StringBuffer and .equals()

this is my test codes:
public class Testing
     public static void main(String arg[])
          StringBuffer sb1 = new StringBuffer("test");
          StringBuffer sb2 = new StringBuffer("test");
          if (sb1.equals(sb2))
               System.out.println("1");
                System.out.println("End");
}At runtime, the program only prints out End, without the number 1.
My question is shouldn't the if-statement is equal to true?
Doesnt .equals() method compare the content of one object to another object?
thanks for any explanation
daffy

String is deliberately immutable (a value object). This means you can pass it around and share it as a data member in many classes without the danger that one class might change its value and therefore surprise all the other classes sharing it. IOW, you can treat it much like a basic type. StringBuffer is class for the efficient manipulation of String contents. It is mutable, and not really intended to be 'passed around' (i.e. made part of a interface, declared as an argument or return type in a non-private method) or shared by classes. In general, a String is passed to a method, manipulated via StringBuffer, then returned as a new String.

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Hi,
In some Java Classes, I saw that
toString()
hashCode()
equals()
these 3 methods of Object Class is overloaded.
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Regards,
S.Prabu

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Now i'm working under hashtable functions. In that all are asking me to overwrite hashCode and equals method. Why?
Please let me know briefly...........

jverd wrote:
euph wrote:
jverd wrote:
euph wrote:
REFTY5_ wrote:
Hi ,
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Please let me know briefly...........Thery're asking you to override the equals and hashCode methods. Override means replace.So does "overwrite." However, as you point out, "override" is the correct word here.So you think "overwrite" means the same as "replace"?To the same extent that "override" does. But both are in the general sense. Override has a specific meaning in this Java context, and overwrite does not.Don't tell me. That's what I said in my original reply.
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Hi all:
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ONE,
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Answered by the test code by myself.
We can use either equals or (==) to see if they are the same value.
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Thanks for your reply
I have one more question.
When equal method of Object class give the same result as equals we override then why should we override equals.For example see the below code
public class EqualsTest{
public EqualsTest() {
super();
public static void main(String[] args) {
Moof one =new Moof(8);
Moof two =new Moof(8);
if(one.equals(two))
System.out.println("one is equals to two");
class Moof {
private int moofvalue;
Moof(int val){
System.out.println("val inside moof constructor"+val);
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System.out.println("moofvalue inside moof constructor" +moofvalue);
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System.out.println("moofvalue inside getmoffvalue method "+moofvalue);
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true
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Thanks in advance

hi javanovice33,
simply put:
== tests if two object references point to the same and only one object
and
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HJava wrote:
Thank you for all the reply,
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            Message was edited by:
ehj3000

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I want to store some data in a list or an Array (but apparently an Array only holds 10 items?) and then I want to be able to check if myString is equal to any of the posts in the array/list.
Or if I use a StringBuffer I want to check to see if myString is part of the StringBuffer?
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I want to store some data in a list or an Array (but
apparently an Array only holds 10 items?)Uh, no. Arrays can (theoretically) contain Integer.MAX_VALUE elements.
and then I want to be able to check if myString is equal to any
of the posts in the array/list.Don't confuse String's equals() method with the equality operator '=='. The == operator checks that two references refer to the same object. If you want to compare the contents of Strings (whether two strings contain the same character sequence), use equals(), e.g. if (str1.equals(str2))...
Example:String s1 = "foo";
String s2 = new String("foo");
System.out.println("s1 == s2: " + (s1 == s2)); // false
System.out.println("s1.equals(s2): " + (s1.equals(s2))); // trueFor more information, check out Comparison operators: equals() versus ==
Or if I use a StringBuffer I want to check to see if
myString is part of the StringBuffer?See above discussion on .equals().
How do I do this?
Here are some other resources to help you get started with Java.
The Java Tutorial - A practical guide for programmers
Essentials, Part 1, Lesson 1: Compiling & Running a Simple Program
New to Java Center
How To Think Like A Computer Scientist
Introduction to Computer Science using Java
The Java Developers Almanac 1.4
JavaRanch: a friendly place for Java greenhorns
jGuru
Bruce Eckel's Thinking in Java
Joshua Bloch's Effective Java
Bert Bates and Kathy Sierra's Head First Java

What is difference between == and equals ??? i wanna know in detain example

Hi
1) String s1 = new String("abs");
          String s2 = s1;
          System.out.println(s1==s2);
          System.out.println(s1.equals(s2));
Output:
true
true
2)
String s1 = new String("abs");
          String s2 = s1;
          s2 = "abs";
          System.out.println(s1==s2);
          System.out.println(s1.equals(s2));
output:
false
true
i m not getting that here s1 is object and its assigned to s2 object so both are point to same memory location...but while assinging s2 = "abs" which is same as s1 then its behave like different object y?

but while assinging s2 = "abs" which is same as s1 then its behave like different object"abs" is "the same as" s1 in the sense that it represents the same characters in the same order. But it is also different from s1 in that it refers to a different object. It's the same distinction as you get comparing two $20 notes: they are equal but, since there are two of them they cannot be identical.
With Java reference variables this equal/indentical distinction is represented by equals()/==.
In general each class defines its own equals(). (Much as there will be a legal definition what what counts as being equal to $20.) This realationship is generally what you mean and hence the rule "when comparing objects use equals()".

Difference between .equals("") and .equals(null)

Can any one please tell me the difference between the following?
String someString;
someString = someMethod(someParameter);
After the method call, if I am going for a check like this..
what will each check do?
1. if (someThing.equals(null))
2. if (someThing.equals(""))
3. if (something == null )
4. if (something == "" )
Thanks in advance,
Regards
Rakesh

First, understand that the empty string ("") and null are two very different things. The empty string ("") is a string object that just doesn't contain any characters. It's still an object though--you can call it's methods.
Null, on the other hand, is essentailly nothing. It's a special value that means "Nothing. No object here." (Ignoring for now the distinction among the null type, a null reference, etc.) You can't call methods or refer to fields on null. If you try, you'll get a NullPointerException.
1. if (someThing.equals(null))Calls the equals method on someThing to compare someThing to null. If someThing is not null, this returns false. If someThing is null it... what? returns true? Nope. Throws NullPointerException. You can't call the equals method on a null someThing.
Therefore there's no point in ever using equals(null).
2. if (someThing.equals(""))Calls the equals method on someThing to compare someThing to the empty string (""). If someThing is not null, but is empty, it returns true. If someThing is non-null and is not empty (e.g., "abc"), it returns false. If someThing is null, it throws NPE.
One generally uses the equals method, not the == operator to compare objects--that is, to see if their contents or states are equal. The == operator is used to see if two referecnes refer to the same object, or if a reference is null.
3. if (something == null ) Evaluates to true if something is null and to false if something is non-null. Never throws NPE (since we're not calling a method or accessing a field).
4. if (something == "" ) You never really want to use == to compare a String variable to a String literal like this. This checks to see if the reference something is referring to the same object as the "" is. The "" will be referring to an object in the constant pool. Even if something is the empty string, it may not refer to the same entry in the constant pool.
That is (something == "") could evaluate to false, but something.equals("") could return true.

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