（1-9-3） Java 反射 Reflect

qq_43457850

919人浏览 · 2025-08-10 14:11:35

qq_43457850 · 2025-08-10 14:11:35 发布

03. 异常1：ClassNotFoundException

04. 异常2：InstantiationException

05. 异常3：IllegalAccessException

3.5 config.properties

3.6 Application

3.7 实现效果

1. 介绍反射与其作用

1.1 什么是反射

1.2 对比传统方式与反射方式

00. base

package com.imooc.reflect;

/**
 * 四则运算接口
 */
public interface MathOperation {
    public float operate(int a , int b);
}

package com.imooc.reflect;

/**
 * 加法
 */
public class Addition implements MathOperation {
    @Override
    public float operate(int a , int b) {
        System.out.println("执行加法运算");
        return a + b;
    }
}

package com.imooc.reflect;

/**
 * 减法运算
 */
public class Subtraction implements MathOperation {
    @Override
    public float operate(int a, int b) {
        System.out.println("执行减法运算");
        return a - b;
    }
}

01. 传统创建对象方式

public class ReflectSample {
    /**
     * 传统的创建对象方式
     */
    public static void case1(){
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入计算类名:");
        String op = scanner.next();
        System.out.print("请输入a:");
        int a = scanner.nextInt();
        System.out.print("请输入b:");
        int b = scanner.nextInt();
        MathOperation mathOperation = null;
        if(op.equals("Addition")){
            mathOperation = new Addition();
        }else if(op.equals("Subtraction")) {
            mathOperation = new Subtraction();
        }else if(op.equals("Multiplication")){
            mathOperation = new Multiplication();
        }else{
            System.out.println("无效的计算类");
            return;
        }
        float result = mathOperation.operate(a, b);
        System.out.println(result);
    }




    public static void main(String[] args) {
        ReflectSample.case1();
    }
}

02. 通过反射创建对象

package com.imooc.reflect;

import java.util.Scanner;

/**
 * 初识反射的作用
 */
public class ReflectSample {
    /**
     * 利用反射在运行时  动态创建对象
     */
    public static void reflectDemo(){
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入计算类名:");
        String op = scanner.next();
        System.out.print("请输入a:");
        int a = scanner.nextInt();
        System.out.print("请输入b:");
        int b = scanner.nextInt();
        MathOperation mathOperation = null;
        // 找到[包名（路径） + 类名]
        // 在对其进行实例化
        // 最后通过接口类型的变量接收
        try {
            mathOperation = (MathOperation)Class.forName("com.imooc.reflect." + op).newInstance();
        } catch (Exception e) {
            System.out.println("无效的计算");
            e.printStackTrace();
            // 让程序中断
            return;
        }
        float result = mathOperation.operate(a, b);
        System.out.println(result);
    }


    public static void main(String[] args) {
        ReflectSample.reflectDemo();
    }
}

03. 直观对比

2. 反射的四个核心类

2.1 Class 类

（1）. Class 类概述与核心方法

（2） Class.forName()

00. base & 效果

01. Employee

package com.phdvb.reflect.entity;

import java.util.Date;

public class Employee {
    private Integer empno;
    private String ename;
    private String job;
    private Integer mgr;
    private Date hiredate;
    private Float sal;
    private Float comm;
    private Integer deptno;
    public Employee() {
        System.out.println("Employee Constructor 已经执行！");
    }

    public Integer getEmpno() {
        return empno;
    }

    public void setEmpno(Integer empno) {
        this.empno = empno;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public int getMgr() {
        return mgr;
    }

    public void setMgr(Integer mgr) {
        this.mgr = mgr;
    }

    public Date getHiredate() {
        return hiredate;
    }

    public void setHiredate(Date hiredate) {
        this.hiredate = hiredate;
    }

    public float getSal() {
        return sal;
    }

    public void setSal(Float sal) {
        this.sal = sal;
    }

    public float getComm() {
        return comm;
    }

    public void setComm(Float comm) {
        this.comm = comm;
    }

    public int getDeptno() {
        return deptno;
    }

    public void setDeptno(Integer deptno) {
        this.deptno = deptno;
    }
}

02. ClassDemo

package com.phdvb.reflect;

import com.phdvb.reflect.entity.Employee;

public class ClassDemo {
    public static void main(String[] args) {
        // Class.forName() 方法将指定的类加载到 jvm
        // 并返回 class 对象
        try {
            Class empClass = Class.forName("com.phdvb.reflect.entity.Employee");
            System.out.println("Employee类 已经加载到了 jvm !");

