Problem with contains() method in ArrayList

[Chanchal]

hi,
In an application i'm developing, i have a class say X and
an arraylist of X ie,

list = new ArrayList<X>() ;

and i have added an object of X into list

list.add(x); // x ib object of X

and i'm calling the contains() function of the arraylist to check if an
object of X, say 'y' is in there.

I have overridden the equals() method in X and it returns true for
x.equals(y).

But the contains() method returns false. what could be the reason.
please advice

Chanchal

 

[Torkel Franzen]

I have overridden the equals() method in X and it returns true for
x.equals(y).

But the contains() method returns false. what could be the reason.

That you haven't in fact overridden equals.

 

[Chanchal]

Hi Franzen,
i haven't fully understood your comment that i haven't overridden
equals

this is my equals() function

public boolean equals(SaleItem saleItem){
return (saleItem instanceof Service &&
this.name.equals(saleItem.getName()));
}

am i missing anything here??

Chanchal

 

[Jean-Francois Briere]

The equals method MUST have the following signature:

public boolean equals(Object obj)

Regards

 

[Jean-Francois Briere]

this is my equals() function

public boolean equals(SaleItem saleItem){
return (saleItem instanceof Service &&
this.name.equals(saleItem.getName()));
}

Here you are overloading the equals method (same name, different
parameter number / type).
You are not overriding it (same name, same parameter number / type).

Regards

 

[Chanchal]

oooooooppppsssssssss, silly me,

thankx pal

Chanchal

 

[Thomas Hawtin]

The equals method MUST have the following signature:

public boolean equals(Object obj)

Adding @Override to methods that are supposed to override will cause the
compiler to catch these sorts of errors.

Tom Hawtin

 

[Chanchal]

hi thomas

thanks for that tip. but where should i add @Override? should the
signature of function be

@override public boolean equals(Object obj) ? where can i find similar
swithces??

Chanchal

 

[Chanchal]

hi thomas

thanks for that tip. but where should i add @Override? should the
signature of function be

@override public boolean equals(Object obj) ? where can i find similar
switches??

Chanchal

 

[Jean-Francois Briere]

The @Override annotation is not a part of the method signature.
It is just information to the compiler.
It's more like:

@Override
public boolean equals(Object obj)
{
...
}

Take a look at:
http://java.sun.com/docs/books/tutorial/java/javaOO/annotations.html

Regards

 

[Thomas Hawtin]

The @Override annotation is not a part of the method signature.
It is just information to the compiler.
It's more like:

@Override
public boolean equals(Object obj)
{
...
}

For @Override only, some people will write that as:

@Override public boolean equals(Object obj)

Not sure how widespread that is. We still haven't got everyone to put
opening braces at end of line.

http://java.sun.com/docs/books/tutorial/java/javaOO/annotations.html

And the JavaDocs for @Override itself. Annotations are hidden right at
the bottom of the type lists for packages (far bottom left). Note, Java
is case sensitive, so always a capital O.

http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Override.html

Tom Hawtin

 

[Adam Maass]

Here you are overloading the equals method (same name, different
parameter number / type).
You are not overriding it (same name, same parameter number / type).

IE, you need this (or something similar) instead (note that the type of the
parameter is Object, not SaleItem):

public boolean equals(Object other)
{
if(other instanceof SaleItem)
{
SaleItem saleItem = (SaleItem)other;
return this.name.equals(saleItem.name);
}
else
{
return false;
}
}