java基础之反射一 基础API

　　 最近在开发过程中，用到好多反射的知识点，本篇文章复习下反射的内容。

一、创建反射的对象Student

import com.anno.CustomAnno;

public class Student {
    
    @CustomAnno(required = true, length = 30)
    private String name;
    
    @CustomAnno(required = true, length = 3)
    private Integer age;
    
    @CustomAnno(required = false, length = 30)
    private String sex;
    
    @CustomAnno(required = false, length = 20)
    public double weight;
    
    @CustomAnno(required = false, length = 20)
    protected double height;

    public Student() {
        super();
    }
    
    private Student(String name, Integer age) {
        super();
        this.name = name;
        this.age = age;
    }

    public Student(String name, Integer age, String sex) {
        super();
        this.name = name;
        this.age = age;
        this.sex = sex;
    }
    
    public Student(String name, Integer age, String sex, double weight, double height) {
        super();
        this.name = name;
        this.age = age;
        this.sex = sex;
        this.weight = weight;
        this.height = height;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }
    
    public double getWeight() {
        return weight;
    }

    public void setWeight(double weight) {
        this.weight = weight;
    }
    
    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + ", sex=" + sex + "]";
    }
    
    public void show() {
        System.out.println("show()  void");
    }
    
    private String result() {
        return "result  String";
    }
    
    private String result(String result) {
        return result;
    }
}

二、反射有关的基本Api

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class StudentReflect {
    public static void main(String[] args) throws Exception {
        try {
            Class<?> clazz = Class.forName("com.reflect.Student");
            //获取构造器
            System.out.println("----------------获取默认无参构造器：getDeclaredConstructor()---------------");
            Constructor<?> defaultConstructor = clazz.getDeclaredConstructor();
            // 根据构造器创建实例对象
            Student consInstance = (Student) defaultConstructor.newInstance();
            consInstance.setName("李四");
            System.out.println("默认构造器初始化实例对象：" + consInstance);
            
            System.out.println("----------------获取public修饰的有参构造器：getDeclaredConstructor(Class<?>...)----------");
            // 注意参数类型的顺序与构造器中的顺序保持一致
            Constructor<?> constructor = clazz.getDeclaredConstructor(String.class, Integer.class, String.class);
            Object instanceByConstructor = constructor.newInstance("王五", 12, "男");
            System.out.println("有参构造器初始化实例对象：" + instanceByConstructor);
            
            System.out.println("----------------获取private修饰的有参构造器：getDeclaredConstructor(Class<?>...)----------");
            Constructor<?> privateConstruct = clazz.getDeclaredConstructor(String.class, Integer.class);
            privateConstruct.setAccessible(true);
            Object instanceByPrivateConstruct = privateConstruct.newInstance("麻六", 15);
            System.out.println("私有有参构造函数初始化实例对象：" + instanceByPrivateConstruct);
            
            
            // 获取指定的属性名称
            System.out.println("----------------获取指定的属性：getDeclaredField(var)---------------");
            Field nameField = clazz.getDeclaredField("name");
            System.out.println("获取指定属性name的类型：" + nameField.getType());
            // 获取对象实例
            System.out.println("-------------------------实例对象属性赋值----------------------------");
            Object instance = clazz.newInstance();
            // name为私有属性，设置允许访问
            nameField.setAccessible(true);
            // 给实例对象的name属性赋值
            nameField.set(instance, "张三");
            System.out.println("instance实例被赋值后：" + instance);
            System.out.println("--------------------获取public修饰的属性：getFields()--------------------");
            // getFields() 仅能获取public修饰的属性
            Field[] publicFields = clazz.getFields();
            for (Field field : publicFields) {
                System.out.println("获取public修饰的属性名称：" + field.getName());
            }
            System.out.println("-----------------获取所有的属性：getDeclaredFields()---------------------");
            Field[] fields = clazz.getDeclaredFields();
            System.out.print("获取所有的属性名称：");
            for (Field field : fields) {
                field.setAccessible(true);
                System.out.print(field.getName() + "   ");
            }
            System.out.println();
            
            // 获取指定方法
            System.out.println("----------------获取指定的无参方法及调用：getDeclaredMethod(var)---------------");
            Method methodShow = clazz.getDeclaredMethod("show");    
            // 无参方法的调用
            methodShow.invoke(instance);
            
            System.out.println("----------获取指定的有参方法及调用：getDeclaredMethod(var, type)---------");
            Method methodResult = clazz.getDeclaredMethod("result", String.class);
            // 私有方法，需设置允许访问
            methodResult.setAccessible(true);
            String result = (String) methodResult.invoke(instance, "有参方法的反射调用");
            System.out.println(result);
            
            System.out.println("----------------获取所有public修饰的方法(包含父类Object的方法)：getMethods()---------------");
            Method[] publicMethods = clazz.getMethods();
            for (Method method2 : publicMethods) {
                System.out.print(method2.getName() + "   ");
            }
            System.out.println();
            
            System.out.println("----------------获取(Class对象)所有方法：getMethods()---------------");
            Method[] allMethods = clazz.getDeclaredMethods();
            for (Method method2 : allMethods) {
                System.out.print(method2.getName() + "   ");
            }
            
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}