017 Java反射机制，一个实例讲述java反射的方法

Bertha 。 2023-01-17 07:54 139阅读 0赞

太多的框架使用到Java的反射，彰显的Java反射异常重要。  
反射是Java一个非常重要的高级特性。本章介绍一下Java反射。

**Java反射机制**是在程序运行过程中，对任何一个类，都能够知道它的所有属性和方法；并对这些属性和方法进行调用，称为动态调用，这种动态获取信息和动态调用对象方法的功能称为Java的反射机制。

Java反射机制主要功能：

*  在运行时判断任意一个对象所属的类。
 *  在运行时构造任意一个类的对象。
 *  在运行时判断任意一个类的所有成员变量和方法。
 *  在运行时调用任意一个对象的方法。

一个示例讲述Java反射：

package com.lingyiwin.test;
    
    import java.lang.reflect.Constructor;
    import java.lang.reflect.Field;
    import java.lang.reflect.Method;
    
    public class TestReflect { 
        public static void main(String[] args) throws Exception { 
            Class student = null;
    
            try { 
                student = Class.forName("com.lingyiwin.test.Student");
            } catch (ClassNotFoundException e) { 
                e.printStackTrace();
            }
    
            System.out.println("获取student的所有共有属性");
            Field[] fields = student.getFields();
            for (Field field : fields) { 
                System.out.println(field);
            }
    
            System.out.println("\n获取student的所有属性,不包含继承的属性");
            Field[] declaredFields = student.getDeclaredFields();
            for (Field declaredField : declaredFields) { 
                System.out.println(declaredField);
            }
    
            System.out.println("\n获取student的所有公共方法");
            Method[] methods = student.getMethods();
            for (Method method : methods) { 
                System.out.println(method);
            }
    
            System.out.println("\n获取student的所有公共方法,不包含继承的属性");
            Method[] declaredMethods = student.getDeclaredMethods();
            for (Method declaredMethod : declaredMethods) { 
                System.out.println(declaredMethod);
            }
    
            System.out.println("\n获取student的所有公共构造方法");
            Constructor[] declaredConstructors = student.getDeclaredConstructors();
            for (Constructor declaredConstructor : declaredConstructors) { 
                System.out.println(declaredConstructor);
            }
    
            System.out.println("\n使用默认构造函数实例化student.newInstance() 一定要有默认无参的构造函数。否则会报错");
            Student instance = (Student) student.newInstance();
            instance.setAddress("上海");
            System.out.println(instance.toString());
    
            System.out.println("\n使用构造函数 Student(String className) 实例化");
            Constructor constructor = student.getConstructor(String.class);
            Student st = (Student) constructor.newInstance("班级名称");
            System.out.println(st.toString());
    
            System.out.println("\n使用构造函数 Student(String name, int age, String className, String address) 实例化");
            Constructor ct = student.getConstructor(String.class, int.class, String.class, String.class);
            Student st1 = (Student) ct.newInstance("小明", 18, "班级名称", "上海");
            System.out.println(st1.toString());
    
            System.out.println("\n获取无参的方法并执行:");
            Method learn = student.getMethod("learn");
            learn.invoke(st1);
    
            System.out.println("\n获取有参的方法并执行:");
            Method readBook = student.getMethod("readBook",String.class);
            String str = (String) readBook.invoke(st1,"语文");
            System.out.println("方法返回值：" + str);
        }
    }

package com.lingyiwin.test;
    
    public class Student extends Person implements Study { 
        public String className;
        private String address;
    
        public String getClassName() { 
            return className;
        }
    
        public void setClassName(String className) { 
            this.className = className;
        }
    
        public String getAddress() { 
            return address;
        }
    
        public void setAddress(String address) { 
            this.address = address;
        }
    
        public Student(String name, int age, String className, String address) { 
            super(name, age);
            this.className = className;
            this.address = address;
        }
    
        public Student() { 
        }
    
        public Student(String className) { 
            this.className = className;
        }
    
        @Override
        public String toString() { 
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", className='" + className + '\'' +
                    ", address='" + address + '\'' +
                    '}';
        }
    
        @Override
        public void learn() { 
            System.out.println("实现study接口");
        }
    
        public String readBook(String book) { 
            System.out.println("学生读书");
            return this.name + "读" + book;
        }
    }

package com.lingyiwin.test;
    
    public class Person { 
        public String name;
        public int age;
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public int getAge() { 
            return age;
        }
    
        public void setAge(int age) { 
            this.age = age;
        }
    
        public Person() { 
            super();
        }
    
        public Person(String name, int age) { 
            super();
            this.name = name;
            this.age = age;
        }
    
        public String showInfo() { 
            return "name:" + name + ",age:" + age;
        }
    }

package com.lingyiwin.test;
    
    public interface Study { 
        public void learn();
    }

众多方法，还请参考API，上面仅仅只有部分常用的。