Instance Variable Hiding

this Keyword

• this is a pointer that points to the current object
• this keyword is used when a method need to refer to the object that invoked it.
• this can be used inside any method to refer to the current object
• Consider the following Example:

//redundant use of this
Box(double w, double h, double d)
{
    this.width=w;
    this.height=h;
    this.depth=d;
}

Instance Variable Hiding

• It is illegal in java to declare two local variables with the same name inside the same or enclosing scopes.
• We have local variables, including formal parameters to methods, which overlap with the names of the class’ instance variables.
• However, when a local variable has the same name as an instance variable, the local variable hides the instance variable.
• This is why width, height and depth were not used as the names of the parameters to the Box() constructor inside the box class.
• If they had been, then width would have referred to the formal parameter, hiding the instance variable width. While it is easier to use different names.
• this can be used to resolve any name space collisions that might occur between instance variables and local variables because it refers to the current object
• For example, here is another version of Box(), which uses width, height, and depth for parameter names and then uses this to access the instance variables by the same name.

// use of this to resolve naming collisions.
Box(double width, double height, double depth)
{
    this.width=width;
    this.height=height;
    this.depth=depth;
}