Observer Pattern

Observer Pattern:Observer Pattern defines a one-to-many dependency between objects so that when on object changes state, all its dependents are notified and updated accordingly.

Example 1 using custom Observable and Observer Interface

Observable.java

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package com.observerpattern.example;   public interface Observable {  public void registerObserver(Observer observer);  public void notifyObsevers(); }

Observer.java

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package com.observerpattern.example;   public interface Observer {  public void update(float salary); }

Account.java

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package com.observerpattern.example;   import java.util.ArrayList; import java.util.List;   public class Account implements Observable {  float salary;  List<observer> listObserver = new ArrayList<>();    public void setSalary(float salary) {   this.salary = salary;   System.out.println("Salary Credited successfully into Account");   salaryCredited();  }    public void salaryCredited() {   notifyObsevers();  }    @Override  public void registerObserver(Observer observer) {   listObserver.add(observer);  }    @Override  public void notifyObsevers() {   for (Observer observer : listObserver) {    observer.update(this.salary);   }    }    public float getSalary() {   return salary;  }   } </observer>

Bank.java

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package com.observerpattern.example;   public class Bank implements Observer {     Observable account;  float salary;    public Bank(Observable account) {   this.account = account;   account.registerObserver(this);  }    @Override  public void update(float salary) {   this.salary = salary;   if(this.salary > 0){    System.out.println("EMI Amount successfully deducted from your Account");   }else{    System.out.println("Account doesn't have sufficient balance for emi deduction");   }  }   }

AccountTestDrive.java

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package com.observerpattern.example;   public class AccountTestDrive {  public static void main(String[] args) {   Account account = new Account();   Bank bank = new Bank(account);   //when salary is credited into Account(Observable),Bank(Observer) will be notified   account.setSalary(100000);  } }

Example 2 using java.util Observable Interface and Observer class

Account.java

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package com.observerpattern.example2;   import java.util.Observable;   public class Account extends Observable {  float salary;    public void setSalary(float salary) {   this.salary = salary;   System.out.println("Salary Credited successfully into Account");   salaryCredited();  }     public void salaryCredited(){   setChanged();   notifyObservers();  }    public float getSalary() {   return salary;  }    }

Bank.java

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package com.observerpattern.example2;   import java.util.Observable; import java.util.Observer;   public class Bank implements Observer {     Observable account;    public Bank(Observable account) {   this.account = account;   account.addObserver(this);  }    @Override  public void update(Observable account, Object object) {   if(account instanceof Observable){    Account salaryAccount = (Account) account;    if(salaryAccount.getSalary() > 0){     System.out.println("EMI Amount successfully deducted from your Account");    }else{     System.out.println("Account doesn't have sufficient balance for emi deduction");    }   }  }   }

AccountTestDrive.java

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package com.observerpattern.example;   public class AccountTestDrive {  public static void main(String[] args) {   Account account = new Account();   Bank bank = new Bank(account);   //when salary is credited into Account(Observable),Bank(Observer) will be notified   account.setSalary(100000);  } }

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