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What is resurrection (in garbage collection)?

An object that has been eligible for garbage collection may stop being eligible and return to normal life. Within a finalize() method, you can assign this to a reference variable and prevent that object's collection, an act many developers call resurrection.

The finalize() method is never called more than once by the JVM for any given object. The JVM will not invoke finalize() method again after resurrection (as the finalize() method already ran for that object). For example,

class Obj {
protected void finalize(){
System.out.println("finalize invoked");
System.out.println("resurrect this object");
Program.objRef = this; //resurrection
}
}

public class Program {
static Obj objRef = null;
public static void main(String args[]) {
objRef = new Obj();
for(int i=0;i<2;i++){
method(i);
System.out.println("objRef = " + objRef);
}
}
static void method(int i) {
System.out.println("Round :"+(i+1));
objRef = null;
System.out.println("Set objRef to " + objRef);
System.gc();//suggest to run the gc
}
}

The output is

Round :1
Set objRef to null
finalize invoked
resurrect this object
objRef = com.xyzws.scjp.Obj@1372a1a
Round :2
Set objRef to null
objRef = null

Developers typically use resurrection to maintain a pool of commonly used objects. However, resurrection can obscure source code and confuse what that code tries to accomplish.


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