difference between == and equal() in sting

[subash ecm]

difference between == and equal() in sting

[Amit Vinod Dali]

String str1 = "subash";
String str2 = "ecm";
String combStr = str1 + str2;
String str3 = "subashecm";
System.out.println("combStr.equals(str3)? " + combStr.equals(str3));
System.out.println("combStr == str3? " + (combStr == str3));
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String's “equals()” compares the contents of the two Strings (i.e. the same sequence of characters). “==” is a fundamental operator which verifies whether two references are the same( i.e. whether references refer to same object)

[Nicola Garofalo]

s1 == s2: are s1 and s2 referencing the same String object?

s1.equals(s2): is the content of the String object referenced by s1 the same as the content of the String object referenced by s2 ?

Now, if you want, try this code:

public class TestString{


  public static void main(String[] args){
    String s1 = "hallo";
    String s2 = "hallo";

    String s3 = new String("hallo");
    String s4 = new String("hallo");
    
    System.out.println("s1 == s2 ? :"+(s1==s2));
    System.out.println("s1.equals(s2) ? :"+(s1.equals(s2)));

    System.out.println("s3 == s4 ? :"+(s3==s4));
    System.out.println("s3.equals(s4) ? :"+(s3.equals(s4)));

  }
}

[saurabh agr]

as i know s1==s2 returns true if both string objects refer to same memory location and s1.equals(s2) returns true if the contents of both string objects are same.

[James Hambrick]

saurabh agr wrote:as i know s1==s2 returns true if both string objects refer to same memory location and s1.equals(s2) returns true if the contents of both string objects are same.

Yes I believe that's true. If s1 and s2 both point to the same object then it is equal using ==
.equals compares the value and tells whether it's equal.

To further clarify s1 points to a spot in memory, that spot has an address kinda like our homes do. So if the address is the same for both s1 and s2 then s1==s2 will return true. In C++ s1 and s2 will be called pointers since they point to an object that's in memory. In Java we don't refer to them as pointers.

[Janeice DelVecchio]

I also agree.

So....

String s1 = "hello";
String s2 = "hello";
// both == and .equals() will return true.... same String in the pool
String s3 = new String("hello");
//s3 will NOT return true when compared with s1 for ==, but WILL return true for .equals()    

This is similar when comparing Objects:

// make believe dogs could be compared :)
Dog d = new Dog(Collie);
Dog e = new Dog(Collie);
Dog f = e;
// e and f refer to the same dog on the heap,
// dog d is identical, but a different dog   

This is why you should never use the == operator when referring to objects... unless you're looking for the same object on the heap.

[marc weber]

Essential reading: Strings Literally

[Timothy Sam]

Hi, I'm trying to collect some questions here in the forums to make a tutorial out for in my blog. I tried to answer your question here in this link.

http://devpinoy.org/blogs/lamia/archive/2010/04/15/the-difference-between-and-equals-when-used-in-strings-for-java.aspx

[Campbell Ritchie]

What you didn't say in your blog is that the behaviour of Strings might vary depending on whether they are compile-time constants or not. It is a long time since I tried it, but you can have two identical Strings and have them return false to the == operator, but if they are made up using only compile-time constants, you might get true from ==. You will have to try it and go through the Java Language specification for more details.