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Ans. Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
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Ans. String is immutable in java and stored in String pool. Once it's created it stays in the pool until unless garbage collected, so even though we are done with password it's available in memory for longer duration and there is no way to avoid it. It's a security risk because anyone having access to memory dump can find the password as clear text.
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Ans. The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected.
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Ans. Step 1 - We can create a Registry Class having Map of all created objects as key and References list as value.
Step 2 - Whenever we create an object , we should update the Registry in the constructor to add the new object.
Step 3 - Whenever we assign a new reference to the object , we need to update the entry in Map. Similarly if the reference get's removed ( end of scope etc ), we need to remove the entry of reference from the list.
Step 4 - We can have threaded code to monitor the Map to see if any object looses all it's references and should call the method to destroy object and clean the memory.
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Ans. Garbage Collector wont remove a strong reference.
A soft reference will only get removed if memory is low.
A weak reference will get removed on the next garbage collection cycle.
A phantom reference will be finalized but the memory will not be reclaimed. Can be useful when you want to be notified that an object is about to be collected.
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Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package.
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Ans. Yes, doesn't provide exclusive access as we cannot allocate and deallocate memory exclusively as Java internally manages it. The advantage of this is that it relieves the coder for such tasks and helps protect from many bugs that may get introduced with imperfect coding. Moreover as java garbage collector collects all unclaimed memory or objects, it helps the application from memory leaks.
On the flip side , as coder doesn't have extensive excess to memory , it is upto java to decide on the state for programming construct and data storage and hence may introduce some security risks. For example - Java keeps string literals in string pool and there is no exclusive way to remove it and hence may stay and sensitive data in string pool may introduce security issues. Moreover when we overwrite a value or object for a variable / reference, it is upto java to purge those values and hence it may stay in memory for a while till java decide that it is no longer referenced and hence should be removed and hence makes it vulnerable for inappropriate access.
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LikeDiscussCorrect / Improve disadvantages of garbage collection advantages and disadvantages of java memory management java for security applications java with sensitive data memory management
Which of the following methods are used by Java Garbage Collection Mechanism ?
final
finally
finalize
All of the above
Usually asked only to fresh graduates and less experienced developers.
Q12. What is a daemon thread? Give an Example ?
Ans. These are threads that normally run at a low priority and provide a basic service to a program or programs when activity on a machine is reduced. garbage collector thread is daemon thread.
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What kind of thread is Garbage collection thread ?
Daemon Thread
User Thread
System Thread
Active Thread
Which of following is Daemon Thread ?
Thread Scheduler
Daemon Thread
Both of above
None of above
Q13. Difference between HashMap and WeakHashMap ?
Ans. WeakHashMap uses weak reference for keys, which means if the key object doesn't have any reference then both key/value mapping will become eligible for garbage collection.
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Ans. Garbage collection mechanism frees up the memory that is no longer needed. In languages like C / C++ the deallocation needs to be done explicitly by the programmer and hence any leniency may result in memory leak. Garbage collection in java ensures that all unused memory is reclaimed and hence there are no memory leaks.Moreover it relieves the programmer from the hassle of carefully releasing all memory.
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Ans. Now the reference points to a new object in memory. If that was the only reference for the previous object , it will be marked for garbage collection.
Foe example -
Object obj = new Object();
obj = new Object();
object created in first line will be eligible for garbage collection after line 2 as it looses all it's handlers.
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Ans. Yes , a gc method to explicitly call garbage collection immediately on the object. It will provide better flexibility over application that require optimal usage of memory.
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Which of the following about Garbage collection is false ?
