| In the Java programming language, dynamic allocation of objects is achieved using the new operator. An object once created uses some memory and the memory remains allocated till there are references for the use of the object. When there are no references for an object, it is assumed to be no longer needed and the memory occupied by the object can be reclaimed.There is no explicit need to destroy an object as java handles the de-allocation automatically. The technique that accomplishes this is known as Garbage Collection.Programs that do not de-allocate memory can eventually crash when there is no memory left in the system to allocate. These programs are said to have memory leaks. |
In Java,Garbage collection happens automatically during the lifetime of a java program, eliminating the need to de-allocate memory and avoiding memory leaks.In C language, it is the programmer’s responsibility to de-allocate memory allocated dynamically using free() function.
Note : All objects are created in Heap Section of memory. More on this in a later tutorial.
Step 1) Copy the following code into a editor
Step 2) Save, Compile and Run the code. As shown in the diagram , two objects and two reference variables are created.
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| Figure: Object Creation after compiling and executing above code |
Step 3) Uncomment line # 20,21,22. Save , compile & run the code.
Step 4) As show in diagram below, two reference variables are pointing to the same object.
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| Figure: View of objects after performing step 3 |
Step 5) Uncomment line # 23 & 24. Compile , Save & Run the code
Step 6) As show in diagram below , s2 becomes null , but s3 is still pointing to the object and is not eligible for garbage collection.
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| Figure: S2 pointing to null after execution of 23 line |
Step 7) Uncomment line # 25 & 26 . Save , Compile & Run the Code
Step 8) At this point there are no references pointing to the object and becomes eligible for garbage collection. It will be removed from memory and there is no way of retrieving it back.
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| Figure: S2 and S3 becomes eligible for garbage collection |
Garbage Collection Important Points to Note:
1) If you want to make your object eligible for Garbage Collection , assign its reference variable to null.
2) Primitive types are not objects. They cannot be assigned null.
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| Primitive Types can't be set to null |
