new and this keywords

"new " and "this" keywords

The "new" keyword

The new keyword does the following tasks for us,


• Dynamically allocates memory for the object on heap space.
• Creates object reference on the heap stack.
• Returns a reference to this object.
• Reference is stored in a variable.

The objects can be declared using object reference, such as

 Employee employee;
 Student student;

An object is created by using the new keyword and class constructor.

Employee employee=new Employee();
Student student=new Student();

The "this" keyword

• Each class member function has an implicit reference to its own class object, named “this”.
• this implicit reference is created automatically by the compiler itself.
• It returns the reference of the object from which it is invoked.
• "this" keyword enables us to resolve the name collision between member variable and method arguments.
• this can also be used to refer to overloaded(see Polymorphism in Java) class constructors.
• It can’t be used with static methods.

For example

public class Circle {

float radius;
static float pi=3.14f;
public Circle() { 

}

public Circle(float radius)
{
 this(); //referring constructor 
 this.radius=radius*(pi);
}
}

Using new and this together

class Box{

 int h,w,l;
 public Box(int h, int w, int l) {
  super();
  this.h = h;
  this.w = w;
  this.l = l;
 }

 public void displayVolume()
 {
  System.out.println("Volume "+ h*w*l);
 }

}

public class ArrayTest {

 public static void main(String[] args) {
 Box box[]=new Box[5];// create an Array of Boxes
 box[0]=new Box(10,21,13);//create five Boxes
 box[1]=new Box(11,19,44);//Add to Array box[]
 box[2]=new Box(21,17,26);
 box[3]=new Box(14,11,28);
 box[4]=new Box(17,22,19);

 for(Box b:box)
 {
  b.displayVolume();
 }

}
}

Video Tutorial