— Scott McNealy, Sun Microsystems Chairman, President and ceo

Instance Variable
Local Variable

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266
 
chapter 9
Which of the lines of code on the right, if added 
to the class on the left at point A, would cause 
exactly one additional object to be eligible for the 
Garbage Collector? (Assume that point A (//call 
more methods) will execute for a long time, giving the 
Garbage Collector time to do its stuff.)
Exercise
BE the Garbage Collector
public class GC {
public static GC doStuff() {
GC newGC = new GC();
doStuff2(newGC);
return newGC;
}
public static void main(String [] args) {
GC gc1;
GC gc2 = new GC();
GC gc3 = new GC();
GC gc4 = gc3;
gc1 = doStuff();
// call more methods
}
public static void doStuff2(GC copyGC) {
GC localGC = copyGC;
}
}
File Edit Window Help Sleep
A
1
2
3
4
5
6
7
8
9
copyGC = null; 
gc2 = null;
newGC = gc3; 
gc1 = null;
newGC = null;
gc4 = null; 
gc3 = gc2;
gc1 = gc4;
gc3 = null; 
exercise: 
Be the Garbage Collector

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constructors and 
gc
you are here
4
267
class Bees {
Honey [] beeHA;
}
class Raccoon {
Kit k;
Honey rh;
}
class Kit {
Honey kh;
}
class Bear {
Honey hunny;
}
public class Honey {
public static void main(String [] args) {
Honey honeyPot = new Honey();
Honey [] ha = {honeyPot, honeyPot, honeyPot, honeyPot};
Bees b1 = new Bees();
b1.beeHA = ha;
Bear [] ba = new Bear[5];
for (int x=0; x < 5; x++) {
ba[x] = new Bear();
ba[x].hunny = honeyPot;
}
Kit k = new Kit();
k.kh = honeyPot;
Raccoon r = new Raccoon();
r.rh = honeyPot;
r.k = k;
k = null;
} // end of main
}
Popular 
Objects
In this code example, several new objects are created.
Your challenge is to find the object that is ‘most popular’, 
i.e. the one that has the most reference variables referring 
to it. Then list how many total references there are for 
that object, and what they are! We’ll start by pointing out 
one of the new objects, and its reference variable.
Good Luck !