== and .equals()

Question

Why is the output true?

String a = "hi";
String b = "hi";

System.out.println(a == b);

A String is an object, when using == it compares the memory location.. so how is it true? Does it mean that they point to the same location? So why do we need .equals() if the == works ?

Answer 1

Yahel

Yes.

This tutorial explains it well:
https://www.baeldung.com/java-string-pool

Answer 2

Hello Yahel

If you create a String in this way:
String a = "hi";
Then it is stored in the string pool. If you now create another String "hi" it takes it from the string pool.
So in this case you do not really create a new String.
As far as I know it is the only example where == returns true

String a = "hi";
String b = new String("hi");
a == b returns false

So a "hi" from user input or any other source will normally return false.

Answer 3

Yahel

Because here you are not creating a literal. next() and nextLine() returns a String Object.

Answer 4

Denise Roßberg thanks! Finally I get it :)

Answer 5

Denise Roßberg ohhh, makes sense. Thanks

Answer 6

pool saves memory, by intern() if String is in pool is used, else added and used

String h1 = "hi";
String h2 = new String("hi").intern();

System.out.println( System.identityHashCode(h1) );
System.out.println( System.identityHashCode(h2) ); // returns same number

Answer 7

String h = "h", i = "i";
System.out.println( "hi" == h+i); //false
System.out.println( "hi".equals(h+i) ); //true

Answer 8

zemiak so why does my example output true ?

Answer 9

Denise Roßberg can you elaborate about the "String pool"?
Is it just pointing to the same value? When assigning a String without the "new" keyword, does it just point to an existing value (if there is one), and doesn't create a new one (assigning extra memory for this value)?

Answer 10

Denise Roßberg oh, so why doesn't it output true?

Scanner scan = new Scanner(System.in);
String a = scan.next();
String b = "hi";
System.out.println(a == b);

Answer 11

if you want ensure of use String pool, you can use .intern()

String hi = new String("hi").intern();
System.out.println( "hi" == hi ); //true

Answer 12

zemiak Ok, thanks. I read that there obviously can't be duplicates in the String pool, so what happens if you call the intern function on a String that already exists in the String pool? What is the String variable pointing to ?