Difference between Page Object Model and Page Factory

POM:
_____
By username=By.name("userName");


PageFactory:
____________
// Defining Locators
@FindBy(name="userName")
WebElement userName;



POM:
____
Signon(WebDriver driver)
{
this.driver=driver;
}





PageFactory:
_____________

SignonPF(WebDriver driver)
{
this.driver=driver;
PageFactory.initElements(driver, this);
}


POM:
____

public void enterUsername(String name)
{
driver.findElement(username).sendKeys(name);
}


PageFactory:
____________

public void enterUser(String name)
{
userName.sendKeys(name);
}