LoginStrategy.java

public interface LoginStrategy {
    public void login();
}

public class UsernamePasswordLogin implements LoginStrategy {
   
    private String username;
    private String password;

    
    public UsernamePasswordLogin(String username, String password) {
        this.username = username;
        this.password = password;
    }

   
    @Override
    public void login() {
       
        System.out.println("Logging in with username and password");
    }
}

public class FacebookLogin implements LoginStrategy {
    
    private FacebookAPI facebookAPI;

    public FacebookLogin(FacebookAPI facebookAPI) {
        this.facebookAPI = facebookAPI;
    }

    @Override
    public void login() {
       
        System.out.println("Logging in with Facebook");
    }
}

public class LoginContext {
   
    private LoginStrategy loginStrategy;

   
    public void setLoginStrategy(LoginStrategy loginStrategy) {
        this.loginStrategy = loginStrategy;
    }

    public void login() {
        loginStrategy.login();
    }
}

Main.java

LoginContext loginContext = new LoginContext();

LoginStrategy usernamePasswordLogin = new UsernamePasswordLogin("user", "pass");


loginContext.setLoginStrategy(usernamePasswordLogin);


loginContext.login();

LoginStrategy facebookLogin = new FacebookLogin(new FacebookAPI());

loginContext.setLoginStrategy(facebookLogin);

loginContext.login();