Garbage Collections Questions

• At what point is the Bar object, created on line 6, eligible for garbage 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 */ } }
• When is the B object, created in line 3, eligible for garbage collection? void start() { A a = new A(); B b = new B(); a.s(b); b = null; /* Line 5 */ a = null; /* Line 6 */ System.out.println("start completed"); /* Line 7 */ }
• What allows the programmer to destroy an object x?
• When is the Demo object 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 line 8 runs. how many 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 runs, how many objects are eligible for garbage collection? 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(); } }
• Where will be the most chance of the garbage collector being invoked? class HappyGarbage01 { public static void main(String args[]) { HappyGarbage01 h = new HappyGarbage01(); h.methodA(); /* Line 6 */ } Object methodA() { Object obj1 = new Object(); Object [] obj2 = new Object[1]; obj2[0] = obj1; obj1 = null; return obj2[0]; } }
• When is the Float object, created in line 3, eligible for garbage collection? public Object m() { Object o = new Float(3.14F); Object [] oa = new Object[l]; oa[0] = o; /* Line 5 */ o = null; /* Line 6 */ oa[0] = null; /* Line 7 */ return o; /* Line 8 */ }