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Java Observable setChanged() Method with Example

Observable Class setChanged() method: Here, we are going to learn about the setChanged() method of Observable Class with its syntax and example.
Submitted by Preeti Jain, on March 04, 2020

Observable Class setChanged() method

• setChanged() method is available in java.util package.
• setChanged() method is used to set this Observable object status as changed.
• setChanged() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
• setChanged() method does not throw an exception at the time of set changing status.

Syntax:

    protected void setChanged();

Parameter(s):

• It does not accept any parameter.

Return value:

The return type of the method is void, it returns nothing.

Example:

// Java program to demonstrate the example 
// of void setChanged() method of Observable

import java.util.*;

// Implement Observers class 
class Observers implements Observer {
    public void update(Observable obj, Object ob) {
        System.out.println("Obs is added");
    }
}

// Implement Observed Class
class Observed extends Observable {
    // Function call with setChanged()
    void setChange() {
        setChanged();
        System.out.println("setChanged(): " + hasChanged());
        notifyObservers();
    }

    // Function call without setChanged()
    void unsetChange() {
        System.out.println("unsetChanged(): " + hasChanged());
        notifyObservers();
    }
}

public class SetChanged {
    // Implement Main Method
    public static void main(String args[]) {
        Observed observed = new Observed();
        Observers obs = new Observers();
        observed.addObserver(obs);
        observed.setChange();
        observed.unsetChange();
    }
}

Output

setChanged(): true
Obs is added
unsetChanged(): false