CODEWITHSUNDEEP
javastringreference
Robin
Robin

Reputation: 179

How is String a reference type in Java?

I understand that classes are reference types, for example I created the following class:

class Class {

String s = "Hello";

public void change() {
    s = "Bye";
} }

With the following code, I understand that Class is a reference type:

Class c1 = new Class(); 
Class c2 = c1; //now has the same reference as c1

System.out.println(c1.s); //prints Hello
System.out.println(c2.s); //prints Hello

c2.change(); //changes s to Bye

System.out.println(c1.s); //prints Bye
System.out.println(c2.s); //prints Bye

Now I want to do the same thing with a String, that doesn't work. What am I doing wrong here?:

String s1 = "Hello";
String s2 = s1; //now has the same reference as s1 right?

System.out.println(s1); //prints Hello
System.out.println(s2); //prints Hello

s2 = "Bye"; //now changes s2 (so s1 as well because of the same reference?) to Bye

System.out.println(s1); //prints Hello (why isn't it changed to Bye?)
System.out.println(s2); //prints Bye

Upvotes: 12

Views: 6859

Answers (5)

Paweł Jarosiewicz
Paweł Jarosiewicz

Reputation: 1

Java is pass-by-value. If you are passing an object into method then you are accualy passing only value of this object, not the object itself and it's value remains the same

Upvotes: -2

Aman Chhabra
Aman Chhabra

Reputation: 3894

This is because you are updating the reference of s2 and not s1. Lets see how your code got executed:

String s1 = "Hello";
String s2 = s1;

A Hello literal string created in String pool, whose reference was then put to s1. Then in the second line s2 also got the same reference.

enter image description here

By now, s1 and s2 are pointing to the same literal string in String pool.

Now when the below piece of code got executed.

Another, literal Bye got created in String pool and the reference was put in s2. Howoever, s1 still has the old reference and hence is printing Hello.

![enter image description here

Upvotes: 7

Loris Securo
Loris Securo

Reputation: 7638

In the first case you are calling a method to the referenced object, thus the referenced object changes, not the 2 references:

method

In the second case you are assigning a new object to the reference itself, which is then pointing to that new object:

new object

Upvotes: 22

Hammad Tufail
Hammad Tufail

Reputation: 1

String s1="Hello"; String s2=s1;

When you do the change like,

s2="Bye";

you are doing this

s2 = new String("Bye");

explicitly.

Upvotes: -3

Thiyagu
Thiyagu

Reputation: 17890

s2 = "Bye";

This is equivalent to creating a new String object and assigning its reference to s2 (s2 = new String("Bye");) and hence s1 and s2 are different.

You are comparing the above with a method call like c2.change() which changes some internal field value.

In other words, s2 = "Bye"; is equivalent to Class c2 = new Class(); in your example. After c1.change(), you cannot expect, c1 and c2 to have the same value for field s.

Upvotes: 0

Related Questions