Doubt in Strings

[Dhivya rajagopal]

public class PatrickString {
  public static void main(String args[])
  {
    String s1 = new String("amit"); 
    System.out.println(s1.replace('m','r')); 
    System.out.println(s1); 
    String s3="arit"; 
    String s4="arit"; 
    String s2 = s1.replace('m','r'); 
    System.out.println(s2);
    System.out.println(s2==s3); 
    System.out.println(s3==s4);
   }
} 

The above program displays the following output:
arit
amit
arit
false
true
My doubt is how the output for s2==s3 becomes false?
can you please explain

[Campbell Ritchie]

Dhivya rajagopal wrote:

public class PatrickString {
  public static void main(String args[])
  {
    String s1 = new String("amit"); 
    System.out.println(s1.replace('m','r')); 
    System.out.println(s1); 
    String s3="arit"; 
    String s4="arit"; 
    String s2 = s1.replace('m','r'); 
    System.out.println(s2);
    System.out.println(s2==s3); 
    System.out.println(s3==s4);
   }
} 

The above program displays the following output:
arit
amit
arit
false
true
My doubt is how the output for s2==s3 becomes false?
can you please explain

Because the == operator does not check whether the two Strings are identical, but whether they are the same object. The compiler and JVM have no way of knowing that the two Strings’ contents are the same, so they are different objects. Try adding .intern() after the replace() call.

[Winston Gutkowski]

Dhivya rajagopal wrote:My doubt is how the output for s2==s3 becomes false?
can you please explain

String is an object. When comparing objects, you should always use equals() unless, as Campbell said, you want to know if two objects are the the same object.

At it's worst (ie, if the object doesn't have its own equals() method) it will do the same thing as '==', but if, like String, it has some other meaning, it will do what you expect; '==' won't.

Winston

[Rajesh Nagaraju]

Can someone please help me understand why the System.out.println values are not coming completely

public class PatrickString {   
  public static void main(String args[])   
  {   
    //String s1 = new String("amit");    Rajesh
    String s1 = "amit";    
    System.out.println(s1.replace('m','r'));    
    //System.out.println(s1);    
    String s3="arit";    
    String s4="arit";    
    String s2 = s1.replace('m','r');    
    String s5 = s1.replace('m','r').intern();    
    System.out.println(s2);   
    System.out.println("s2==s3:"+s2==s3);    
    System.out.println("s3==s4"+s3==s4); 
    System.out.println("s3.intern()==s4.intern()"+s3.intern()==s4.intern()); 
    System.out.println("s2==s5"+s2==s5);    
    System.out.println("s2.intern()==s5.intern()"+s2.intern()==s5.intern());
    System.out.println("s1==s3");
   }   
} 

OutPut:
arit
arit
false
false
false
false
false
s1==s3

[Matthew Brown]

You need to look at this: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html

Check the relative order of precedence of + and ==. Now, what would you expect the result of "s2==s3:"+s2==s3 to be?

[Rajesh Nagaraju]

Matthew Brown wrote:You need to look at this: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html

Check the relative order of precedence of + and ==. Now, what would you expect the result of "s2==s3:"+s2==s3 to be?

Thanks Mathew,

hence "s2==s3:Arit"==s2 will be false

Correct me if I am wrong

[Praveen Kumar M K]

Dhivya rajagopal wrote:

public class PatrickString {
  public static void main(String args[])
  {
    String s1 = new String("amit"); 
    System.out.println(s1.replace('m','r')); 
    System.out.println(s1); 
    String s3="arit"; 
    String s4="arit"; 
    String s2 = s1.replace('m','r'); 
    System.out.println(s2);
    System.out.println(s2==s3); 
    System.out.println(s3==s4);
   }
} 

The above program displays the following output:
arit
amit
arit
false
true
My doubt is how the output for s2==s3 becomes false?
can you please explain

There is another concept here :
The function replace creates a new String instance with value "arit" and returns a reference which you are storing in the variable s2. For s3 and s4 however, 2 different String instances are not created. Its the same string literal which is referenced by 2 variables. You can read up on a concept called String literal pooling.