HashMap with Integer as a key

[Vadym Baranenko]

Hi folks,
during the reading of Java documentation I found one interesting thing about the collections. Wrapper classes do not override equals method. So it sepouseto mean that it's impossible to use them as a keys to map. I found this interesting because I use wrappers before and thay seems work fine. So I wrote simple test code:

public static void main(String[] args) {

	Integer in = new Integer(267454564);
	Integer in2 = new Integer(267454564);
	HashMap<Integer,String> testMap = new HashMap<Integer, String>();
	testMap.put(in, "one");
	testMap.put(in2, "two");

	//I was expected that it will be 2
	System.out.println("Test map size: "+testMap.size());
	//It sepouse to return NULL but it do'nt do this! 
	System.out.println("Get the element"+testMap.get( new Integer(267454564)));
		
	//After first 2 lines i was sure that this will be TRUE
	System.out.println(in.equals(in2));
	System.out.println(in.hashCode());
	System.out.println(in2.hashCode());
	}

And now I feel like a fool

[Mohamed Sanaulla]

If you happened to check the source of the Integer.java wrapper class, you can find that the equals method has been overridden to check that both the Integer objects have same int value.

[Vadym Baranenko]

Mohamed Sanaulla wrote:If you happened to check the source of the Integer.java wrapper class, you can find that the equals method has been overridden to check that both the Integer objects have same int value.

Yes, you are right. After posting this topic I go to source code and found this line"

  763       public boolean equals(Object obj) {
  764           if (obj instanceof Integer) {
  765               return value == ((Integer)obj).intValue();
  766           }
  767           return false;
  768       }

It was mistake in the book i reading now and a mistake in my code. Double mistake confused me.