equals() in Wrapper Classes

[Stanislava Trajlov]

I thought equals() method was overriden (ie. was performing "deep" comparison) only in String and Boolean wrapper classes.
Now I encountered an example in Poddar Questions where Double seems to overriding equals() as well...
What is finally the list of all wrapper classes overriding Object's equals() method?
Thank you!!

[Peter den Haan]

All of them do. They implement Comparable as well.
- Peter

[Sadhi Mushrif]

Do equals() method in String class and equals()
method in the Wrapper class have functionality
i.e they compare the actual values and not if the references are same.

[s khosa]

equals() method for a wrapper class also compares whether the operands are of same Wrapper type, other than checking for their contined values.

[Anupam Sinha]

Yes the equals method is overriden in all wrapper classes and String class as well. But remember the StringBuffer class doesnt overrides it. Consider the following code

class test
{
 public static void main (String[] args) {
 Integer i=new Integer("1");
 Integer j=new Integer("1");
 String s=new String("1");
 String s1="1";
 StringBuffer sb=new StringBuffer("1");
 StringBuffer sb1=new StringBuffer("1");
 
 System.out.println(i==j);         //false
 System.out.println(i.equals(j));   //true 
 System.out.println(s==s1);          //false
 System.out.println(s.equals(s1));   //true
 System.out.println(sb==sb1);        //false
 System.out.println(sb.equals(sb1)); //false
 System.out.println(sb==sb);          //true
 System.out.println(sb.equals(sb));   //true
 System.out.println(sb1==sb1);        //true
 System.out.println(sb1.equals(sb1)); //true
 }
}

[Stanislava Trajlov]

OK, so all of the following wrapper classes: Boolean, String, Double, Integer, Float, Byte, Short and Long DO OVERRIDE Object's equals() method (and therefore do "deep" comparios) while it's ONLY StringBuffer class that doesn't override it and for StringBuffer objects equals() and == have the same effect.
Is that right?
Thanks!!!

[Anupam Sinha]

Yes you are right. Yes for StringBuffer == and equals have the same effect. I just included the StringBuffer because I thought that its related to this topic, but StringBuffer is not a wrapper class.

[Stanislava Trajlov]

Thank you all for the help!
Stanislava

[Mocha D'Late]

If StringBuffer does not implement equals, why are the two lines below from your code TRUE !!
System.out.println(sb.equals(sb)); //true System.out.println(sb1.equals(sb1)); //true

[Anupam Sinha]

As StringBuffer does not override the equals() method of the Object class. It has theinherited behaviour of the equals() in the Object. Which simply does a == comparison. So sb==sb and sb1==sb1 will return true and so will the equals method.
As in

System.out.println(sb.equals(sb)); //true System.out.println(sb1.equals(sb1)); //true