工厂模式主要解决接口选择的问题，相对比较简单，而且常用。

一、需求举例：

项目中需求开发应用场景：
1.如果初级工程师能够完成，就让初级工程师完成，否则交给中级工程师；
2.如果中级工程师能够完成，就让中级工程师完成，否则交给高级工程师；
3.如果高级工程师能够完成，就让高级工程师完成，否则交给Top工程师拒绝需求；

二、代码实例

父类接口：Engineer.java

package com.lance.factory;

public interface Engineer {

    int EASY = 1;
    int MIDDLE = 2;
    int DIFFICULT = 3;

    default void develop(String program) {
        System.out.println("Engineer default refuse " + program);
    }
}

初级工程师类：JuniorEngineer.java

package com.lance.factory;

public class JuniorEngineer implements Engineer{

    @Override
    public void develop(String program) {
        System.out.println("Junior Engineer finish " + program);

    }

}

中级工程师类: IntermediateEngineer.java

package com.lance.factory;

public class IntermediateEngineer implements Engineer {

    @Override
    public void develop(String program) {
        System.out.println("Intermediate Engineer finish " + program);
    }
}

高级工程师类:SeniorEngineer.java

package com.lance.factory;

public class SeniorEngineer implements Engineer{

    @Override
    public void develop(String program) {
        System.out.println("Senior Engineer finish " + program);

    }
}

工程师工厂类：EngineerFactory.java

package com.lance.factory;

public class EngineerFactory {

     static Engineer getEngineer(int difficulty) {
        Engineer engineer = null;

        switch (difficulty) {
            case Engineer.EASY:
                engineer = new JuniorEngineer();
                break;
            case Engineer.MIDDLE:
                engineer = new IntermediateEngineer();
                break;
            case Engineer.DIFFICULT:
                engineer = new SeniorEngineer();
                break;
            default:
                engineer = new Engineer() {
                };
                break;


        }



        return engineer;
    }
}

工厂模式主类: FactoryPattern.java

package com.lance.factory;

public class FactoryPattern {
    public static void main(String[] args) {


        System.out.println("==========start==========");
        Engineer engineer = EngineerFactory.getEngineer(Engineer.EASY);
        engineer.develop("easy program");

        System.out.println("=======================");

        engineer = EngineerFactory.getEngineer(Engineer.MIDDLE);
        engineer.develop("middle program");

        System.out.println("=======================");

        engineer = EngineerFactory.getEngineer(Engineer.DIFFICULT);
        engineer.develop("difficult program");

        System.out.println("=======================");

        engineer = EngineerFactory.getEngineer(100);
        engineer.develop("too difficult program");

        System.out.println("==========end==========");

    }
}

输出结果：

==========start==========
Junior Engineer finish easy program
=======================
Intermediate Engineer finish middle program
=======================
Senior Engineer finish difficult program
=======================
Engineer default refuse too difficult program
==========end==========