            // 得到 employ 这个类的对象
            Employee emp = (Employee)empClass.newInstance();
            System.out.println(emp);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }
}

03. 异常1：ClassNotFoundException

04. 异常2：InstantiationException

05. 异常3：IllegalAccessException

2.2 Constructor 构造方法

（1）两个重要方法

（2）案例实现

00. base & 效果

01. Employee

package com.phdvb.reflect.entity;

import java.util.Date;

// 经过abstract 修饰的类无法实例化
//public abstract class Employee {
public class Employee {
    private Integer empno;
    private String ename;
    private String job;
    private Integer mgr;
    private Date hiredate;
    private Float sal;
    private Float comm;
    private Integer deptno;
    private Employee() {
//    public Employee() {
        System.out.println("Employee Constructor 已经执行！");
    }

    public Employee(Integer empno, String ename, String job, Integer mgr, Date hiredate, Float sal, Float comm, Integer deptno) {
        this.ename = ename;
        this.job = job;
        this.empno = empno;
        this.mgr = mgr;
        this.hiredate = hiredate;
        this.sal = sal;
        this.comm = comm;
        this.deptno = deptno;
        System.out.println("Employee带参构造方法已被执行");
    }

    public Integer getEmpno() {
        return empno;
    }

    public void setEmpno(Integer empno) {
        this.empno = empno;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public int getMgr() {
        return mgr;
    }

    public void setMgr(Integer mgr) {
        this.mgr = mgr;
    }

    public Date getHiredate() {
        return hiredate;
    }

    public void setHiredate(Date hiredate) {
        this.hiredate = hiredate;
    }

    public float getSal() {
        return sal;
    }

    public void setSal(Float sal) {
        this.sal = sal;
    }

    public float getComm() {
        return comm;
    }

    public void setComm(Float comm) {
        this.comm = comm;
    }

    public int getDeptno() {
        return deptno;
    }

    public void setDeptno(Integer deptno) {
        this.deptno = deptno;
    }
}

02.ConstructorDemo

package com.phdvb.reflect;


import com.phdvb.reflect.entity.Employee;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * 利用带参构造方法创建对象
 */
public class ConstructorDemo {
    public static void main(String[] args) {
        try {
            Class employeeClass = Class.forName("com.phdvb.reflect.entity.Employee");
            Constructor constructor = employeeClass.getConstructor(new Class[]{
                    Integer.class, String.class, String.class, Integer.class, Date.class, Float.class, Float.class, Integer.class
            });
            Employee employee = (Employee) constructor.newInstance(new Object[]{
                    11111, "剖好的VB", "教师", 8888,
                    new SimpleDateFormat("yyyy-MM-dd").parse("2025-08-06"),
                    5500f, 3500f, 20
            });
            System.out.println(employee);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            //没有找到与之对应格式的方法
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            //当被调用的方法的内部抛出了异常而没有被捕获时
            e.printStackTrace();
        }catch (ParseException e) {
            throw new RuntimeException(e);
        }
    }
}

2.3 Method 方法类

（1）Method概述与核心方法

（2）案例实现

00. base & 效果

01. Employee

package com.phdvb.reflect.entity;

import java.util.Date;

// 经过abstract 修饰的类无法实例化
//public abstract class Employee {
public class Employee {
    private Integer empno;
    private String ename;
    private String job;
    private Integer mgr;
    private Date hiredate;
    private Float sal;
    private Float comm;
    private Integer deptno;
    private Employee() {
//    public Employee() {
        System.out.println("Employee Constructor 已经执行！");
    }

    public Employee(Integer empno, String ename, String job, Integer mgr, Date hiredate, Float sal, Float comm, Integer deptno) {
        this.ename = ename;
        this.job = job;
        this.empno = empno;
        this.mgr = mgr;
        this.hiredate = hiredate;
        this.sal = sal;
        this.comm = comm;
        this.deptno = deptno;
        System.out.println("Employee带参构造方法已被执行");
    }

