Java反射的基本应用-白红宇

Java反射的基本应用

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发布时间：2019-05-10

本文共 9616 字，大约阅读时间需要 32 分钟。

反射机制,程序在运行时加载新的类,使程序更加灵活

public class HelooReflect {    public static void main(String[] args) {        // 获取类        testClass();    }    private static void testClass() {        // 创建一个学生类的对象        Student student = new Student();        try {            // 开始获取类            Class clazz1 = Student.class;            Class clazz2 = student.getClass();            Class clazz3 = Class.forName("com.bjsxt.java.clc.fanshe.Student");            //判断类对象是否相等            System.out.println(clazz1 == clazz2);            System.out.println(clazz1 == clazz3);            //常见 方法            System.out.println("类的名字" + clazz1.getName());            System.out.println("类的简称" + clazz1.getSimpleName());            System.out.println("包的信息" + clazz1.getPackage().getName());            System.out.println("获取包名" + clazz1.getPackage());            System.out.println("获取修饰符" + clazz1.getModifiers());            System.out.println("获取父类" + clazz1.getSuperclass());            System.out.println("获取父类的超类" + clazz1.getGenericSuperclass());            System.out.println("判断是否为接口" + clazz1.isInterface());            System.out.println("获取类加载器" + clazz1.getClassLoader());                        //基本类型9=(8种基本数据类型的类+1void)            System.out.println(int.class == Integer.class);//不等            //判断是否是基本类型            System.out.println(int.class.isPrimitive());            System.out.println(Integer.class.isPrimitive());            System.out.println("数组是引用类型" + int[].class.isPrimitive());        } catch (ClassNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }}

获取类的名字,方法,属性,构造器

import java.lang.reflect.Constructor;import java.lang.reflect.Field;import java.lang.reflect.Method;public class Test2 {    public static void main(String[] args) {        try {            Class clazz = Class.forName("bean.User");            // 获取类的名字            clazz.getName();            /**             * 获取属性信息             */            // 只能获取public的属性            Field[] fields1 = clazz.getFields();            // 可以获得所有的属性            Field[] fields2 = clazz.getDeclaredFields();            // 输出获取到的属性的个数            System.out.println(fields1.length);            System.out.println(fields2.length);            // 遍历获取到的属性            for (Field field : fields2) {                System.out.println("属性" + field);            }            // 获得属性的权限            Field f = clazz.getDeclaredField("uname");            System.out.println(f);            /**             * 获取方法的信息             */            Method[] methods = clazz.getDeclaredMethods();            Method m01 = clazz.getDeclaredMethod("getUname", null);            // 如果方法有参,则必须传递参数类型对应的class对象            Method m02 = clazz.getDeclaredMethod("setUname", String.class);            for (Method method : methods) {                System.out.println("方法" + method);            }            /**             *获取构造器信息              */            Constructor[] constructors = clazz.getDeclaredConstructors();            Constructor c = clazz.getDeclaredConstructor(int.class,int.class,String.class);            System.out.println("获得构造器"+c);            for (Constructor constructor : constructors) {                System.out.println("构造器"+constructor);            }                                            } catch (ClassNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (NoSuchFieldException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (SecurityException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (NoSuchMethodException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }}

通过反射操作类的属性,方法构造器

import java.lang.reflect.Constructor;import java.lang.reflect.Field;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import bean.User;/** * @author clc * */public class Test3 {    public static void main(String[] args) {        try {            Class
       
         clazz = (Class
        
         ) Class.forName("bean.User");            // 通过反射API调用构造方法,构造对象            // 其实调用了User的无参构造方法            User u1 = clazz.newInstance();            System.out.println(u1);            // 有参调用构造器            Constructor
         
           c = clazz.getDeclaredConstructor(int.class, int.class, String.class);            User u2 = c.newInstance(1234, 22, "clc");            System.out.println(u2);            // 通过反射调用普通方法            User u3 = clazz.newInstance();            Method method = clazz.getDeclaredMethod("setUname", String.class);            // 相当于u3.setUname("clc3");            method.invoke(u3, "clc3");            System.out.println(u3);            // 通过反射操作属性            User u4 = clazz.newInstance();            Field f = clazz.getDeclaredField("uname");            // 设置属性不需要安全检查,可以直接访问            f.setAccessible(true);            // 通过反射直接设置属性            f.set(u4, "clc4");            // 通过反射直接读取属性值            System.out.println(u4.getUname());            System.out.println(f.get(u4));        } catch (ClassNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (InstantiationException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IllegalAccessException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (NoSuchMethodException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (SecurityException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IllegalArgumentException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (InvocationTargetException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (NoSuchFieldException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }}

辅助类User

package bean;public class User {    private int id;    private int age;    private String uname;    @Override    public String toString() {        return "User [id=" + id + ", age=" + age + ", uname=" + uname + "]";    }    @Override    public int hashCode() {        final int prime = 31;        int result = 1;        result = prime * result + age;        result = prime * result + id;        result = prime * result + ((uname == null) ? 0 : uname.hashCode());        return result;    }    @Override    public boolean equals(Object obj) {        if (this == obj)            return true;        if (obj == null)            return false;        if (getClass() != obj.getClass())            return false;        User other = (User) obj;        if (age != other.age)            return false;        if (id != other.id)            return false;        if (uname == null) {            if (other.uname != null)                return false;        } else if (!uname.equals(other.uname))            return false;        return true;    }    public int getId() {        return id;    }    public void setId(int id) {        this.id = id;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getUname() {        return uname;    }    public void setUname(String uname) {        this.uname = uname;    }    public User(int id, int age, String uname) {        super();        this.id = id;        this.age = age;        this.uname = uname;    }    public User() {        super();    }}