So, the constructor is usually passed parameters, and it sets the values of the attributes according to these parameters. 

For example, a class that models a book:
class Book {
    String name;
    String writer;
    int pages;
    int releaseYear;

    
    public Book(String n, String w, int p, int ry) {
        name = n;
        writer = w;
        pages = p;
        releaseYear = ry;
    }
}
 

In the example, you will notice that the PARAMETER NAMES are somewhat clumsy ABBREVIATIONS of the attribute names.
Now, when calling the constructor, it is not at all clear what the parameters actually mean.


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A better way is to USE the SAME IDENTIFIERS for parameters and attributes. 
This can be done by using the keyword 'this':

class Book {
    String name;
    String writer;
    int pages;
    int releaseYear;
	
    public Book(String name, String writer, int pages, int releaseYear) {
        this.name = name;
        this.writer = writer;
        this.pages = pages;
        this.releaseYear = releaseYear;
    }
}
 

The keyword 'this' refers to the CURRENT OBJECT.

Thus the entry
'this.name'
always refers to the attribute name of the object.


In the constructor above, the statement
this.name = name;
sets the attribute value to the name received as a parameter. 
In effect, the name given by the client is set as the value of the name field of the new object to be created.