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test two strings for equality

Posted on 2004-07-30
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Last Modified: 2010-03-31
what is the best way to see if two strings are exactly the same in java? its for when people enter a password into a form twice, i want to check to see that they entered the same password string both times.

thanks!
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Question by:ew0kian
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12 Comments
 
LVL 92

Accepted Solution

by:
objects earned 1000 total points
ID: 11682117
if (s1.equals(s2))
{
  // equal
}
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LVL 3

Expert Comment

by:JavaInTheMorning
ID: 11682306
Since it's a password, the best thing is to use objects' suggestion.
But there is another possibility for other cases:
if (s1.equalsIgnoreCase(s2))
{
   // equal - case insensitive
}
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LVL 37

Expert Comment

by:zzynx
ID: 11683165
Use equals indeed and certainly not ==
Illustration:

        StringBuffer buf1 = new StringBuffer("Hello");
        StringBuffer buf2 = new StringBuffer("Hello");

        if (buf1.toString()==buf2.toString())
            System.out.println("1) equal");
        else
            System.out.println("1) not equal");  // <<<<<<< This is printed (wrong)

        if ( buf1.toString().equals(buf2.toString()) )

            System.out.println("2) equal");      // <<<<<<<< This is printed (correct)
        else
            System.out.println("2) not equal");
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LVL 7

Expert Comment

by:JugglerW
ID: 11683217
Just to be complete: :-)

If you do this:

String pw1 = "Hallo".intern();
String pw2 = "Hallo".intern();

if ( pw1 == pw2 )
  System.out.println( "Equal" );
else
  System.out.println( "Not Equal" );

If you use intern() on both strings of a compare you can use == instead of equals().
But because intern() costs more than an equal it pays only if you do the compare very often.
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LVL 13

Expert Comment

by:Webstorm
ID: 11684066
Hi ew0kian,

If you're using a javax.swing JPasswordField to enter the passwords, you'll get a char[], not a string, which for security reason you can clear after use. If you want to compare 2 char[], use java.util.Arrays.equals(char_array1,char_array2).
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LVL 1

Expert Comment

by:lowenbrausat
ID: 11686865
In case you are NOT using JPasswordField you can use the hashCode() method from String class.

String.hashCode() returns a hash code for the string. The hash code for a String object is computed as  
s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1] using int arithmetic, where s[i] is the ith character of the string, n is the length of the string, and ^ indicates exponentiation. (The hash value of the empty string is zero.)

Examples:

    int hash1 = "Hello".hashCode();
    int hash2 = "Hello".hashCode();
    System.out.println("Hash1 equals to Hash2? "+(hash1 == hash2)); //The result is TRUE

    int hash1 = "Hello".hashCode();
    int hash2 = "HellO".hashCode(); //Note the upper case 'O'
    System.out.println("Hash1 equals to Hash2? "+(hash1 == hash2)); //The result is FALSE


String.hashCode() is case-sensitive. This is the best way - and surest -  to do it.

Hope this can help you!!
c u arround! bye!!
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LVL 7

Expert Comment

by:JugglerW
ID: 11686906
> String.hashCode() is case-sensitive. This is the best way - and surest -  to do it.

Why should this be better or surer than using equals() ???

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LVL 92

Expert Comment

by:objects
ID: 11687024
> Why should this be better or surer than using equals() ???

its not
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LVL 3

Expert Comment

by:JohnnyAffa
ID: 11687225
agrees with objects.......
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LVL 30

Expert Comment

by:Mayank S
ID: 11687611
>> if (s1.equalsIgnoreCase(s2))

Since its a password, I'd prefer to do a case-sensitive comparision, rather than case-insensitive.
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