OBJECTS AND CLASSES - Introduction to Java Programming: Comprehensive Version - page 356

Tip
To avoid confusion and mistakes, do not use the names of instance or static variables as
local variable names, except for method parameters.

9.31

✓ ✓

What is the output of the following program?

Check

Point

public class Test {
private static int i = 0 ;
private static int j = 0 ;

public static void main(String[] args) {
int i = 2 ;
int k = 3 ;

{

int j = 3 ;
System.out.println( "i + j is " + i + j);
}

k = i + j;
System.out.println( "k is " + k);
System.out.println( "j is " + j);
}
}

9.14 The this Reference
The keyword this refers to the object itself. It can also be used inside a constructor to
invoke another constructor of the same class.

Key
Point

The this keyword is the name of a reference that an object can use to refer to itself. You can
use the this keyword to reference the object's instance members. For example, the following
code in (a) uses this to reference the object's radius and invokes its getArea() method
explicitly. The this reference is normally omitted, as shown in (b). However, the this
reference is needed to reference hidden data fields or invoke an overloaded constructor.

this keyword

public class Circle {
private double radius;

public class Circle {
private double radius;

... ...

public double getArea() {
return this . radius * this . radius * Math.PI;
}

public double getArea() {
return radius * radius * Math.PI;

Equivalent

}

public String toString() {
return "radius: " + this . radius
+ "area: " + this .getArea() ;

public String toString() {
return "radius: " + radius
+ "area: " + getArea() ;

}
}

}
}

(a) (b)

9.14.1 Using this to Reference Hidden Data Fields
The this keyword can be used to reference a class's hidden data fields . For example, a data-
field name is often used as the parameter name in a setter method for the data field. In this
case, the data field is hidden in the setter method. You need to reference the hidden data-field
name in the method in order to set a new value to it. A hidden static variable can be accessed

hidden data fields