反射的案例

太过爱你忘了你带给我的痛 2024-04-08 13:21 9阅读 0赞

#### 1.反射获取构造方法并使用练习1【应用】 ####

*  案例需求
    
     *  通过反射获取公共的构造方法并创建对象
 *  代码实现
    
     *  学生类

public class Student {
        //成员变量：一个私有，一个默认，一个公共
        private String name;
        int age;
        public String address;
    
        //构造方法：一个私有，一个默认，两个公共
        public Student() {
        }
    
        private Student(String name) {
            this.name = name;
        }
    
        Student(String name, int age) {
            this.name = name;
            this.age = age;
        }
    
        public Student(String name, int age, String address) {
            this.name = name;
            this.age = age;
            this.address = address;
        }
    
        //成员方法：一个私有，四个公共
        private void function() {
            System.out.println("function");
        }
    
        public void method1() {
            System.out.println("method");
        }
    
        public void method2(String s) {
            System.out.println("method:" + s);
        }
    
        public String method3(String s, int i) {
            return s + "," + i;
        }
    
        @Override
        public String toString() {
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", address='" + address + '\'' +
                    '}';
        }
    }

测试类

public class ReflectDemo02 {
        public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
            //获取Class对象
            Class<?> c = Class.forName("com.itheima_02.Student");
    
            //public Student(String name, int age, String address)
            //Constructor<T> getConstructor(Class<?>... parameterTypes)
            Constructor<?> con = c.getConstructor(String.class, int.class, String.class);
            //基本数据类型也可以通过.class得到对应的Class类型
    
            //T newInstance(Object... initargs)
            Object obj = con.newInstance("林青霞", 30, "西安");
            System.out.println(obj);
        }
    }

#### 2.反射获取构造方法并使用练习2【应用】 ####

*  案例需求
    
     *  通过反射获取私有构造方法并创建对象
 *  代码实现
    
     *  学生类：参见上方学生类
     *  测试类

public class ReflectDemo03 {
        public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
            //获取Class对象
            Class<?> c = Class.forName("com.itheima_02.Student");
    
            //private Student(String name)
            //Constructor<T> getDeclaredConstructor(Class<?>... parameterTypes)
            Constructor<?> con = c.getDeclaredConstructor(String.class);
    
            //暴力反射
            //public void setAccessible(boolean flag):值为true，取消访问检查
            con.setAccessible(true);
    
            Object obj = con.newInstance("林青霞");
            System.out.println(obj);
        }
    }

#### 3.反射获取成员变量并使用练习【应用】 ####

*  案例需求
    
     *  通过反射获取成员变量并赋值
 *  代码实现
    
     *  学生类：参见上方学生类
     *  测试类

public class ReflectDemo02 {
        public static void main(String[] args) throws Exception {
            //获取Class对象
            Class<?> c = Class.forName("com.itheima_02.Student");
    
            //Student s = new Student();
            Constructor<?> con = c.getConstructor();
            Object obj = con.newInstance();
            System.out.println(obj);
    
            //s.name = "林青霞";
    //        Field nameField = c.getField("name"); //NoSuchFieldException: name
            Field nameField = c.getDeclaredField("name");
            nameField.setAccessible(true);
            nameField.set(obj, "林青霞");
            System.out.println(obj);
    
            //s.age = 30;
            Field ageField = c.getDeclaredField("age");
            ageField.setAccessible(true);
            ageField.set(obj,30);
            System.out.println(obj);
    
            //s.address = "西安";
            Field addressField = c.getDeclaredField("address");
            addressField.setAccessible(true);
            addressField.set(obj,"西安");
            System.out.println(obj);
        }
    }

#### 4.反射获取成员方法并使用练习【应用】 ####

*  案例需求
    
     *  通过反射获取成员方法并调用
 *  代码实现
    
     *  学生类：参见上方学生类
     *  测试类

public class ReflectDemo02 {
        public static void main(String[] args) throws Exception {
            //获取Class对象
            Class<?> c = Class.forName("com.itheima_02.Student");
    
            //Student s = new Student();
            Constructor<?> con = c.getConstructor();
            Object obj = con.newInstance();
    
            //s.method1();
            Method m1 = c.getMethod("method1");
            m1.invoke(obj);
    
            //s.method2("林青霞");
            Method m2 = c.getMethod("method2", String.class);
            m2.invoke(obj,"林青霞");
    
    //        String ss = s.method3("林青霞",30);
    //        System.out.println(ss);
            Method m3 = c.getMethod("method3", String.class, int.class);
            Object o = m3.invoke(obj, "林青霞", 30);
            System.out.println(o);
    
            //s.function();
    //        Method m4 = c.getMethod("function"); //NoSuchMethodException: com.itheima_02.Student.function()
            Method m4 = c.getDeclaredMethod("function");
            m4.setAccessible(true);
            m4.invoke(obj);
        }
    }

#### 5.反射练习之越过泛型检查 ####

*  案例需求
    
     *  通过反射技术，向一个泛型为Integer的集合中添加一些字符串数据
 *  代码实现
 *      public class ReflectTest01 {
            public static void main(String[] args) throws Exception {
                //创建集合
                ArrayList<Integer> array = new ArrayList<Integer>();
        
        //        array.add(10);
        //        array.add(20);
        //        array.add("hello");
        
                Class<? extends ArrayList> c = array.getClass();
                Method m = c.getMethod("add", Object.class);
        
                m.invoke(array,"hello");
                m.invoke(array,"world");
                m.invoke(array,"java");
        
                System.out.println(array);
            }
        }

#### 6.运行配置文件中指定类的指定方法 ####

*  案例需求
    
     *  通过反射运行配置文件中指定类的指定方法
 *  代码实现

public class ReflectTest02 {
        public static void main(String[] args) throws Exception {
            //加载数据
            Properties prop = new Properties();
            FileReader fr = new FileReader("myReflect\\class.txt");
            prop.load(fr);
            fr.close();
    
            /*
                className=com.itheima_06.Student
                methodName=study
             */
            String className = prop.getProperty("className");
            String methodName = prop.getProperty("methodName");
    
            //通过反射来使用
            Class<?> c = Class.forName(className);//com.itheima_06.Student
    
            Constructor<?> con = c.getConstructor();
            Object obj = con.newInstance();
    
            Method m = c.getMethod(methodName);//study
            m.invoke(obj);
        }
    }