Doubt in equals()

[Guru dhaasan]

In the following code:
-----------------------
public class eq{
public static void main(String args[]){
obj1 oba=new obj1(1,2);
obj1 obb=new obj1(1,2) ;
if (oba.equals(obb)){System.out.println("oba == obb");}
else {System.out.println("oba!=obb");}
obj2 ob2=new obj2();
if (ob2.equals(oba)) {System.out.println("ob2==oba");}
else {System.out.println("ob2!=oba");}
}
}

class obj1{
private int x=0;
private int y=0;
obj1(int x,int y){
this.x=x;
this.y=y;
}
public int getX(){
return this.x;
}
public int getY(){
return this.y;
}
}

class obj2{
private int x=1;
private int y=2;
public boolean equals(Object ob){
obj1 one=(obj1)ob;
if ((one.getX()==x)&&(one.getY()==y)){
return true;
}
else{
return false;
}
}
}

The output is:
oba!=obb
ob2==oba

Why the first output is not equal???
After all, equals method compares bit by bit and both oba and obb has exactly the same contents

Any explanation appreciated.

Thanks
Guru

[Chandra Bhatt]

Hi,

Because for class obj1 you have not overridden the eqauls() method.


Thanks and Regards,
cmbhatt

[lalitha kalanadhbhatla]

Hai Guru,
As you sent the values 1,2 to the constructor of obj1 the values are passed by value.The changes takes place in the class obj1 but the values are not returned to main class as the pass by value only makes a change to copy that is passed to the obj1 but the main class remains unaffected.

[Prasanna Venkatesh]

Hi Guru ,
If your not overriding the equals method , it will just bit compare the object referecenes. So in the first case obviuosly it wont be equal , since they are reffering different object .
If you add some thing like this
obj1 obc= obb;
then always
if ( obb.equals(obc) )
{
System.out.println("obb==obc");
}
else
{
System.out.println("obb!=obc");
}

will return true .since they are reffering same objects. Hope this helps

[Chandra Bhatt]

Try this modified code,

public class Demoequals {
 

public static void main(String args[]){
obj1 oba=new obj1(1,2);
obj1 obb=new obj1(1,2) ;
if (oba.equals(obb)){
System.out.println("oba == obb");
}
else {
System.out.println("oba!=obb");
}
obj2 ob2=new obj2();

if (ob2.equals(oba)) {
System.out.println("ob2==oba");
}
else {
System.out.println("ob2!=oba");}
}
}
 
class obj1{
private int x=0;
private int y=0;
obj1(int x,int y){
this.x=x;
this.y=y;
}
 
public boolean equals(Object o) {
//do instanceof test here
return (((obj1)o).x ==x) && (((obj1)o).y ==y);

}
public int getX(){
return this.x;
}
 
public int getY(){
return this.y;
}
}
 

class obj2{
private int x=1;
private int y=2;
public boolean equals(Object ob){
obj1 one=(obj1)ob;
if ((one.getX()==x)&&(one.getY()==y)){
return true;
}
else{
return false;
}
}
}

Thanks and Regards,
cmbhatt

[Arad Chear]

while you not override equal method in obj1 the original method ( in class Object ) will test only throw == operator

so you test two different reference so oba!=obb but its meaningfully equal that doesn't matter if you don't override the equal method

its like this :


if (oba==obb){System.out.println("oba == obb");}
else {System.out.println("oba!=obb");}