Classes and Objects - Beginning Java 8 Fundamentals - page 203

Listing 6-13. Using the this Keyword to Refer to an Instance Variable Whose Name Is Hidden by a Local Variable
// ThisTest6.java
package com.jdojo.cls;
public class ThisTest6 {
int num = 1982; // An instance variable
void printNum(int num) {
System.out.println("Parameter num: " + num);
System.out.println("Instance variable num: " + this.num);
}
public static void main(String[] args) {
ThisTest6 tt6 = new ThisTest6();
tt6.printNum(1969);
}
}
Parameter num: 1969
Instance variable num: 1982
The output of ThisTest6 shows the expected result. If you do not want to use the keyword this , you can rename
the parameter of the printNum() method, like so:
void printNum(int numParam) {
System.out.println("Parameter num: " + numParam);
System.out.println("Instance variable num: " + num);
}
Once you rename the parameter to something other than num , the num instance variable is no longer hidden
inside the body of the printNum() method, and therefore you can refer to it using its simple name.
You can use the keyword this to refer to the instance variable num inside the printNum() method even if it
is not hidden as shown below. However, using the keyword this in the following case is a matter of choice, not a
requirement.
void printNum(int numParam) {
System.out.println("Parameter num: " + numParam);
System.out.println("Instance variable num: " + this.num);
}
In the previous example, you saw that use of the keyword this is necessary to access instance variables when
the instance variable name is hidden. You can avoid using the keyword this in such circumstances by renaming the
variable that hides the instance variable name, or renaming the instance variable itself. Sometimes it is easier to keep
the variable names the same, as they represent the same thing. This topic uses the convention of using the same name
for instance variables and local variables if they represent the same thing in the class. For example, the following code
is very common:
public class Student {
private int id; // An instance variable