    public Integer getEmpno() {
        return empno;
    }

    public void setEmpno(Integer empno) {
        this.empno = empno;
    }

    public String getEname() {
        return ename;
    }

    public void setEname(String ename) {
        this.ename = ename;
    }

    public String getJob() {
        return job;
    }

    public void setJob(String job) {
        this.job = job;
    }

    public int getMgr() {
        return mgr;
    }

    public void setMgr(Integer mgr) {
        this.mgr = mgr;
    }

    public Date getHiredate() {
        return hiredate;
    }

    public void setHiredate(Date hiredate) {
        this.hiredate = hiredate;
    }

    public float getSal() {
        return sal;
    }

    public void setSal(Float sal) {
        this.sal = sal;
    }

    public float getComm() {
        return comm;
    }

    public void setComm(Float comm) {
        this.comm = comm;
    }

    public int getDeptno() {
        return deptno;
    }

    public void setDeptno(Integer deptno) {
        this.deptno = deptno;
    }

    public Employee updateSal(Float sal) {
        float preSal = this.sal;
        this.sal = this.sal + sal;
        System.out.println(this.ename + "的薪资由" + preSal +", 调整到了" + this.sal);
        return this;
    }
}

02. MethodDemo

package com.phdvb.reflect;

import com.phdvb.reflect.entity.Employee;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class MethodDemo {
    public static void main(String[] args) {
        try {
            Class empClass = Class.forName("com.phdvb.reflect.entity.Employee");
            Constructor constructor = empClass.getConstructor(new Class[]{
                    Integer.class, String.class, String.class, Integer.class, Date.class, Float.class, Float.class, Integer.class
            });
            Employee employee = (Employee) constructor.newInstance(new Object[]{
                    11111, "剖好的VB", "教师", 8888,
                    new SimpleDateFormat("yyyy-MM-dd").parse("2025-08-06"),
                    5500f, 3500f, 20
            });
            System.out.println("pre-Emp: " + employee);
            System.out.println("pre-Emp: emp-Sal" + employee.getSal());

            Method updateSalMethod = empClass.getMethod("updateSal", new Class[]{Float.class});
            Employee employee1 = (Employee) updateSalMethod.invoke(employee, new Object[]{1500f});
            System.out.println("post-Emp:" + employee1);
            System.out.println("post-Emp: emp-Sal" + employee1.getSal());
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        } catch (ParseException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }

    }
}

2.4 Field 成员变量类

（1） Field 概述与核心方法

（2）案例实现

00.base & 效果

01. FieldDemo

package com.phdvb.reflect;

import com.phdvb.reflect.entity.Employee;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 * 通过 Field 对成员变量  赋值与取值
 */
public class FieldDemo {
    public static void main(String[] args) {
        try {
            Class empClass = Class.forName("com.phdvb.reflect.entity.Employee");
            Constructor constructor = empClass.getConstructor(new Class[]{
                    Integer.class, String.class, String.class, Integer.class, Date.class, Float.class, Float.class, Integer.class
            });
            Employee employee = (Employee) constructor.newInstance(new Object[]{
                    11111, "剖好的VB", "教师", 8888,
                    new SimpleDateFormat("yyyy-MM-dd").parse("2025-08-06"),
                    5500f, 3500f, 20
            });

            Field enameField = empClass.getField("ename");
            String ename = (String) enameField.get(employee);
            System.out.println("获取员工原先的名称：" + ename);
            enameField.set(employee, "phdvb");
            String ename1 = (String) enameField.get(employee);
            System.out.println("获取完善后员工的名称：" + ename1);
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        } catch (ParseException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (NoSuchFieldException e) {
            throw new RuntimeException(e);
        }
    }
}

2.5 getDeclared方法

（1）getDeclared 概述

（2）具体案例

00. base & 效果

01. Employee

02. getDeclaredDemo

package com.phdvb.reflect;

