factory

 Factory Method：定义一个用于创建对象的接口，让子类决定将哪一个类实例化。Factory Method使一个类的实例化延迟到其子类。

step1: define a abstract class , for example Windows;

step2:define subclasses of the abstract class, for example BigWindows, SmallWindows

step3:define a method in the factory class which returns a Window instance

 

code:

 

step1

public abstract class Window {
    public abstract void func();
}

 

step2
public class WindowBig extends Window {
    public void func() {
        System.out.println("This is Big Window !");
    }
}

 

public class WindowSmall extends Window {
    public void func() {
        System.out.println("This is Small Window !");
    }
}

 

step3

public class Factory {
    public Window CreateWindow (String type) {
        if(type.equals("Big")) {
            return new WindowBig();
        } else if(type.equals("Small")) {
            return new WindowSmall();
        } else {
            return new WindowBig();
        }
    }

    // The Main function only for our test
    public static void main(String[] args) {
        Factory myFactory = new Factory();
        Window myBigWindow = myFactory.CreateWindow("Big");
        myBigWindow.func();

        Window mySmallWindow = myFactory.CreateWindow("Small");
        mySmallWindow.func();
    }
}