Java Oops Ch3 This Finalize Gc

01 Sep 2022

this Keyword

• If the local variables in the class and the parameters for the formal parameters for the method are same then local variables hides the instance variables.
• this can be used inside any method to refer to the current object.

  Example without this Keyword:

class Rectangle
{
   double width;
   double height;
  Rectangle(double width, double height)
  {
    width=width;
    height=width;
  }
  double perimeter()
  {
    double p= 2*(width+height);
    return p;
  }
 }
 class Main
 {
 public static void main(String args[])
 {
   Rectangle rec1=new Rectangle(10,20);
   
   double vol;
   
    vol=rec1.width * rec1.height; 
   System.out.println("Rectangle 1 area:  "+vol);
   System.out.println("Rectangle 1 perimeter method:  "+rec1.perimeter());
  
  
      }
 }

Result:

Rectangle 1 area: 0.0
Rectangle 1 perimeter method: 0.0

Example with this keyword

class Rectangle
{
   double width;
   double height;
  Rectangle(double width, double height)
  {
    this.width=width;
    this.height=width;
  }
  double perimeter()
  {
    double p= 2*(width+height);
    return p;
  }
 }
 class Main
 {
 public static void main(String args[])
 {
   Rectangle rec1=new Rectangle(10,20);
   
   double vol;
   
    vol=rec1.width * rec1.height; 
   System.out.println("Rectangle 1 area:  "+vol);
   System.out.println("Rectangle 1 perimeter method:  "+rec1.perimeter());
  
  
      }
 }

Result:

Rectangle 1 area: 100.0
Rectangle 1 perimeter method: 40.0

Garbage Collection

• When we create an object with new then the dynamic allocation of memory occurs.
• In C++ you have to use keyword delete to manually deallocate the memory.
• But in Java; it deallocated automatically. The technique is called Garbage Collection.
• When no references to an object exist, that object is assumed to be no longer needed, and the memory occupied by the object can be reclaimed.

  Finalize() method

• Sometimes an object will need to perform some action when it is destroyed. For example, if an object is holding some non-Java resource such as a file handle or character font, then you might want to make sure these resources are freed before an object is destroyed. To handle such situations, Java provides a mechanism called finalization.
• finalize( ) is only called just prior to garbage collection.

  Syntax:

protected void finalize( )
{
// finalization code here
}