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john hunts que no13

anu k
Greenhorn

Joined: Sep 18, 2001
Posts: 2
Q. 13
Which of the following return true?
A."john" == "john"
B."john".equals("john")
C."john" = "john"
D."john".equals(new Button("john"))
Select all correct answers.
answer:A
i answered A, B,D.Can anyone verify me
Thanks
leena rane
Ranch Hand

Joined: Aug 13, 2001
Posts: 280
I feel it is a,b
Jane Griscti
Ranch Hand

Joined: Aug 30, 2000
Posts: 3141
Hi Anu,
The best way to test the results is to write some code and try it

And the answer is:

------------------
Jane Griscti
Sun Certified Programmer for the Java� 2 Platform


Jane Griscti
SCJP, Co-author Mike Meyers' Java 2 Certification Passport
Prakash Yamuna
Greenhorn

Joined: Sep 30, 2001
Posts: 5
--------------------------------------------------------------------------------
The anwsers are A,B for the following reason.
1. The string literal "john" is interned and a single instance is maintained so the expression
"john" == "john" both refer to the same object and hence it returns true.
2. I will skip this since it is obvious
3. The third statement won't compile. You can't assign a value to a String literal
4. In the fourth case you are comparing a String object with a Button object and hence will return false.
Actually the reason it returns false is the way the equals method is usually coded. (This is a recommended practice if you are provide your own equals method for a class)
Ex:
... class String {
public boolean equals(Object o) {
if ( o == null ) {
return false;
} else if ( !(o instanceof String)) {
return false;
} else {
// do the actual value comparison
}
}
Take a look at java.lang.String to get a better idea...

anu k
Greenhorn

Joined: Sep 18, 2001
Posts: 2
thanks leena,jane and prakash..it is clear now
Jane Griscti
Ranch Hand

Joined: Aug 30, 2000
Posts: 3141
anu k,
Please read the JavaRanch Name Policy and re-register using a name that complies with the rules.
Thanks for your cooperation.
------------------
Jane Griscti
Sun Certified Programmer for the Java� 2 Platform
 
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