Week 25 — What is a garbage collector and why do we use them?

public class GarbageCollectorExample {

    public static void main(String[] args) {
        // Creating two new objects of the MyClass class
        MyClass obj1 = new MyClass();
        MyClass obj2 = new MyClass();

        // Setting obj2 to reference to nothing, so as to show how gc works - it will collect that object
        obj2 = null;

        // Requesting garbage collection explicitly
        System.gc();
    }

    static class MyClass {
        // Class implementation
    }

    @Override
    protected void finalize() throws Throwable {
        // Clean-up code executed before gc. => This is the code that you can write to perform any necessary clean-up or resource deallocation before an object is garbage collected.
        // This method is called before reclaiming memory, which you can also perform resource deallocation or cleanup operationsin this method.
        // Also, while people say that It's generally recommended to avoid relying on finalize() for critical operations, you can always use it if you wish to do so.

        // Call the super class finalize() method to execute it.
        super.finalize();
    }
}

public class GarbageCollectorExample {

    public static void main(String[] args) {
        // Creating two new objects of the MyClass class
        MyClass obj1 = new MyClass();
        MyClass obj2 = new MyClass();

        // Setting obj2 to reference to nothing, so as to show how gc works - it will collect that object
        obj2 = null;

        // Requesting garbage collection explicitly
        System.gc();
    }

    static class MyClass {
        // Class implementation
    }

    @Override
    protected void finalize() throws Throwable {
        // Clean-up code executed before gc. => This is the code that you can write to perform any necessary clean-up or resource deallocation before an object is garbage collected.
        // This method is called before reclaiming memory, which you can also perform resource deallocation or cleanup operationsin this method.
        // Also, while people say that It's generally recommended to avoid relying on finalize() for critical operations, you can always use it if you wish to do so.

        // Call the super class finalize() method to execute it.
        super.finalize();
    }
}

String s = "abc"; // String instance, one reference: variable s
s = s + "def"; // Original string instance "abc" is lost, new string instance "abcdef" is stored. Original "abc" is now floating in memory without references
System.gc(); // tells the system to run the garbage collector prematurely; "abc" instance is removed from memory

String s = "abc"; // String instance, one reference: variable s
s = s + "def"; // Original string instance "abc" is lost, new string instance "abcdef" is stored. Original "abc" is now floating in memory without references
System.gc(); // tells the system to run the garbage collector prematurely; "abc" instance is removed from memory

YOUR_DATA_TYPE* someMemory = (YOUR_DATA*) malloc(sizeof(YOUR_DATA_TYPE));//allocate memory
//use the memory somehow
//...
free(someMemory);//give back the memory to the operating system

YOUR_DATA_TYPE* someMemory = (YOUR_DATA*) malloc(sizeof(YOUR_DATA_TYPE));//allocate memory
//use the memory somehow
//...
free(someMemory);//give back the memory to the operating system

Object o = new Object();//create some object stored on the heap
//use the object somehow
//...
//no need to free it - the GC does this for you

Object o = new Object();//create some object stored on the heap
//use the object somehow
//...
//no need to free it - the GC does this for you