Can someone tell me why these two strings are not equal?

Question

I got a question similar to this right on a challenge, but only because false has one letter more than true. Initializing identical strings with the new keyword or with a String literal returns false when you compare s1==s2. Both strings have the same length attribute and appear identical when printed. What makes them not equal?
https://code.sololearn.com/cRD5j1mwKxYj/?ref=app

Answer 1

Strings go inside somthing called the "String pool" if you have 2 strings created which are the same, java will store the refrenece to an existing one in that variable.

String str1 = "hello";
String str2 = "hello";

str1==str2 //true both share the same refrenece

Is the same as

String str1 = "hello";
String str2 = str1;

str1==str2 //true

str2 refers to the same refrenece as str1.

If you wanted str1 and str2 to refer to separate instances then you need to use the "new" keyword.

String str1 = new String( "hello");
String str2 = new String(str1);

str1==str2 // false

with objects use == to compare references and str.equals() to compare there values

Answer 2

Anton Böhler thanks for the .equals method! I will certainly remember it now!

Answer 3

Strings aren't compared with '==' because the variable holding the String actually stores a pointer to the String. so with '==' you compare the pointers!
to check for equality of two String use String.equals(String str)
example:

String s1 = "no";
String s2 = "no";
if(s1 != s2){
System.out.println("those are two diffrent Objects!");
}
if(s1.equals(s2)){
System.out.println("the two Strings have the same value!");
}

Answer 4

zemiak thanks. That definitely shows what's under the covers. So why do s2 and s3 (the strings declared literally) have the same pointer?

Answer 5

D_Stark you answered my follow-up to zemiak perfectly. Thanks.

Answer 6

devanille I also integrated those code snippets back into my original code to check things out. Thanks for the credit in the comments.

Writing code is definitely the best teacher! Cheers.

Answer 7

David Crowley Thanks buddy 😊, also good thing to know if your learning, is that objects types like String are treated differently then primitive types like int,double, char ect.. for example

int x = 10;
int y = 20;

As these are not objects you can compare using x==y because primitive type dont have refrenece like objects do, they store the actual value so behind the scenes it looks like 10==20 👍

Answer 8

try add this
System.out.printf( "s1 %s\ns2 %s\ns3 %s\n",
System.identityHashCode(s1),
System.identityHashCode(s2),
System.identityHashCode(s3) );

Answer 9

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Answer 12

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Answer 17

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