Advantage of set and get methods vs public variable [duplicate]

What I have seen someday on SO, as answer (written by @ChssPly76) why to use getters and setters

Because 2 weeks (months, years) from now when you realize that your setter needs to do more than just set the value, you'll also realize that the property has been used directly in 238 other classes :-)

there are much more advantages:

1. getters and setter can have validation in them, fields can't
2. using getter you can get subclass of wanted class.
3. getters and setters are polymorphic, fields aren't
4. debugging can be much simpler, because breakpoint can be placed inside one method not near many references of that given field.
5. they can hide implementation changes:

before:

private boolean alive = true;public boolean isAlive() { return alive; }public void setAlive(boolean alive) { this.alive = alive; }

after:

private int hp; // change!public boolean isAlive() { return hp > 0; } // old signature  //method looks the same, no change in client codepublic void setAlive(boolean alive) { this.hp = alive ? 100 : 0; }

EDIT: one additional new advange when you are using Eclipse - you can create watchpoint on field, but if you have setter you need just a breakpoint, and... breakpoints (e.g. in setter method) can be conditional, watchpoints (on field) cannot. So if you want to stop your debugger only if x=10 you can do it only with breakpoint inside setter.

Using public variable can cause setting wrong values to the variable as the input value cannot be checked.

eg:

 public class A{    public int x;   // Value can be directly assigned to x without checking.   }

Using setter can be used to set the variable with checking the input. Keeping the instance varibale private, and getter and setter public is a form of Encapsulationgetter and setter is also compatible with Java Beans standard,

getter and setter alsohelps in implementing polymorphism concept

eg:

public class A{     private int x;      //      public void setX(int x){       if (x>0){                     // Checking of Value        this.x = x;       }       else{           System.out.println("Input invalid");         }     }      public int getX(){          return this.x;       }

Polymorphic example: We can assign Object Refernce Variable of the Sub type as Argument from Calling method to the Object Refernce Variable of Super Class Parameter of the Called method.

public class Animal{       public void setSound(Animal a) {          if (a instanceof Dog) {         // Checking animal type                System.out.println("Bark");             }         else if (a instanceof Cat) {     // Checking animal type                 System.out.println("Meowww");             }         }      }

1. Some libraries require this to fulfill the "Java Bean standard".
2. A setter/getter can be in an interface, a property cannot be in an interface
3. Setters/getters can easily be overridden in descended classes.
4. setters/getters abstract away the information whether a value is calculated on demand or just an accessor to a property