Java - Comparing Strings

BlackWizard

/*
Below is what im stuck on.
******
String semiColon = ";";

if (tempString2 == semiColon )
{
System.out.print("test");
tempString2 = " ";
}
******

In my mind it should compare the tempString2 with a ;. If it finds
that it is the same as a ; then it should set tempString to a blank
space. I want it to do this so that it knows if its a double figure
or if its a single figure.

EDITED: Solved.

Karoma

I'm a little busy, but what jumps out is that you're comparing Strings using == ...

http://java.sun.com/j2se/1.3/docs/api/java/lang/String.html#equals(java.lang.Object)
&
http://javaalmanac.com/egs/java.lang/CompareStr.html?l=rel

pH

EDIT : What he said

Basq

I always use String.equalsIgnoreCase myself!

The Corinthian

Have you tried the following?

if (tempString2.equals(semiColon) )

Edit: or any of the other above suggestions...

BlackWizard

Oh bugger your right.

I just copied that compare statement from sudo code we made up a few
days ago and totally messed myself up.

heh! Thanks guys! I hadnt got much time to look into it either thats why I
posted it here.

rsynnott

basquille wrote:

I always use String.equalsIgnoreCase myself!

WASTEFUL, in this case. Tsk.

JackKelly

Why is it that some types can only use "==" and others .equals(...)?

The_Bullman

TimAy wrote:

Why is it that some types can only use "==" and others .equals(...)?

I think you can only use the "==" for comparing primitave types. For other classes the equals method should be used

I think..

Hobbes

The_Bullman wrote:

I think you can only use the "==" for comparing primitave types. For other classes the equals method should be used

I think..

Correct. A string is an object not a primative.

garrethg

TimAy wrote:

Why is it that some types can only use "==" and others .equals(...)?

The comparison operator is used to test for equality between both primatives and references to objects.

e.g.

String x= new String("some text");
String y= new String("some text");
String z= x;

/* a is false, it's a comparison between an object and a primative. */
boolean a= x == "some text";
/* b is true, it's a comparison between the primative value of an object field, returned by the method "equals", and a primative. */
boolean b= x.equals("some text");
/* c is false, it's a comparison between references to different objects.*/
boolean c= x == y;
/* d is true, it's a comparison between references to the same object. */
boolean d= x == z;

rsynnott

garrethg wrote:

/* b is true, it's a comparison between the primative value of an object field, returned by the method "equals", and a primative. */
boolean b= x.equals("some text");

Eh? Equals returns a boolean, obtained by comparing the contents of x to the string literal "some text", through a mechanism which, I believe, is implementation-defined. (But in practice almost certainly simply involves comparing two arrays of characters).

Hobbes

garrethg wrote:

/* c is false, it's a comparison between references to different objects.*/
boolean c= x == y;

Thats guaranteed in this case because you have created two new objects but if you did something like

String x= "some text";
String y= "some text";

then x == y could return true, because of how Java handles strings it sees both strings as one object.

[edit]
Just to add. You shouldn't be creating your strings like...

String x = new String("some text");

As this is wasteful because you are creating two objects.

garrethg

rsynnott wrote:

Eh? Equals returns a boolean, obtained by comparing the contents of x to the string literal "some text", through a mechanism which, I believe, is implementation-defined. (But in practice almost certainly simply involves comparing two arrays of characters).

Thanks, I don't know what I (wasn't) thinking at the time

rsynnott

Hobbes wrote:

Just to add. You shouldn't be creating your strings like...

String x = new String("some text");

As this is wasteful because you are creating two objects.

AFAIR, modern Javas optimise this, treating String x as a reference.

Hobbes

rsynnott wrote:

AFAIR, modern Javas optimise this, treating String x as a reference.

well it would be a reference but it would also create a reference for "some text" within the method.

As you said they may do away with this, but its still messy imho.