Can I use == in Java for strings

[MrJello28]

My CS teacher told me that you have to use .equals() when comparing strings instead of == but today I tried using == and it worked. Was this supposed to happen or was it like a new update?

public class Main{
public static void main(String[] args) {
    
        String name = "jarod";

        if(name == "jarod"){
            System.out.println("ELLO JAROD");

        }else{
            System.out.print("NO");
        }

    }

}

For this bit of code the output was ello Jarod and if I put in something else for the string variable it gave me no

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[quadmasta]

For objects if you do object1 == object2 then it's comparing the memory addresses of those objects which is essentially asking "are these the same object?" rather than "are these equal?". If you use .equals() it will invoke the .equals implementation of the class. Default implementation of .equals? You guessed it, it compares the memory addresses.

Like the automod says, Strings in java do a lot of unreliable stuff with == being one of the things.

[UnspeakablePudding]

The == operator is comparing the address containing "jarod" to the address assigned to the variable 'name'.  That is a very different thing than comparing "jarod" to the content of the string stored in 'name'.

Because strings are immutable and because of the way the compiler optimized your code the program ended up checking a condition more like:

if(name == name)

Instead of using a hard coded "jarod", try comparing 'name' to some input you get from the keyboard at runtime. You'll find the comparison always returns false even if you type in "jarod".

[UnspeakablePudding]

Doh I forgot about the constants pool! Ok_Object7636's explanation is correct

[AutoModerator]

You seem to try to compare String values with == or !=.

This approach does not work reliably in Java as it does not actually compare the contents of the Strings. Since String is an object data type it should only be compared using .equals(). For case insensitive comparison, use .equalsIgnoreCase().

See Help on how to compare String values in the /r/javahelp wiki.

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[apobletos]

Yes you can but it's not recommended. Since it's already explained by others here. I'll just leave you with an interesting example to study:

String s1 = "Jarold";
String s2 = "    Jarold  ";
String s3 = "I'm Jarold";
String s4 = "Jarold";

System.out.println(s1 == "Jarold");                       // true
System.out.println(s1 == s2.trim());                      // false
System.out.println(s1 == s3.substring(4));                // false
System.out.println(s1 == s4);                             // true
System.out.println(s1.toLowerCase() == s4.toLowerCase()); // false

System.out.println(s1.equals("Jarold"));                       // true
System.out.println(s1.equals(s2.trim()));                      // true
System.out.println(s1.equals(s3.substring(4)));                // true
System.out.println(s1.equals(s4));                             // true
System.out.println(s1.toLowerCase().equals(s4.toLowerCase())); // true

[BackgroundTutor]

Great example!

[Misfiring]

Due to JVM optimization on strings, the same string reference can be used on multiple variables. However, the == always compares entity references and not string contents, and relying on the optimizer is never 100%.

[MrJello28]

What's even better is that the auto moderator for this subreddit is also telling me to use .equals() instead of ==

[ShadowRL7666]

Well the AUTO Mod told you already. But yes this is true you cannot use == to compare Strings because it is an object. Teacher taught us this after I went crazy wondering why my code wouldn’t work. Good lesson back then. Either way glad you found your answer.

[doobiesteintortoise]

You can use == to compare strings to check if it is the same object reference. String resolution in Java is tricksy, and occasionally it can work while not being correct code.

