Question

我正在运行此代码，但是却收到此错误消息，无法解决。在反射的帮助下，要求使用工厂模式设计任何Java代码。在下面，我添加了我运行代码并再次输入文件名和类名TestReflectionFactoryDesign时出现的错误消息。

错误消息：

Exception in thread "main" java.lang.ClassNotFoundException: com.test.TestReflectionFactoryDesign.Student
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:264)
    at PersonFactory.getPersonWithFullQualifiedClassName(TestReflectionFactoryDesign.java:58)
    at TestReflectionFactoryDesign.main(TestReflectionFactoryDesign.java:6)

代码：

public class TestReflectionFactoryDesign {
    public static void main(String[] args) throws Exception {
        Person student = PersonFactory.getPersonWithFullQualifiedClassName("com.test.TestReflectionFactoryDesign.Student");    
        student.say();    
        Person teacher = PersonFactory.getPersonWithClass(Teacher.class);    
        teacher.say();   
        Person student2 = PersonFactory.getPersonWithName("student");    
        student2.say();   
    }    
}

class Student implements Person {    
    @Override    
    public void say() {    
        System.out.println("I am a student");    
    }    
}

class Teacher implements Person {    
    @Override    
    public void say() {   
        System.out.println("I am a teacher");    
    }    
}

interface Person {    
    void say();    
}

class PersonFactory {    
    // reflection, by full qualified class name    
    public static Person getPersonWithFullQualifiedClassName(String personType) throws Exception {    
        Class<?> personClass = Class.forName(personType);   
        return getPersonWithClass(personClass);    
    }

    // reflection, by passing class object   
    public static Person getPersonWithClass(Class personClass) throws Exception {  
        return (Person) personClass.newInstance();    
    }

    // no reflection, the ordinary way    
    public static Person getPersonWithName(String personType) {    
        if (personType.equalsIgnoreCase("STUDENT")) {    
            return new Student();    
        } else if (personType.equalsIgnoreCase("TEACHER")) {    
            return new Teacher();   
        }   
        return null;    
    }    
}

Answer 1

由于您（很可能）没有在包的下面声明您的类，因此在类的第一行中使用了package xxx.yyy.zzz，因此Java认为它是未命名（默认）包的一部分。已经说明了here

您可以通过将包设置为班级文件（最推荐）或更改完全合格的班级名称以删除无效的包（只需保留Student）来解决此问题。

Answer 2

如果仅是通过反射来学习工厂模式，那么一个简单的解决方案是，使用您喜欢的文本编辑器将下面的代码复制到TestReflectionFactoryDesign.java文件中，然后转到保存它的路径并运行javac TestReflectionFactoryDesign.java，然后java TestReflectionFactoryDesign查看结果。

public class TestReflectionFactoryDesign {
    public static void main(String[] args) throws Exception {
        Person student = PersonFactory.getPersonWithFullQualifiedClassName("Student");    
        student.say();    
        Person teacher = PersonFactory.getPersonWithClass(Teacher.class);    
        teacher.say();   
        Person student2 = PersonFactory.getPersonWithName("student");    
        student2.say();   
    }    
}

class Student implements Person {    
    @Override    
    public void say() {    
        System.out.println("I am a student");    
    }    
}

class Teacher implements Person {    
    @Override    
    public void say() {   
        System.out.println("I am a teacher");    
    }    
}

interface Person {    
    void say();    
}

class PersonFactory {    
    // reflection, by full qualified class name    
    public static Person getPersonWithFullQualifiedClassName(String personType) throws Exception {    
        Class<?> personClass = Class.forName(personType);   
        return getPersonWithClass(personClass);    
    }

    // reflection, by passing class object   
    public static Person getPersonWithClass(Class personClass) throws Exception {  
        return (Person) personClass.newInstance();    
    }

    // no reflection, the ordinary way    
    public static Person getPersonWithName(String personType) {    
        if (personType.equalsIgnoreCase("STUDENT")) {    
            return new Student();    
        } else if (personType.equalsIgnoreCase("TEACHER")) {    
            return new Teacher();   
        }   
        return null;    
    }    
}

如果您在IDE中，并且不想更改代码，则应在代码的开始处放置package com.test.TestReflectionFactoryDesign，这应该是创建Java文件的路径。

用工厂模式实现反射

2 个答案: