How many objects will be created for this code?
class Main {
int num;
public static void gacemarks(Main m)
{
m.num += 10;
}
public static void main(String[] args) {
Main m1 = new Main();
Main m2 = m1;
Main m3 = new Main();
m2.num = 60;
gacemarks(m2);
System.out.println(m2);
}
}
The answer is 2. But I got 3. m1 will be created, m2 refers to the same object m3 is created newly and after the call, the m object is generated.
In the context of your code, the only two objects I see being explicitly created are the lines in which the new operator appears:
Main m1 = new Main();
Main m3 = new Main();
Here is a breakdown of which is happening in each line:
Main m1 = new Main(); // create new Main object 'm1'
Main m2 = m1; // assign 'm2' to reference 'm1' (no new object)
Main m3 = new Main(); // create new Main object 'm3'
m2.num = 60; // assign a field in 'm2' (no new object)
gacemarks(m2); // repeatedly increment the 'm2.num' field (no new object)
System.out.println(m2); // print 'm2' (no new object)
num, you are incrementing the field of the object you passed in as a parameter.
gacemarks(m2);, the value is the reference itself, i.e. m is a copy of m2 but they both are just references (similar to pointers in C++) to the same object.The answer is 2
That's right. Let's count together:
m1will be created
Right, that's your object number one.
m2refers to the same object
Right again, no new objects added; the count remains one.
m3is created newly
That's your number two.
and after the call, the
mobject is generated.
There's no m object in the code: when you pass m2 to other methods, no copy is created. Hence the final count remains two.
m is a reference to the object that has been passed so it doesn't refer to a new object.
main invokes it, directly or indirectly.Although there are two Main objects created directly in the code (with new operator) one can argue that System.out.println(m2); creates an additional String object due to toString() being called.
String[] args array created when calling main(). It's hard to tell what the question is really about.
Integer.toHexString(), and then it's concatenated to the other stuff like class name (which may or may not create an object) to create another string.
newstatement (orclone()method, but that's another story) is called.m1andm2refer to oneMainobject.m3refers to anotherMainobject. That's 2Mainobjects total.System.out.println(m2.num)aftergacemarks(m2);. You should get 70 then becausemis a reference to the object that is refered to bym2. (I assume thatSystem.out.println(m2)doesn't show that because you didn't overridetoString()).