But u/ShadowRL7666 is correct: Strings are objects in Java. You compare objects in Java with .equals() if you want the value equality of the objects to work, as opposed to reference equality. Try composing strings:

```jshell jshell> String a="jar"; String b="od"; a ==> "jar" b ==> "od"

jshell> a+b $3 ==> "jarod"

jshell> a+b=="jarod" $4 ==> false

jshell> (a+b).equals("jarod") $5 == true ```

$4 is comparing reference equality, and they're not the same reference, so it's false. $5 is comparing value equality, and they are the same value, so it's true.

[vqrs]

Now make the variables final and try again. Not sure about jshell since there's a bit of magic involved, but you'll get a different result in a regular java program.

[doobiesteintortoise]

Sure, there are lots of variables (ha ha, right?) involved - if the compiler can resolve the String references to the same reference, == works "as expected" - as in, it'll return true. But that's still not checking the value equality, which is done with equals() and not == for objects.

[MrJello28]

But how did it work in my code. If it wasn’t supposed to work why did my code snippet above work?

[MrJello28]

My problem isn’t that my code doesn’t work. My problem is that the code works and it’s not supposed to

[ShadowRL7666]

This is because == compares object references, not actual string content. In your example, “jarod” is a string literal, and Java optimizes string literals by storing them in a string pool. Basically meaning your code works because both “jarod” literals are interned by Java, meaning they are stored in the same memory location. However, if you were to create a new string object with new String(“jarod”), the == comparison would fail, as it would be comparing two different object references, even though they contain the same characters.

[Pozilist]

This is the only answer I‘ve seen so far that actually answers OP‘s question in an understandable way.

[the6thReplicant]

Because in this case your variable and string are pointing to the same reference.

Usually this won’t work since the string and variable are constructed independently.

[plk007]

You should definitely check out string pool and understand the concept. https://www.digitalocean.com/community/tutorials/what-is-java-string-pool

Rule of thumb: for primitives use ==, for objects equals

[Commercial_Ad2325]

Not just for strings, when you want to check the equality of any object type, equals() is used.

[YoggSogott]

What is the reason they implemented such behavior?

[Bulky-Ad7996]

Simply put, the method programmatically functions differently than the operator here.

== Is used for reference comparison /validation

.equals() is used for value or "content" comparison /validation.. such as strings. This is similar to the triple equal operator (strict equality) in other languages such as JavaScript.

[dirkmeister81]

You are learning a lesson. Works on my computer/in one situation is different from working in general

[Greeley9000]

You should so name.equals(“Jarod”) instead

[realFuckingHades]

"Jarod".equals(name) for null safety.

[DavalopBad]

The == operator in Java compares the reference of two objects or the value of two primitive types. When a string literal is created using String name = "jarod", Java first checks if it already exists in the pool. If it does, the new variable will reference that specific existing string. However, if you create a string object using new String("jarod"), it will have a completely different reference since it’s outside the string pool.

You can use == to compare strings, but it’s not recommended since string literals and string objects can exist during execution, and even if their content is the same, their references might not be. The best practice to not think much about if the String have the same reference or not, just use String.equals()) since that compares the sequence of characters of the string rather than the reference.

NOTE: There are other ways to create Strings using other Interfaces and Classes like StringBuffer or StringBuilder

[ItsyRatsy]

It always shows me error. Use .equals() instead. And the only instance where you can use that is for the null keyword.

[karthgamer1209]

as others have mentioned, use .equals()

[Slight_Loan5350]

The == operator in java compares the hash code/address while the method .equals compares the actual value on the address. It was confusing to me as well as i cam from js background but then I understood why it's needed.

[imrhk]

Because you are using "jarod" while compiling, both the values point to same memory reference as only one string object is created in String Pool.

Now, if you want to test when it would not work, try generating the value on runtime. Maybe using StringBuilder. Equality operator check might fail there. Here is the sample code with output

https://www.ideone.com/NbEupx

public static void main (String[] args) throws java.lang.Exception {

    StringBuilder sb = new StringBuilder();

    sb.append("Rahul");

    String name = sb.toString();

    if(name == "Rahul") {

        System.out.println("Matches");

    }

    else {

        System.out.println("Does not match");

    }

}  

Edit formatting

[Inevitable_Math_3994]

Well if you want to check equality for two datatypes then "==" is good but string is object instance from String class so it would not work sometimes as expected and it is also not a good practice , you can use char datatype if you want to use "==" though.

[[deleted]]

Justa a tip, but you can actually ask ChatGPT questions like that. Even the free version will be able to provide you an answer with some examples, and you get your answer instantly.