Tell me the output?

[Manoj Mani]

class MyClass
{
static int maxElements;

MyClass(int maxElements)
{
this.maxElements = maxElements;
}

}

public class Q19
{
public static void main(String[] args)
{

MyClass a = new MyClass(100);
MyClass b = new MyClass(100);

if(a.equals(b))
System.out.println("Objects have the same values");
else
System.out.println("Objects have different values");
}
}


equals() method was not overrided but still it compiles fine.Why?

[Chandra Bhatt]

Hi Manoj,


Every class inherits Object class so as your class "MyClass" does; You class inherits Object(daddy of all classes) class's equals() method whose definition is as following:


public boolean equals(Object o) {
return this==o;
}

So when you do like
if(a.equals(b)) {
}
a and b are objects of MyClass, so where Object is required as Argument any object of Java can fit there.


Regards,
cmbhatt

[Manoj Mani]

ok thanks.........

[Srinivas Kalvala]

Hello,

It compiles fine and gives the print in else part. The parent class for all classes in java is java.lang.Object class got default implementation for equals method.

 
 /**
     * Indicates whether some other object is "equal to" this one.
     * <p>
     * The <code>equals</code> method implements an equivalence relation
     * on non-null object references:
     * <ul>
     * <li>It is <i>reflexive</i>: for any non-null reference value
     *     <code>x</code>, <code>x.equals(x)</code> should return
     *     <code>true</code>.
     * <li>It is <i>symmetric</i>: for any non-null reference values
     *     <code>x</code> and <code>y</code>, <code>x.equals(y)</code>
     *     should return <code>true</code> if and only if
     *     <code>y.equals(x)</code> returns <code>true</code>.
     * <li>It is <i>transitive</i>: for any non-null reference values
     *     <code>x</code>, <code>y</code>, and <code>z</code>, if
     *     <code>x.equals(y)</code> returns <code>true</code> and
     *     <code>y.equals(z)</code> returns <code>true</code>, then
     *     <code>x.equals(z)</code> should return <code>true</code>.
     * <li>It is <i>consistent</i>: for any non-null reference values
     *     <code>x</code> and <code>y</code>, multiple invocations of
     *     <tt>x.equals(y)</tt> consistently return <code>true</code>
     *     or consistently return <code>false</code>, provided no
     *     information used in <code>equals</code> comparisons on the
     *     objects is modified.
     * <li>For any non-null reference value <code>x</code>,
     *     <code>x.equals(null)</code> should return <code>false</code>.
     * </ul>
     * <p>
     * The <tt>equals</tt> method for class <code>Object</code> implements 
     * the most discriminating possible equivalence relation on objects; 
     * that is, for any non-null reference values <code>x</code> and
     * <code>y</code>, this method returns <code>true</code> if and only
     * if <code>x</code> and <code>y</code> refer to the same object
     * (<code>x == y</code> has the value <code>true</code> :wink: .
     * <p>
     * Note that it is generally necessary to override the <tt>hashCode</tt>
     * method whenever this method is overridden, so as to maintain the
     * general contract for the <tt>hashCode</tt> method, which states
     * that equal objects must have equal hash codes. 
     *
     * @param   obj   the reference object with which to compare.
     * @return  <code>true</code> if this object is the same as the obj
     *          argument; <code>false</code> otherwise.
     * @see     #hashCode()
     * @see     java.util.Hashtable
     */
[B]
    public boolean equals(Object obj) {
return (this == obj);
    }
[/B]