[Java] Garbage Collection

Garbage Collection

- Garbage Collection is process of reclaiming the runtime unused memory automatically

- It is a way to destroy the unused objects

- Java is performed automatically, Java provides better memory management

1. Advantage

- It makes java memory efficient

- It is automatically done by the garbage collector(a part of JVM)

2. How can an object be unreferenced?

- By nulling the reference

- By assigning a reference to another

- By annoymous object etc

1) By nulling a reference

Employee e = new Employee(); e = null;

2) By assigning a reference to another

Employee e1 = new Employee(); Employee e2 = new Employee(); //now the first object referred by e1 is available for garbage collection e1 = e2;  

3) By annonymous object

new Employee();  

3. finalize() method

- The finalize() is invoked each time before the object is garbage collected

- It can be used to perform cleanup processing

protected void finalize(){}  

1) point

- The garbage collector collects only those objects that are created by new keyword

- If you have created any object without new, you can use finalize method to perform cleanup processing

4. gc() method

- gc() is used to invoke the garbage collector to perform cleanup processing

- gc() is found in System and Runtime classes

public static void gc(){}  

1) point

- Garbage collection is performed by a daemon thread called GC

- This thread calls the finalize() before object is garbage collected