Impact of methods on instance fields and static variables

Here is the analysis of the code:

• After A a = new A(1);, a.instanceNumber is 1, a.x is 1, and A.y (the static field) is 2.
• The method doIt(z, a) is called with z=3 and a referencing the object with instanceNumber=1.
• Inside doIt, i is a local copy of z (which is 3), so i = 11 does not affect z outside.
• a.x = 12; sets the x of the object a points to, so a.x becomes 12.
• a.y = 13; sets the static field y to 13.
• a = new A(2); creates a new object with instanceNumber=2 and assigns it to local variable a. The original object remains unchanged.
• a.x = 21; and a.y = 22; modify the new object.

After the method call:

• The original object a still points to the first object with instanceNumber=1.
• Its x is 12.
• The static field y is 22.
• The variable z remains 3.
• The new object with instanceNumber=2 is not referenced after doIt.

Therefore:

• a points to the original object with instanceNumber=1.
• a.instanceNumber is 1.
• a.x is 12.
• a.y is 22.
• z is 3.