Reg == and equals

[Angela Narain]

What is the best way to solve code relating to
use of == operator and equals method
( with both primitive dataTypes,
reference dataTypes specifically String related comparisons )
Is someone having a good example covering all possible
comparisons.
Thanks

[Guoqiao Sun]

Hi, Angela, it is not so easy to give a complete list of all possible comparisons. In my understanding, if some class does not override the equals method, it will find and use the equals method in its super class till Object where equals is defined, where the equals() method does the same thing as ==.
And String, File, Date as well as Boolean, Byte, Short, Character, Integer, Long, Float, Double all override the equals() method. The comparison between two objects of them, the result will be true if the two objects are logically the same.
See the following code for more understanding:

import java.io.File;
import java.util.Date;
public class Test extends Object
{    
    public static void main(String args[])
    {
        Boolean b1 = new Boolean("Java");
        Boolean b2 = new Boolean("avaJ");        
        System.out.println(b1.equals(b2));  //true
        Float f1 = new Float(+0.0);
        Float f2 = new Float(-0.0);
        System.out.println(f1.equals(f2));  //false      
        
        Float f3 = new Float(+0);
        Float f4 = new Float(-0);
        System.out.println(f3.equals(f4));  //true
        Double d1 = new Double(+0.0);
        Double d2 = new Double(-0.0);
        System.out.println(d1.equals(d2));  //false      
        
        Double d3 = new Double(+0);
        Double d4 = new Double(-0);
        System.out.println(d3.equals(d4));  //true
        
        StringBuffer sb1 = new StringBuffer("test");
        StringBuffer sb2 = new StringBuffer("test");        
        System.out.println(sb1.equals(sb2)); //false
        
        File file1 = new File("testfile");
        File file2 = new File("testfile");        
        System.out.println(file1.equals(file2));  //true
        
        Date date1 = new Date("07/09/2001");
        Date date2 = new Date("07/09/2001");        
        System.out.println(date1.equals(date2));   //true
    }
}

Hope it helps,

------------------
Guoqiao Sun
Sun Certified Programmer for Java™ 2 Platform
try my mock exam¹² at my homepage.

[Guoqiao Sun]

Forget to mention that StringBuffer doesn't override the equals method. So the comparison will return false even if the two objects contains the same String inside.
Regards,
------------------
Guoqiao Sun
Sun Certified Programmer for Java™ 2 Platform
try my mock exam¹² at my homepage.

[Anonymous]

I am not sure how much will this be of help to you.... But still
have a look here