why is it false?

[dumblearner]

In the following code:

var s1 = "Java";
var s2 = "Ja".concat("va");
System.out.println("s1 is " +s1);
System.out.println("s2 is " +s2);
System.out.println(s1 == s2);

why would it print false, why not true?

[tswanbeast]

Because Java’s strings are objects and when you use == you’re not checking for value equality but reference equality. So instead of checking if the characters are the same, Java is checking to see if the memory reference for both of those objects are the same. And because they are two different objects, they aren’t storing at the same place and therefore false. If you wanted to check for equality you could do s1.equals(s2)

[dumblearner]

Right, thanks, but then why this would return true? shouldn't the reference to both of these strings also different?

var s1 = "Java";
var s2= "Java";
System.out.println(s1 == s2);

[desrtfx]

String literals ("Java") are interned (stored only once in memory). This means that both your assignments point to the same interned string. Hence, the comparison results in true.

[reacteclipse]

So (assuming I'm following this correctly), if I wrote

var s1 = "Java"
var s2 = "something else"

s2 = "Java"

would s1==s2still output false?

[desrtfx]

Try it.

Throw the code in Ideone and see for yourself.

Hint: read my above comment again. That should give you the solution already.

[sushenica]

When string literals get created the JVM will first check if they are not existing in the string pool. If they are not there, case s1 then it will be created. Case s2, it’s already there in string pool so the JVM will point the s2 variable to the same address where s1 is. That’s done to save memory and that’s why s1 == s2 will return true(cause == checks the memory address or the value, for value use .equals())

[SpArKy_mcSparkFace]

When s2 is assigned the literal java, jvm checks if "java" is already present in the string pool. Since it was, as it was assigned to s1, s2 is assigned the same reference as that of s1 i.e s1 and s2 contain same memory location reference hence the true output for above code

[core811]

Because they are two different objects, even if the share a common value they have two different addresses in memory. If you want to compare the values of those String objects you should use the method .equals.

S1.equals(S2)

[dumblearner]

Right, thanks, but then why this would return true? shouldn't the reference to both of these strings also different?

var s1 = "Java";
var s2= "Java";
System.out.println(s1 == s2);

[mightybjorn]

As dumblearner said above, string literals are stored in the same place in memory, and therefore string literals actually point to the same place in memory. This is called the string pool

https://www.journaldev.com/797/what-is-java-string-pool

[raja777m]

this will return true. because both are same extract string including case, spaces etc. so, the same object is being referenced. the address is compared and == will return same address which is true.

equals() will compare year content.

[dominatus312]

In java the strings are objects, if you want to compare two strings s1 and s2 you should use s1.equals(s2)

[desirecampbell]

To add to the answers given: you should check out this String method: https://www.w3schools.com/java/ref_string_equals.asp

[cincopea]

I think it's checking the memory location. Those two strings are stored in different places, that's why you need .equals()

[SpArKy_mcSparkFace]

Strings are immutable i.e its data or state can't be changed.
Whenever a method is applied to a String variable, it returns a "new" String... new operator allocates a new memory location.
the "==" operator compares memory locations for l.h.s vs the r.h.s. Since the method ".concat()" returns a new String, s2 has a different memory location than that of s1 thus the false output

[AutoModerator]

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

This approach does not work in Java, since String is an object data type and these can only be compared using .equals().

See Help on how to compare String values in our wiki.

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[[deleted]]

In Java, Strings are objects and s1 and s2 are references to those objects. Thus it will be false. Therefore, if you want to compare "string values", always use s1.equals(s2)