Instance variable is a variable declared within the class for which every object of the class has its own value.
In Java, making a class field public can cause lot of issues in a program. For instance you may have a class called MyCompany. This class contains an array of String companies.
You may have assume that this array will always contain 4 names of companies. But as this array is public, it may be accessed by anyone. Someone by mistake also may change the value and insert a bug!
public class MyCompany {
public String[] companies =
{"Google", "Yahoo", "Microsoft", "Paypal"};
//some code
}
Best approach as many of you already know is to always make the field private and add a getter method to access the elements.
private String[] companies =
{"Google", "Yahoo", "Microsoft", "Paypal"};
public String[] getCompanies() {
return companies; // imperfect code
}
But writing getter method does not exactly solve our problem. The array is still accessible. Best way to make it unmodifiable is to return a clone of array instead of array itself. Thus the getter method will be changed to.
public String[] getCompanies() {
return companies.clone(); // better code
}
Bonus Diagram:
