Garbage Collections Questions

• Java garbage collection: At which program point is the Bar object created on line 6 eligible for collection? class Bar { } class Test { Bar doBar() { Bar b = new Bar(); // line 6 return b; // line 7 } public static void main (String args[]) { Test t = new Test(); // line 11 Bar newBar = t.doBar(); // line 12 System.out.println("newBar"); newBar = new Bar(); // line 14 System.out.println("finishing"); // line 15 } }
• Java reachability: When is the B object (created on line 3) definitely eligible for garbage collection? void start() { A a = new A(); B b = new B(); // line 3 a.s(b); b = null; // line 5 a = null; // line 6 System.out.println("start completed"); // line 7 }
• In Java memory management, who can actually destroy an object reference x?
• Java GC and parameter passing: When is the Demo object created in start() eligible for garbage collection? class Test { private Demo d; void start() { d = new Demo(); this.takeDemo(d); // line 7 } // line 8 void takeDemo(Demo demo) { demo = null; demo = new Demo(); } }
• After the assignment on line 8, how many X objects are eligible for garbage collection? public class X { public static void main(String [] args) { X x = new X(); X x2 = m1(x); // line 6 X x4 = new X(); x2 = x4; // line 8 doComplexStuff(); } static X m1(X mx) { mx = new X(); return mx; } }
• After line 11 executes, how many X2 objects are eligible for garbage collection (note the cyclic references)? class X2 { public X2 x; public static void main(String [] args) { X2 x2 = new X2(); // line 6 X2 x3 = new X2(); // line 7 x2.x = x3; x3.x = x2; x2 = new X2(); x3 = x2; // line 11 doComplexStuff(); } }
• In the following method, where is there the highest likelihood of the garbage collector being invoked (consider object reachability within methodA)? class HappyGarbage01 { public static void main(String args[]) { HappyGarbage01 h = new HappyGarbage01(); h.methodA(); // line 6 } Object methodA() { Object obj1 = new Object(); // line 9 Object[] obj2 = new Object[1]; // line 10 obj2[0] = obj1; // line 11 obj1 = null; // line 12 return obj2[0]; // line 13 } }
• When does the Float object created on line 3 become eligible for garbage collection? public Object m() { Object o = new Float(3.14F); Object[] oa = new Object[1]; oa[0] = o; // line 5 o = null; // line 6 oa[0] = null; // line 7 return o; // line 8 }