Understanding Garbage Collection

Question

Garbase Collector collects any objects that the program cannot access. If an object cannot be accessed, it will be collected by the garbage collector if needed.
Can someone explain with a simple example when an object cannot be garbase collected? preferably an example with 'String'
thanks

Answer 1

String text = "Hallo";
//the instance "Hallo" cannot be collected here
String message = text;
text = null;
//neither here;
message = null;
//The instance "Hallo" can be collecter here by the GBI don't think that this is the way it works. Garbage collection frees memory for use, and in this case, the variable text could still be referenced, even though it does not have a value. I might be wrong, but my guess would be that setting a variable to be null, would result in the location of memory allocated for the variable to be emptied (e.g. C-function memset). If the garbage collection would occur when the variable is set to null might cause problems, like so:
String foo = "bar; // Create and initliaze variable
foo = null; // Set to null, assume garbage collection
String bar = "foor"; // Create and initialize. If this were now stored
// in the same memory slot as foo, which would be possible due
// to the garbage collection, problems would arise from next line
foo = "bar"; // Now foo and bar refer to the same memory locationTherefore garbage collection occurs only when no object or class holds no reference to the variable, example:
if(foobar) {
   String localVar = "local variable";
// When the if-block ends, the variable localVariable is collected
// as it no longer can be referenced.Tuomas Rinta