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Java Forum / General / October 2006argument returning
Hi, if I have a method like this: public static int[][] pass() { int a[][] = {{1,2},{3,4}}; return a; } and than int z[][] = pass(); when I call this method it returns the value of 'a' that is a pointer (reference) to the matrix created. So in the caller z has that value. But I have a doubt, when the method return the variable 'a' is garbaged and thus also its value so how is possible that z has that value? May be because the method returns to 'z' a copy of the 'a' value like any variable value? In the c/c++ when I return a matrix or a pointer in the function that variable must be set as static otherwise it loose its value... Is that wrong? Thanks Hi, What you get is a copy of a. The method has 'a' declared as a local variable, and it is method-scoped. Variable z[][] will be {{1,2},{3.4}} till you explicitly change it. -cheers, Manish Manish Pandit ha scritto: > Hi, > > What you get is a copy of a. that it is a reference that point to that matrix values ... >The method has 'a' declared as a local > variable, and it is method-scoped. so when it returns a is garbaged ... > Variable z[][] will be {{1,2},{3.4}} > till you explicitly change it. because it now point to the reference copy pointed by 'a' ... Correct interpretation? > Manish Pandit ha scritto: > [quoted text clipped - 3 lines] > > that it is a reference that point to that matrix values ... Yes, you get a copy of the reference to object. There is still only one object. >>The method has 'a' declared as a local >> variable, and it is method-scoped. > > so when it returns a is garbaged ... "a" is not garbage collected. It is a variable (a name) and it goes out of scope at the end of the method. This gives rise to the possibility that whatever it was pointing to may become inaccessible (and hence eligible for garbage collection), but the matrix will not be eligible for collection because there is still a live reference to it. The garbage collector will reclaim eligible objects at its discretion later. >> Variable z[][] will be {{1,2},{3.4}} >> till you explicitly change it. > > because it now point to the reference copy pointed by 'a' ... z points to the same (identity) object that a pointed to. > Correct interpretation? Better. Matt Humphrey matth@ivizNOSPAM.com http://www.iviz.com/ Matt Humphrey ha scritto: > "a" is not garbage collected. It is a variable (a name) and it goes out of > scope at the end of the method. This gives rise to the possibility that > whatever it was pointing to may become inaccessible (and hence eligible for > garbage collection), but the matrix will not be eligible for collection > because there is still a live reference to it. The garbage collector will > reclaim eligible objects at its discretion later. so only objects when have not more reference to them will be garbaged and not the variables in which there are their references. > Matt Humphrey ha scritto: > [quoted text clipped - 10 lines] > so only objects when have not more reference to them will be garbaged > and not the variables in which there are their references. I think you've got it--it's a matter of distinguishing between the variable, the reference and the object. Variables hold references to objects and as long as the variable is in scope, the object can be reached. When the variable goes out of scope the reference it was holding disappears but the object still stays. The object will only be eligible for garbage collection when it can no longer be reached from any point in the program. I find pictures helpful for this-- http://www.iviz.com/memory%20pointer.gif A variable going out of scope is the same as having its box (on the diagram) disappear. It doesn't change the objects at all, but if there are no longer any arrows to objects, that object is eligible for garbage collection. Cheers, Matt Humphrey matth@ivizNOSPAM.com http://www.iviz.com/ Matt Humphrey ha scritto: > I think you've got it--it's a matter of distinguishing between the variable, > the reference and the object. Variables hold references to objects and as > long as the variable is in scope, the object can be reached. When the > variable goes out of scope the reference it was holding disappears but the > object still stays. The object will only be eligible for garbage collection > when it can no longer be reached from any point in the program. Thanks the answer has been very clear Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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