主要用到概念：接口，抽象方法，覆写，static定义变量，主方法中的匿名对象使用。

代码如下：

package factory;

interface fruit {
    public abstract void eat();
}

class Apple implements fruit {
    public void eat() {
        System.out.println("eat apple");
    }
}

class Orange implements fruit {
    public void eat() {
        System.out.println("eat orange");
    }
}

class Banana implements fruit {
    public void eat() {
        System.out.println("eat banana");
    }
}

class factory {
    public static String APPLE = "apple";
    public static String ORANGE = "orange";
    public static String BANANA = "banana";

    public static fruit getInstance(String className) {
        if (APPLE.equals(className)) {
            return new Apple();
        } else if (ORANGE.equals(className)) {
            return new Orange();
        } else if (BANANA.equals(className)) {
            return new Banana();
        }
        return null;
    }
}

public class demo {
    public static void main(String[] args) {
        fruit f = factory.getInstance("apple");
        f.eat();
    }
}