What is the correct answer to this quiz question?

Question

public class A {
String a1;
public A (String a1){
this.a1 = a1;
}
}
class MyClass {
public static void main (String [] arguments){
A a = new A ("1");
A c = a;
a.a1 = new String ("3");
System.out.print (a.a1);
System.out.print (c.a1);
}
}

Answer 1

public class A {
String a1;
public A (String a1){
this.a1 = a1;
}
}
class MyClass {
public static void main (String [] arguments){
A a = new A ("1");
A c = a;
a.a1 = new String ("3");
System.out.print (a.a1);
System.out.print (c.a1);
}
}

Answer: 33

The other one:

public class A {
String a1;
public A (String a1){
this.a1 = a1;
}
}
class MyClass {
public static void main (String [] arguments){
A a = new A ("1");
A c = a;
a = new A("3");
System.out.print (a.a1);
System.out.print (c.a1);
}
}

Answer: 31

Answer 2

but sometimes it says the answer is 31

Answer 3

how so?

Answer 4

33

Answer 5

thanks qwerty

Answer 6

@Yerucham That's a different challenge question. In this one it's "a.a1 = new String("3");" and the other one is "a = new A("3");".

Answer 7

the reason is when A c = a, it makes c as a reference to a. so if you ask for c.a1 it returns the value in the reference. object c will have its own a1 value if you initialize it to the original class like A c = new A("1");
for example the following code as well, will return 31.

public class A {
String a1;
public A (String a1){
this.a1 = a1;
}
}
class MyClass {
public static void main (String [] arguments){
A a = new A ("1");
A c = new A("1");
a.a1 = new String ("3");
System.out.print (a.a1);
System.out.print (c.a1);
}
}

Answer 8

33