As I am preparing for SCJP, understanding the reason behind it may be helpful. Can someone please help?

Answer 1

An Integer will never be equal to a String.

Both classes have very strict equals() definitions that only accept objects of their respective types.

• Integer.equals():

  The result is true if and only if the argument is not null and is an Integer object that contains the same int value as this object.

• String.equals():

  The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object.

That's actually a quite common way to implement equals(): only objects of the same class (and occasionally subclasses) can be equal. Other implementations are possible, but are the exception.

One common exception are the collections such as List: every List implementation that follows the convention will return true when compared to any other implementation, if it has the same content in the same order.