How to compare strings that were created by substring?

Question

I'm wondering why it doesn't work, and why I cant't use the CHAR data type for variables a and b. The point is, how to compare the first and the last digits of number (pr) accordingly such way.

String  a, b;
for (int i=100; i<1000;i++) {
    for (int j=100; j<1000;j++) {
        pr=j*i;
        a = String.valueOf(pr).substring(0, 1);
        b= String.valueOf(pr).substring(4, 5);

        if ((a==b) )  {
            System.out.println(pr);
        }
    }
}

Technically he could cast an int to char as long as it was smaller than 2^15-1 (to get the expected result).... Bad practice, but legal — Brian Roach, Feb 20 '13 at 06:21

score 3 · Accepted Answer · answered Feb 20 '13 at 06:18

3

use equals functions
a.equals(b)

If you want to ignore case then use
a.equalsIgnoreCase(b)

answered Feb 20 '13 at 06:18

asifsid88

4,631
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It is not clear why case matters for numerals? – merlin2011 Feb 20 '13 at 06:20
1

@merlin2011 It's about Objects, not numerals http://stackoverflow.com/questions/7311451/difference-between-equals-and-instanceof – MrLore Feb 20 '13 at 06:21
as he mentioned its a string.. so just to give him idea that something of ignoring case is also possible.. so in future it will help him – asifsid88 Feb 20 '13 at 06:21

score 1 · Answer 2 · answered Feb 20 '13 at 06:22

1

This is not JavaScript to use == for String comparison.

Go for equals method

answered Feb 20 '13 at 06:22

LGAP

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Really? If only if this wasn't a dupe and someone hadn't already posted that over five minutes ago .... – Brian Roach Feb 20 '13 at 06:25

score 1 · Answer 3 · answered Feb 20 '13 at 06:24

In Java, operator == compares object identities, so if there are two objects of type String with the same content, == will return false for them:

String x = new String ("foo");
String y = new String ("bar");
if (x == y)
    System.out.println ("Equal");
else
    System.out.println ("Now equal"); // This will be printed

In order to compare String object by content, not by identity, you need to use equals() method like this:

if (x.equals (y))
    System.out.println ("Equal"); // This will be printed
else
    System.out.println ("Now equal");

Note, that if x is null, then x.equals (y) will throw NullPointerException while x == y will return false if y is not null and true if y is null. To prevent NullPointerException you need to do something like this:

if (x == null && y == null || x != null && x.equals (y))
    System.out.println ("Equal"); // This will be printed
else
    System.out.println ("Now equal");

How to compare strings that were created by substring?

3 Answers3