String a = "test";
String b = a;
a = "wuut";
System.out.println(b);
Prints out test
Shouldn't b hold refence of a, not just take its value?
Doesn't Java work that way with objects and stuff?
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3Search for String Immutability on Google.. You will get so many examplesRohit Jain– Rohit Jain2012-10-05 06:27:28 +00:00Commented Oct 5, 2012 at 6:27
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7 Answers
Shouldn't b hold refence of a, not just take its value?
No. The value of a is a reference. References are a way of getting to objects, not variables. The assignment operator just copies the value of the expression on the right hand side into the variable on the left hand side. That's all it does - it's very simple. There's no pass-by-reference in Java, no variable aliasing etc.
3 Comments
Jaanus
But isn't String object? Or String is special object? When I create my objects, will it work then?
Jon Skeet
@Jaanus: Yes, String is an object. But the value of
a isn't a String object. It's a reference to a String object. All your classes will work in exactly the same way.Jaanus
So String is like singleton ? And it holds like lots of values or smthin? When I have
MyObject a = new MyObject(), and when I create Myobject b = a, then it is reference, and changing a also changes b?When a is created lets say it point to place memory_1 in memory.
When b is assigned to a, then b also points to the same memory_1 location.
Now, when a changes value (and because the String Object is immutable) a new value is created now in memory and now a points in memory_2.
But hey, b still points in memory_1.
PS: Immutability is:
In object-oriented and functional programming, an immutable object is an object whose state cannot be modified after it is created.
3 Comments
Jaanus
Is it same for other objects also?
MaVRoSCy
In java most Objects are not immutable. Examples of immutable objects from the JDK include String and Integer. (not
int which is a primitive data type but Object Integer )Jon Skeet
The behaviour here has nothing to do with immutability. It's a complete red herring. When
a changes value, it changes value. It refers to a different object. There's nothing string-specific about that.String a = test
So a is an Object Reference Variable pointing to a String Literal "test" on the heap.
String b = a;
No b is an Object Reference Variable also pointing to the same String Literal "test" on the heap.
Now,
a = "wuut";
But b is still pointing to the String Literal "test",
so Its b which holds the reference to the Object which was previously also referred by a, and but Not to a.
1 Comment
Kumar Vivek Mitra
@Ya thats what i mean...... cause its obvious that why i made it bold, still if its hard to read...let me edit it
No it doesn't. b assumes the value of a. If a changes later, b doesn't. It's not an alias or anything of that nature.
Comments
String a = "test";
Now a holds a reference to the string "test".
String b = a;
The value of a is copied to b. A is a reference to "test", so now b is a reference to "test" too.
a = "wuut";
Now a is assigned a reference to "wuut". This doesn't affect b, because b doesn't hold a reference to a.
Comments
No. b holds the value of a which is a reference to the string "test". What you're thinking about is if you modified the string that a pointed to that b would also change (something like a.append("wuut");). However it is not possible to change Java string because they are immutable.
Comments
Let's go through this step by step.
String a = "test"- create object"test"and referenceapoint on this object.String b = a- create new referencebpoint to the same object"test"a = "wuut"- reassign referenceato another object, but referencebstill point to objecttest