import com.phdvb.reflect.entity.Employee;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class getDeclaredDemo {
    public static void main(String[] args) {
        try {
            Class empClass = Class.forName("com.phdvb.reflect.entity.Employee");
            Constructor constructor = empClass.getConstructor(new Class[]{
                    Integer.class, String.class, String.class, Integer.class, Date.class, Float.class, Float.class, Integer.class
            });
            Employee employee = (Employee) constructor.newInstance(new Object[]{
                    11111, "剖好的VB", "教师", 8888,
                    new SimpleDateFormat("yyyy-MM-dd").parse("2025-08-06"),
                    5500f, 3500f, 20
            });
            Field[] fields = empClass.getDeclaredFields();
            for (Field field : fields) {
                System.out.print(field.getName() + " | ");
                //empno | ename | job | mgr | hiredate | sal | comm | deptno |
                if (field.getModifiers() == 1) {  // 属性被 public 所修饰
                    Object value = field.get(employee);
                    System.out.println(field.getName() + ":" + value);
                }else if(field.getModifiers() == 2) {  // 属性被 private 修饰
                    String methodName = "get" + field.getName().substring(0, 1).toUpperCase() + field.getName().substring(1);
                    System.out.println("methodName:" + methodName);
                    Method method = empClass.getMethod(methodName);
                    Object ret = method.invoke(employee);
                    System.out.println(field.getName() + ":" + ret);
                }
            }
        } catch (ClassNotFoundException e) {
            throw new RuntimeException(e);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        } catch (ParseException e) {
            throw new RuntimeException(e);
        }

    }
}

3. 反射在I18N项目中的应用

3.1 目录

3.2 I18N

package com.i18n.reflect;

public interface I18N {
    public String say();
}

3.3 En

package com.i18n.reflect;

public class En implements I18N{
    @Override
    public String say() {
        return "Life is endless, and the struggle is endless.";
    }
}

3.4 Zhcn

package com.i18n.reflect;

public class Zhcn implements I18N{
    @Override
    public String say() {
        return "生命不息，奋斗不止";
    }
}

3.5 config.properties

#language=com.i18n.reflect.Zhcn
language=com.i18n.reflect.En

3.6 Application

package com.i18n.reflect;

import java.io.FileInputStream;
import java.net.URLDecoder;
import java.util.Properties;

public class Application {
    public static void say(){
        Properties properties = new Properties();
        String configPath = Application.class.getResource("/config.properties").getPath();
        System.out.println("configPath1: " + configPath);
        //configPath1: /D:/s_java/se/9-3reflect/math/out/production/math/config.properties

        try {
            configPath = new URLDecoder().decode(configPath, "UTF-8");
            System.out.println("configPath2: " + configPath);
            //configPath2: /D:/s_java/se/9-3reflect/math/out/production/math/config.properties
            properties.load(new FileInputStream(configPath));
            String language = properties.getProperty("language");
            System.out.println("language: " + language);
            //language: com.i18n.reflect.Zhcn
            I18N i18N = (I18N) Class.forName(language).newInstance();
            System.out.println("i18N: " + i18N);
            //i18N: com.i18n.reflect.Zhcn@4554617c
            System.out.println(i18N.say());
            //生命不息，奋斗不止
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    public static void main(String[] args) {
        Application.say();
    }
}

3.7 实现效果

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已为社区贡献3条内容

（1-9-3） Java 反射 Reflect

qq_43457850

1. 介绍反射与其作用

1.1 什么是反射

1.2 对比传统方式与反射方式

00. base

01. 传统创建对象方式

02. 通过反射创建对象

03. 直观对比

2. 反射的四个核心类

2.1 Class 类

（1）. Class 类概述 与 核心方法

（2） Class.forName()

00. base & 效果

01. Employee

02. ClassDemo

03. 异常1：ClassNotFoundException

04. 异常2：InstantiationException

05. 异常3：IllegalAccessException

2.2 Constructor 构造方法

（1）两个重要方法

（2）案例实现

00. base & 效果

01. Employee

02.ConstructorDemo

2.3 Method 方法类

（1）Method概述 与 核心方法

（2）案例实现

00. base & 效果

01. Employee

02. MethodDemo

2.4 Field 成员变量类

（1） Field 概述 与 核心方法

（2） 案例实现

00.base & 效果

01. FieldDemo

2.5 getDeclared方法

（1）getDeclared 概述

（2） 具体案例

00. base & 效果

01. Employee

02. getDeclaredDemo

3. 反射在I18N项目中的应用

3.1 目录

3.2 I18N

3.3 En

3.4 Zhcn

3.5 config.properties

3.6 Application

3.7 实现效果

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（1）. Class 类概述与核心方法

（1）Method概述与核心方法

（1） Field 概述与核心方法

（2）案例实现

（2）具体案例